Influence of management type on Diptera communities of coniferous plantations and deciduous woodlands

The contribution of four types of secondary woodlands to Scottish invertebrate biodiversity was investigated for coniferous plantation forestry, riparian ash-alder woodlands, early successional deciduous woodlands and climax deciduous woodlands. Considerable variation in the type and intensity of management within these four woodland types existed. Adult Diptera from 21 families, representing diverse trophic and ecological guilds, were sampled from 31 woodlands in the Aberdeenshire region of northeast Scotland, between June and August 2001. Environmental differences between woodlands were recorded at each site using environmental parameters such as pH and organic matter content, vegetation characteristics, including percentage canopy cover and dominant field layer plant species. Multivariate ordination techniques detected significant responses in the Dipteran communities to soil type, organic matter content, soil pH, field layer plant species richness, dominant field layer plant species and percentage cover of Pteridium aquilinum. Responses in terms of Dipteran abundance, species richness, diversity and evenness were observed to soil type and dominant species of the field layer vegetation. The role of woodland type and management in diversifying Diptera communities is discussed with a view to maintain and possibly enhance Dipteran and other invertebrate communities in Scottish secondary woodlands. (C) 2002 Elsevier Science B.V. All rights reserved.

川西亚高山人工针叶林下11种植物对两种光生境的适应性研究

青藏高原东缘的亚高山针叶林是长江上游重要的生态屏障，经过近六十年的采伐后，取而代之的是大量人工种植的云杉纯林。目前，这些人工林已经表现出树种单一，结构层次简单等生态问题，其物种多样性及生态效益与同地带天然林相比差距较明显。如何丰富该地区物种多样性，完善人工林生态系统的生态功能是一个十分重要的课题。林下植物是人工林群落的重要组成部分，对维持群落的生物多样性及完善生态系统功能具有明显的作用。因此，研究该地区人工针叶林的林下植被对不同生境的适应性对于理解人工林生态系统物种多样性的形成和维持机制都具有重要的意义。 本文以青藏高原东部亚高山针叶林的主要森林类型----云杉人工林为研究对象，选择林下11种具有不同喜光特性的常见植物，分别设置人工林林冠下及成熟林窗为研究样地，通过对各种植物叶片形态与物质分配特征、叶片解剖学特征、叶片光合生理特性、植物自然分布特征等方面的比较分析，研究林下植物对不同光生境的适应策略及其适应能力，揭示不同物种对人工林生境的适应共性，为西南亚高山地区植被恢复及人工林的经营管理提供科学依据。具体研究结果如下： 在叶片形态和物质分配特征方面：在林窗光生境中，11种林下植物叶片比叶重(LMA)显著高于林下光生境的同种植物。同时，林窗下生长的植物叶片叶片厚度及栅栏细胞长度显著增加，这是影响叶片比叶重变化的直接原因。而多数植物叶重比在两种生境中无明显变化。说明在长期适应自然生境之后，植物可能更多地采取调节叶片组织细胞水平（即叶片功能细胞形态）及叶片器官水平（即单个叶片形态）特征的策略来适应各类生境，而非整株水平上的叶片总比重的增减。 在叶片解剖结构特征方面：多数阔叶物种栅栏组织厚度(PT)、栅栏组织厚度/海绵组织厚度(PT/ST)、栅栏细胞层数及近半数种的气孔密度(SD)在林窗生境中更大或更多，而叶片表皮细胞厚度(UET、LET)气孔长径(SL)及海绵组织厚度(ST)受两种生境影响不大。喜光特性相似的物种在生境适应策略上具有一定的趋同性。 在光合生理特征方面：在林窗生境中多数种植物的最大光合速率(Amax)、暗呼吸速率(Rd)及喜光植物光补偿点(LCP)显著或极显著高于林内生境同种植物。且在同一生境条件下，多数深度耐荫植物比喜光及轻度喜光植物有稍低的Rd和LCP。各植物在林内低光生境中具有更大的内禀光能转化效率，并在中午12:00～14:00之间光强最大的时刻发生了的最深程度的光抑制。多数种能通过调节自身某种光合素含量或色素之间的比例来适应不同的光生境，即通过增加叶绿素含量或降低Chla/b值来适应林内弱光生境，通过提高类胡萝卜素含量或单位叶绿素的类胡萝卜素含量降低强光带来的伤害。绝大多数物种并不采取调节叶片C、N含量的策略来适应不同的光生境。总之，植物部分光合参数(Amax、Rd、LCP)受生境的影响与其自身喜光特性有关，但另一些参数（Fv/Fm日变化、色素含量及比例、叶氮相对含量）受生境影响与其自身喜光特性无明显关联。 在表型可塑性方面：在叶片各表型参数中，器官水平及细胞水平的形态特征参数平均可塑性大于整株水平形态和物质分配特征参数可塑性；叶片光合组织的可塑性大于非光合组织可塑性；反映植物光合能力的参数可塑性大于叶片色素含量参数可塑性。植物叶片形态和物质分配、解剖学特征参数平均可塑性大小与其自身喜光特性基本吻合，即喜光种及轻度耐荫种各参数可塑性最高，深度耐荫种可塑性最小，而这种规律并未在光合生理参数的可塑性大小上体现出来。但是叶片形态和物质分配参数、光合生理参数的平均可塑性水平却大于叶片解剖学参数。 在植物自然分布特征方面：喜光物种云杉幼苗及歪头菜在林内生境中分布密度明显降低，深度耐荫种疏花槭却恰恰相反，更多数物种（7种植物）在两种生境中密度变化趋势不明显。从分布格局来看，7种植物在两种生境中均为聚集分布，但聚集强度为林窗>林内；少数物种桦叶荚迷、直穗小檗、冰川茶藨、黄背勾儿茶在林窗中为聚集型，在林内生境中的分布型发生改变而成为随机型，说明光生境的差异能影响到植物种群的分布特征。但这种影响程度与植物自身的喜光特性无关，同时与各物种叶片表型平均可塑性的大小也无明显关联。 The subalpine coniferous forest area in eastern Qinghai-Tibet Plateau is important ecology-barrier of upriver Yangtze. In past sixty years, those forests had been cut down and replaced with a lot of spruce plantations. At now, there are many ecology problems presenting to us such as singleness species, simple configuration, lower species diversity and ecological benefit than natural forests at the same belt. How to restore the species diversity and enhance the eco-function of the plantations is a very important issue. The understory plants are important part of plantation community, which improved the bio-diversity and eco-function distinctly of forests. So, it is very significance to study the adaptation of understory plants to different environment in plantation, and this study would helping us to understand how plantations to develop and remain their biodiversity. This study was conducted in a 60a spruce plantation in Miyaluo located in western Sichuan, China, and spruce plantation is major types of subalpine coniferous forest in eastern Qinghai-Tibet Plateau. In this paper, the leaf morphological and biomass-distributed characteristics, the anatomical characteristics, the photosynthetic characteristics and the distribution patterns characteristics of eleven different light-requirement understory species grown in two different environments (forest gaps and underneath close canopy) were studied and compared. The purpose of this study was to analyze the adaptation of this forest understory plants, to show up the commonness of these different light-requirement understory species in light acclimation, and to provide some scientific reference to manage and restore the vegetation of subalpine plantation of southwest China. The results were as follows: The leaf morphological and biomass-distributed characteristics: These eleven species in forest gaps had significantly higher dry weight per leaf area (LMA) than those under close canopy. The palisade parenchyma cells of the broad-leaved species in gaps were significantly longer than those grown under the canopy, which been a directed factor for the change of leaf mass per unit area (LMA) in different environment. But the leaf weight ratio (LWR) of most plants species were not evidently changed by the contrasted environments in our study. It was shown the morphological characteristics changing been adopted as a strategy of light acclimation for plants wasn’t on whole plant level (leaf weight ratio) but cellular level (the function cells morphological characteristics) and organic level (the leaf morphological and biomass-distributed characteristics) mostly. The leaf anatomical characteristics: Most broad-leaved plants in gaps increased palisade parenchyma thickness (PT), the palisade parenchyma cell layers and the ratio of palisade to spongy parenchyma (PT/ST). So did as almost about half species in this study in stomatal density (SD). No significant differences in thickness of leaf epidermal cells (UET, LET), stomatal length (SL) and spongy parenchyma (ST) between two environments of most species were observed. The results suggested that species with light-requirement approximately had convergent evolution on adaptation to light condition. The leaf photosynthetic characteristics: The dark respiration rate (Rd) of most plants species, the light compensation point (LCP) of light-demanding plants species in gaps were significantly increased than under close canopy in this study. In a same habitat, most deep-shade-tolerant plants had lower Rd and LCP than those light-demanding plants and slight-shade-tolerant plants. Each species has bigger inherent electron transport rate under close canopy than in gaps, and the greatest photoinhibition happened during 12 to 14 in the daytime. Most species could adapt different light environment by the way of changing their photosynthetic pigments content or the ratio of pigments content. For example, some plants under close canopy increased chlorophyll (Chl) or reduced the values of the ratio Chla/b to adapted the low light condition, some plants in gaps increased carotenoid (Car) or reduced the weight ratio CarChl to avoid been hurt in high light. For most plants, changing the content of C and N in leaf wasn’t a strategy of light acclimation. In conclusion, the variation of some leaf photosynthetic parameters in different light environment such as Fv/Fm, pigments, C and N in leaf related with the light-requirmnet of species, but the others such as Amax, Rd, LCP did not. The leaf plasticity indexes: Among those leaf plasticity indexes, the leaf morphological and biomass-distributed parameters on cellular and organic level were greater than on whole plant level for same species, and the photosynthetic parenchyma parameters were greater than non-photosynthetic parenchyma parameters in same leaf, and photosynthetic capability parameters were greater than photosynthetic pigments content parameters for same species. The average plasticity indexes of leaf morphological and biomass-distributed and anatomical parameters were accordant with plants’ light-requirement approximately: those light-demanding plants and slight-shade-tolerant plants had bigger plasticity indexes than deep-shade-tolerant plants. But this regular wasn’t observed in physiological plasticity indexes for most plants, though the average leaf plasticity indexes of leaf morphological and biomass-distributed, photosynthetic characteristics parameters was greater than the anatomical characteristics parameters. The distribution patterns characteristics: Oppositely to the deep-shade-tolerant specie Acer laxiflorum Pax., the density of light-demanding species Picea asperata Mast. and Vicia unijuga A. Br. in gaps was bigger than under close canopy. Each of the other species has the approximately density in two different environment. The spatial patterns of seven species were aggregated distribution in two environments, but the trend of aggregation of population under close canopy was decrease from in gaps. A few species such as Viburnum betulifoium Batal., Berberis dasystachya Maxim., Ribes glaciale Wall. and Berchemia flavescens Brongn. were aggregated distribution in gaps while random distribution under close canopy. It was shown that the difference between two light environments could affect the distribution pattern of plant population, and the effect didn’t relate with the light-requirement or plasticity indexes of species.

川西亚高山云杉人工林天然更新与生境异质性研究

川西亚高山针叶林是四川森林的主体，是长江上游重要的生态屏障。云杉作为亚高山针叶林人工更新的主要树种，已经在该地区形成了大面积的人工纯林。目前，许多云杉人工林分已经进入更新成熟龄，而这些人工林的持续更新却成为日益凸现的问题。探讨这些云杉人工林的自我更新潜力及云杉种子种群更新特点，可为培育后续森林资源提供科学依据。 本文以川西米亚罗亚高山60a云杉人工林为研究对象，并以该区域内相对稳定的植被群落——天然林为对照，采用种子收集器、土壤种子库筛选、室内外种子萌发实验及野外幼苗调查等方法，从异质性微生境的角度研究了种子雨下落之后，不同微生境对种子库、种子萌发、幼苗建立及分布这一前期更新过程的影响，得出如下结果： 1、通过对川西亚高山60a云杉人工林和天然林6年内种子雨雨量、形态特征、散步动态等的持续观测和综合比较可以发现，云杉林结实特点由于林木自身的特征存在着巨大的变动，2002年和2006年两个种子结实大年内，60a人工林种子雨强度分别达到1088.2 ± 52.3粒/m2和704.3 ± 48.9粒/m2，远大于天然林579.9 ± 28.9粒/m2 和507.5± 30.7粒/m2；且云杉林结实质量优于天然林。60a人工林结实量大，种子质量也最好，相对天然林来说对种群的天然更新以及群落的演替都有最大的贡献潜力。应该说，在川西亚高山云杉人工林的天然更新过程中，种源不是影响天然更新的因素。在种子结实大年里，达到更新成熟的云杉人工林有着优于该地区相对稳定植被群落——天然林的种源优势。至少在种子结实大年，种子供应不是该区域人工林天然更新的限制因子。 2、相对于天然林种子库，人工林种子库在种子萌发前能够有较多的有活力种子。虽然这其中有种子雨输入量有差别的因素存在，但两种林分种子库对种子的保存率的不同才是造成这种差异的主要因素。在人工林中，不同地被类型形成的微生境显著地影响了种子库中种子的密度、垂直分布。有地被物存在的微生境能够将种子雨的大部分截留在地被层中，成为幼苗出现的主要场所；同时不同的地被物对种子的保存情况存在显著的差异，苔藓和凋落物层能都较好地保持其中的种子，到种子萌发前，这两种种子库类型能分别为天然更新提供366.1粒/m2和302粒/m2的有效种子。从这点来看，林下地被物上的种子库能够为天然更新萌发阶段提供数量可观的物质基础。 3、种子的萌发和幼苗的定居是天然更新过程中种子库向幼苗库转化的关键环节。总的说来，米亚罗人工林区60a云杉人工林种子向幼苗的转化率十分低下，凋落物、苔藓、草本、裸地四种主要地被物以及天然林内种子/幼苗的转化率分别仅为2.22%、2.14%、0.57%、0.67%、1.05%。这种低的转化率成为云杉林天然更新的限制性因子。但在现有更新条件下，微生境对这一环节仍然显示出十分显著的影响，表现为凋落物和苔藓对现有更新的新幼苗的保存率高于其它类型及天然林。苔藓和凋落物在种子萌发，幼苗保存，以及幼苗分布上都要优于其它地被物类型；另外，微地形对天然更新过程的影响也很显著，凹立地上更适宜于种子的汇集、萌发和定居。 Subalpine coniferous forests dominate most parts of the forested areas in western Sichuan, and they are important ecological barriers in the upper reaches of the Yangtze River. Picea asperata is one of the keystone spruce species for re-afforestation after felling of the natural forests and there have been a total of ca. 13 000 ha of plantations dominate by this species established. Nowadays, many P. asperata plantations have reached reproductive maturity. However, continued regeneration becomes to an important problem in these plantations. Understanding their self-regeneration potential and the regeneration characteristics of seed populations in spruce plantations of these plantations can have some insights on the management of these plantations and the establishment of following forest resources. A subalpine 60a P. asperata plantation distributed in Miyaluo artificial forest area was studied in this paper, at the same time. Synchronously, a 150a natural spruce forest was studied as comparison. Using seed collecting traps, sieving method for soil seed bank, seed germination experiments and seedling investigations in the field, the effects of heterogeneous microsites on early natural regeneration processes after seed rain were studied, which included seed banks, seed germination, seedling establishment and distribution. The main results are as follows. 1. Through a 6-year long term investigation of seed rain intensities, characteristic, dispersal dynamics of 60a P. asperata plantation, we could concluded that the seed setting properties of 60a P. asperata plantation have a great variation for the characteristics trees. In the mast seed year of 2002 and 2006, the seed rain intensities of plantation was 1088.2 ± 52.3 seeds/m2 and 704.3 ± 48.9 seeds/m2 respectively, which were much greater than that of natural spruce forest (579.9 ± 28.9 seeds/m2 in 2002, and 507.5± 30.7 seeds/m2 in 2006). Furthermore, the quality of seed rain in P. asperata plantation was better than that of natural spruce forest. Contrasting with natural spruce forest, 60a P. asperata plantation has a greater potential on natural regeneration of P. asperata population and succession of community for the reason of greater seed rain intensities and better seed quality. We can confirm that seed source was not a limiting factor which influences the natural regeneration progress of P. asperata population distributed in subalpine mountain zone, at least in the mast seed year. 2. Contrasting with natural spruce forest, P. asperata population had more viable seeds in seed bank before the germination. Although the difference of seed rain intensities of two forests has effect on this phenomenon, the difference of seed conservation ability in two forests was the main factor. In the P. asperata plantation, the seed densities and seed vertical distribution pattern were significant effected by the microsites, which posed by different ground cover types. In other word, Microsite with ground covers can obstruct most seeds and keep them in ground cover layer from seed rain, and these ground covers would be the main site for seed occurrence. There was a significant difference about seeds conservation ability among these ground covers. Litter and moss could better conserve P. asperata seeds which distributed in this two covers. Seed banks exist in litter and moss ground cover types could respectively provide 302seed/m2 and 366.1seed/m2 for natural regeneration before the seed germination. From this point of view, we could conclude that ground covers can ensure considerable numbers of seeds for the germination process. 3. Seed germination and seed establishment are key steps that the seeds invert to seedlings in natural generation process. In sum, the seed/seeding transform rate in 60a P. asperata plantation distributed in Miyaluo artificial forest area is very low. the seed/seeding transform rates in litter, moss, herb, soil surface and natural spruce forest were 2.22%、2.14%、0.57%、0.67%、1.05%, respectively. The low transform rate become to a limiting factor of P. asperata natural regeneration process. However, under the existing conditions of natural regeneration, microsit still had significant effect on this transform. The states of Seed germination, new seedling conservation, and older seedling distribution in litter and moss were better than in any other ground cover type or natural spruce forest. In addition, the micro-relief has significant effect on natural regeneration process. Concave site was more suitable for seed collection, seed germination and seedling distribution.

岷江冷杉林群落几种树苗对光强的响应与适应

在青藏高原东部的亚高山针叶林区，如何尽快恢复这一生态脆弱地区的植被，改变生态环境恶化的趋势，是一个十分重要的课题。光一直被认为是植物种间相互替代，尤其是森林演替过程中植物相互替代或植被恢复中的关键环境要素之一。植物能否适应林冠下或林窗中异质的、或多变的光照条件，对其在林中的生存、分布、更新以及森林动态都是非常重要的。 本文以青藏高原东部亚高山针叶林的主要森林类型——岷江冷杉林群落的几种树苗为研究对象，采用实验生态学、生理及生物化学等方法，通过模拟针叶林不同大小林窗内光照强度的变化，在中国科学院茂县生态站内采用遮荫处理设置6个光照梯度（100、55、40、25、15与7%全光照），来研究具有不同喜光特性的植物对光强的响应与适应机制，其研究结果可为揭示亚高山针叶林的演替规律、以及人工林下幼苗的存活与定居提供科学依据，也能为苗木的生产与管理提供科学指导，尤其是对针阔树种在不同光强下的响应与适应的比较研究，能为如何将阔叶树种整合到人工针叶林中提供新的思路。 光强对植物生长的影响 光强对植物的生长具有重要作用，不同植物在各自适宜的光强梯度下才能生长良好。通过一个野外盆栽实验，来研究不同光强对植物生长的影响（第三章）。主要研究结果如下，低光强下植物株高/茎生物量增加，说明植物会将生物量更多用于高生长，以便有效地拦截光资源；在强光下，植物将生物量更多地向根部分配，使得植物在强光下能够吸收更多的水分，而避免干旱胁迫。 在第一个生长季节，以相对生长速率（RGR）表示，红桦和青榨槭在100%全光照下RGR最大，粗枝云杉在55%最大，岷江冷杉在25-40%下较好；然而，在第二个生长季节，2种阔叶树的相对生长速率（RGR）的适宜光强则变为25-55%，云杉为55-100%，而冷杉为25-100%。可见，从第一年到第二年，2种阔叶树苗更适宜在部分荫蔽的条件下生长；而2种针叶树苗对光的需求则逐渐增加，这可能是增加对根生物量相对投资的结果，因为以这种方式，强光下生长的针叶树幼苗更能保持其内部水分平衡，其生长不会因干旱胁迫而受到严重影响。另外，严重遮荫会引起冷杉幼苗死亡。 植物对光强的生理适应 植物可以通过自身形态和生理特征的调整，来发展不同的光能利用策略从而能够在林中共存。通过一个野外盆栽实验，研究了不同光强下生长的几种树苗的生理特征（第四章）对不同光强的响应与适应。结果显示：强光下，粗枝云杉和红桦的光合能力增加，而岷江冷杉和青榨槭在中度遮荫（25-55%）的条件下光合能力最大。植物叶氮和叶绿素含量增高，而光补偿点和暗呼吸速率降低，这些都是植物对低光环境的适应性反应；而强光下植物叶片和栅栏组织变厚，是对强光的一种保护性反应。 植物对光的可塑性反应 不同植物会表现出对光适应有利的生理和形态可塑性反应。本文对第三章、第四章的实验数据进行可塑性指数分析，来研究植物对光强的表型可塑性反应（第五章）。结果显示，生理特征调整是植物对不同光环境的主要适应途径。红桦和青榨槭的可塑性指数平均值要大于粗枝云杉和岷江冷杉，充分表明这2种阔叶树在生理和形态上较强的可塑性更有利于对光环境的适应，而具有比耐荫树种更强的适应能力。另外，2种针叶树相比，云杉的适应性更强。本研究结果支持树种的生理生态特性决定了其演替状况和生境选择的假说。 植物的光抑制与防御 当植物叶片吸收了过多光能，会发生光抑制现象。植物对光抑制的敏感性及防御能力对其生长具有重要意义。本文通过两个野外盆栽实验，研究了生长在强光下（第六章）和变化光强下（第八章）植物的光抑制现象及其防御策略。结果表明，在强光下或从遮荫状态转入强光下，植物都会发生光抑制，其对光抑制的敏感性与植物的耐荫性（或喜光）和演替状态有密切联系。长期生长在强光下的植物受到光抑制是可恢复的，而当处于荫蔽环境的植物突然暴露于强光下时，受到的光抑制不能完全恢复，可能是（部分）光合机构受到破坏的缘故。粗枝云杉和青榨槭防御光抑制伤害的能力较强，热耗散是其防御光抑制的主要途径。长期的强光作用能使岷江冷杉和红桦发生严重光抑制，甚至光伤害，而红桦能够通过“凋落老叶，萌发新叶”的途径来适应新的强光环境。 How to restore the vegetation of subalpine coniferous forest in eastern Qinghai-Tibet Plateau, and change the trend of ecological deterioration is a very important issue. Acclimation of tree seedlings to different and varing light environment affects to a great extent the successful regeneration and establishment of subalpine coniferous forests in southwestern China’s montane forest areas, because the ability to respond to such changing resource are commonly assumed to be critical to plant success, and have a growth advantage than others. In this paper, several species seedlings in Abies faxoniana community were chosed to study the response and adaptation to light intensity and the interspecific differences of adaptability in six shaded sheds (100, 55, 40, 25, 15 and 7% of full sunlight) in the Maoxian Ecological Station of Chinese Academy of Sciences. Our results could provide a strong theoretical evidence for understanding the forest succession laws of subalpine coniferous forests, and the survival and settlement of seedlings under plantations, and provide scientific direction for the production and management of seedlings, especially the comparative studies of the acclimation to light between the conifer and broadleaf trees could provide new ideas for how to integrate the broad-leaved trees into the artificial coniferous forest. Growth under different light intensity Light intensity plays an important role on plant growth. One field experiments was conducted to study the growth of tree seedlings of Picea asperata, Abies faxoniana, Betula albo-sinensis and Acer davidii under different light intensities. The results showed that plants under low light environment could increase the specific stem length (stem length/ stem dry mass), in order to effectively intercept light resources, while biomass greater allocation to the roots, could make plants under high light environment absorb more water, and avoid drought stress. During the first growing season, the relative growth rates (RGRs) of Betula albo-sinensis and Acer davidii had the greatest values under the 100% of full light, for 55% of Picea asperata, and for 25-40% of Abies faxoniana. However, in the second growing season the the relative growth rates of the two broad-leaved trees changed and were appropriate for 25-55% of full light, for 55-100% of spruce, and for 25-100% of fir. Thus, from the first year to the second year, two broad-leaved seedlings maybe more suitable to partly shading environment, and two coniferous seedlings would have an increase in light demand, which may be an increased root biomass investment. Because in this way, seedlings grown under high light could better maintain their internal water balance, and thus its growth would not be seriously affected by drought stress. In addition, serious shading would cause fir seedlings to die. Acclimation of physiology to light Plants could coexist in forest ecosystem by forming different strategies of light use. One field experiments was conducted to study the acclimation of tree seedlings to different light intensity of Picea asperata, Abies faxoniana, Betula albo-sinensis and Acer davidii. The results showed that the photosynthetic capacity of Picea asperata and Betula albo-sinensis exhibited a general tendency of increase with more light availability; but for Abies faxoniana and Acer davidii seedlings, their highest values of the same parameters were found under intermediate light regime (i.e. 25-55% of PFD relative to full sunlight). Plants under low light environment could increase the specific stem length (stem length/ stem dry mass), in order to effectively intercept light resources. Leaf nitrogen and chlorophyll content increased, while dark respiration rate and light compensation points decreased, all of which were adaptive response to the low light environment. On the contrary, plants under high light environment had the thicken leaves and palisade tissue, which was a protective response to high light. Phenotypic plasticity to light Phenotypic plasticity can be exhibited in morphological and physiological processes. Physiological characteristical adjustment is the main for plant adaptation to different light environment.The means of plasticity indexes for Betula albo-sinensis and Acer davidii seelings were greater than Picea asperata and Abies faxoniana, amplied that the two broad-leaved trees were much more adaptable to the environment. In addition, spruce had the higher adaptablity than fir. The findings supported the hypothesis that the ecological characteristics of the species determined the biological status and its biological habitat selection. Photoinhibition and photoprotection to light Compared with conifer, broad-leaved trees could better change leaf morphology and adjust biomass allocation to adapt to changing light environment. However, excess light can photoinhibit photosynthesis and may lead to photooxidative destruction of the photosynthetic appatus. Two field experiments were conducted to study the photoinhibition of photosynthesis. The results showed that when plants grown under high light environment or plants transferred from low to high irradiance, the four tree seedlings would undergo a period of photoinhibition. In four species, photoinhibited leaves could recover to initial photosynthetic rates when they were long-term planted under high light environment. However, when plants were suddenly exposed to high irradiance, this photoinhibition could not be reversible, may be the photosynthesis apparatus were (or partly) photooxidatively destructed.

川西亚高山针叶林主要针叶树种年轮生态学研究

米亚罗地区是四川西部较为典型的亚高山针叶林区域之一。为建立该地区主要针叶树种岷江冷杉、云杉、紫果云杉和红杉的年轮宽度年表资料，了解不同海拔高度岷江冷杉原始林和不同恢复过程的人工针叶林及次生混交林树木径向生长规律，结合样地调查，用生长锥钻取了树木芯样做年轮生态学分析。芯样经过标准化程序固定和打磨抛光后，用WinDENDRO图像分析系统测量年轮宽度序列，用COFECHA程序交叉定年和控制测量数据质量，用ARSTAN程序建立了4个主要针叶树种的地区年表和不同海拔高度岷江冷杉林及人工针叶林和次生混交林针叶树的样地年表。 4个主要针叶树种年轮宽度年表的平均敏感度低于0.2，而其晚材宽度年表都具相对较高的平均敏感度。早材宽度与年轮总宽度标准化年表间的相关系数均在0.9以上；晚材宽度与年轮总宽度标准化年表间的相关系数则种间差异较大，红杉的最高，岷江冷杉的最低。岷江冷杉晚材宽度与年轮总宽度的相关性从1970年以后明显下降，而其他种的相关系数则随时间变化较小。树种之间标准化年表显著正相关，而云杉与紫果云杉和红杉与岷江冷杉之间相关系数明显较高。年表序列的第1主分量表达了4个树种树木共同径向生长变化格局；第2至第4主分量分别表达了云杉属和冷杉属、常绿针叶树种和落叶针叶树种以及云杉和紫果云杉树木径向生长变化差异。 不同海拔高度的8个岷江冷杉样地年轮宽度年表序列敏感度大体上随海拔高度升高而降低。各样地早材宽度与年轮总宽度年表之间的相关系数均在0.9以上，且随海拔高度变化不大；晚材宽度与年轮总宽度之间的相关系数随海拔高度的变化较大，并有随海拔升高而降低的趋势。样地年表序列之间相关系数差异很大，高海拔样地年表间多为显著正相关；低海拔样地年表间的相关系数变化不一；高海拔和低海拔样地年表之间相关性较差，且多不显著。样地年表的第1主分量能解释年表序列总方差的37.5%，反映了不同海拔高度岷江冷杉林木共同的径向生长变化格局；第2和第3主分量分别解释总方差的24.5%和18.2%，表现出明显的高海拔和低海拔样地树木间不同的径向生长变化，除一些样地例外，它们一般与低海拔样地年表有正相关，与高海拔样地年表有负相关。在那些另外的样地，海拔以外的其他因素可能也影响了树木径向生长变化。不同海拔高度样地林木的生长抑制和生长释放频率在不同时期表现出较大的差异，表明了不同的干扰历史和林木补充时间。 人工针叶林和次生混交林各样地林木早材宽度与其年轮总宽度年表之间相关系数均高达0.9以上；晚材宽度与年轮总宽度年表之间也都显著正相关，但人工针叶林样地的明显较高。样地年表序列之间的相关关系表现为，林分起源和经营管理相似的样地年表之间的相关系数明显较高，如人工针叶林与人工针叶林尽管树种不同，但样地年表之间显著正相关，而与次生混交林样地年表间关系不显著；反之亦然。综合比较各项生长参数及不同时期的树木径向生长速率，人工针叶林树木的胸径增长至少在40年以内是优于次生混交林的同种（或不同种）针叶树的。不同样地林木生长释放和生长抑制及人工针叶林树木胸高断面积增长分析表明，除严重的人为干扰外，林分郁闭后林木密度过大是造成高频率生长抑制的主要原因，在林分发育的适当时期通过抚育间伐等措施调控林分密度，是保证林木胸高断面积在一定时期内保持较高的连年增长的关键。日本落叶松作为引进的树种，在海拔3100 m左右种植表现良好，近30年来各项生长指标均高于林龄相近的云杉人工林，因此，适当用其作为川西亚高山针叶林采伐迹地快速恢复是合理的。 Miyaluo area is one of the typical regions covered by subalpine coniferous forests in western Sichuan province of southwestern China. To develop the regional tree-ring width chronology series for the dominant conifers such as Abies faxoniana, Picea asperata, P. purpurea and Larix potaninii, and to understand the radial growth patterns of conifers in Abies faxoniana natural forest stands at different altitudes, and in coniferous plantations and natural regenerated mixed stands in their different restoring processes as well, increment cores were sampled in the field together with conventional plots investigations for dendroecological analyses. After the increment cores being prepared according to standard procedures, the ring widths (total-ring and intra-ring widths) were measured with a WinDENDRO image-analysis system, and the measured tree-ring sequences were crossdated and quality-controlled with the software COFECHA. Using the software ARSTAN, we developed tree-ring width based chronology series of the four dominant conifers, eight site-specific Abies faxoniana chronologies, and seven site-specific chronologies of conifers in coniferous plantations and natural regenerated mixed stands. Mean sensitivities for total ring width chronologies of the four sampled dominant conifers were all below 0.2, while those for the latewood width chronologies of the same species were relatively much higher. Correlation coefficients between standard earlywood and total ring width chronologies of the four conifers were all above 0.9, but those between standard latewood and total ring width chronologies exhibited differences among species, with the coefficient of Larix potaninii the highest and that of Abies faxoniana the lowest. Correlation coefficients between latewood and total ring width of A. faxoniana obviously decreased from 1920-1970 for successive 50-year segments with 10-years lag analyses, though the same for the other three species changed unnoticeably with time. Tree-ring standard chronologies among species showed significant positive correlations, with the correlation coefficients between chronologies of Picea asperata and P. purpurea, and of Larix potaninii and Abies faxoniana relatively much higher. The first principal component of tree-ring chronologies represented the common radial growth patterns of the four conifers in Miyaluo area. The second, third and fourth PCs expressed the differences in radial growth responses for the genus Picea and Abies, for the evergreen and deciduous confers, and for the two species of the genus Picea, respectively. In general, mean sensitivities of the eight Abies faxoniana site-specific tree-ring width chronologies decreased with increasing altitude. The correlation coefficients between earlywood and total ring width chronologies for all sites reached 0.9, which did not change much with altitude; but those between latewood and total ring width chronologies diversified, with a decreasing tendency from lower altitudinal sites to higher altitudinal sites. Correlation coefficients among site chronologies varied considerably, with significant positive correlations among higher site chronologies, mixed results among lower site chronologies, and poor and insignificant correlations between chronologies of higher site and lower site. The first PC, which represents 37.5% of the total variance, reflected a common radial growth response at sites of different altitudes, and it showed a tendency of explaining more variance with increasing altitude. The second and the third PCs contributed to 24.5% and 18.2% of the total variance, respectively, exhibiting distinctive differences in radial growth responses between low- and high-altitudinal sites. With some exceptions, the radial growth represented by the second and third PCs had a positive correlation with that at the low-altitudinal sites and a negative correlation with that at the high-altitudinal sites. For those exceptional sites, factors other than altitude might also play a role in affecting tree-ring growth variations. Trees in stands of different altitudes showed great differences in frequencies of growth suppressions and releases through times, suggesting different disturbance histories and periods when trees recruiting to the canopy. Correlation coefficients between earlywood and total ring width chronologies for all sites of coniferous plantations and natural regenerated mixed stands were also above 0.9; and the same between latewood width and total ring width chronologies all positively correlated, too, with the coefficients of the coniferous plantations obviously much higher. Correlations among site chronologies showed that the coefficients among sites with similar stand origin and management regimes were much higher than those among sites with different stand origin and management regimes. For example, significant positive correlations were found for chronologies among different coniferous plantations, irrespective of species differences; while insignificant correlations between chronologies of the same conifer from a coniferous plantation and a natural regenerated mixed stand, and vise versa. Integrative comparisons of different tree growth parameters and radial growth rates at different stages indicated that the diameter at breast height (DBH) increments for trees in coniferous plantations were faster than those for trees of the same (or different) species in the natural regenerated mixed stands, at least within their first 40 years of stand development. Analyses of growth releases and suppressions, and basal area increments of trees in different stands demonstrated that over-dense individuals after canopy closure was the main factor resulting in high frequencies of radial growth suppressions, with some exceptions of severe man-made disturbances. Therefore, to ensure a continuous basal area current annual increment in certain periods, tree density controlling through thinning in due time during the stand development process are necessary. It should be mentioned that, as an introduced conifer to Miyaluo area, Larix kaempferi grew quite well at altitude of ca. 3100 m after planting in 1970s. In their near 30 years of stand development, Larix kaempferi trees exhibited faster growth in various parameters than Picea asperata trees of the similar stand age did. Thus we think it reasonable to use Larix kaempferi as a fast restoring species at appropriate sites of cutting blanks of subalpine coniferous forests in western Sichuan.

增温对川西亚高山针叶林不同光环境下几种幼苗生长的影响

由于人类活动所引起的地球大气层中温室气体的富集已导致全球地表平均温度在20 世纪升高了0.6 ¡æ，并预测在本世纪将上升1.4-5.8 ¡æ。气候变暖对陆地植物和生态系统产生深远影响，并已成为全球变化研究的重要议题。位于青藏高原东部的川西亚高山针叶林是研究气候变暖对陆地生态系统影响的重要森林类型。森林采伐迹地和人工云杉林下作为目前该区人工造林和森林更新的两种重要生境，二者截然不同的光环境对亚高山针叶林不同物种更新及森林动态有非常重要的影响。 本文以青藏高原东部亚高山针叶林几种主要森林树种为研究对象，采用开顶式增温法（OTCs）模拟气候变暖来研究增温对生长在两种不同光环境下（全光条件和林下低光环境）的几种幼苗早期生长和生理的影响，旨在从更新角度探讨亚高山针叶林生态系统不同树种对气候变暖在形态或生理上的响应差异，其研究结果可在一定程度上为预测气候变暖对亚高山针叶林物种组成和演替动态提供科学依据，同时也可为未来林业生产管理者提供科学指导。 1、与框外对照相比，OTCs 框内微环境发生了一些变化。OTCs 框内与框外对照气温年平均值分别为5.72 ¡æ和5.21 ¡æ，而地表温度年平均值分别为5.34 ¡æ和5.04 ¡æ，OTCs 使气温和地表年平均温度分别提高了0.51 ¡æ和0.34 ¡æ；OTCs框内空气湿度年平均值约高于框外对照，二者分别为90.4 %和85.3 %。 2、增温促进了三种幼苗生长和生物量的积累，但增温效果与幼苗种类及所处的光环境有关。无论在全光或林下低光条件下，增温条件下云杉幼苗株高、地径、分支数、总生物量及组分生物量（根、茎、叶重）都显著地增加；增温仅在全光条件下使红桦幼苗株高、地径、总生物量及组分生物量（根、茎、叶重）等参数显著地增加，而在林下低光条件下增温对幼苗生长和生物量积累的影响效果不明显；冷杉幼苗生长对增温的响应则与红桦幼苗相反，增温仅在林下低光条件下对冷杉幼苗生长和形态的影响才有明显的促进作用。 增温对三种幼苗的生物量分配模式产生了不同的影响，并且这种影响也与幼苗所处的光环境有关。无论在全光或林下低光环境下，增温都促使云杉幼苗将更多的生物量分配到植物地下部分，从而导致幼苗在增温条件下有更高的R/S 比；增温仅在林下低光条件下促使冷杉幼苗将更多的生物量投入到植物叶部，从而使幼苗R/S 比显著地降低；增温在全光条件下对红桦幼苗生物量分配的影响趋势与冷杉幼苗在低光条件下相似，即增温在全光条件下促使红桦幼苗分配更多的生物量到植物同化部分—叶部。 3、增温对亚高山针叶林生态系统中三种幼苗气体交换和生理表现的影响总体表现为正效应（Positive），即增温促进了几种幼苗的生理活动及其表现：（i）无论在全光或林下低光环境下，增温使三种幼苗的光合色素含量都有所增加；（ii）增温在一定程度上提高了三种使幼苗的PSII 光系统效率（Fv/Fm），从而使幼苗具有更强的光合电子传递活性；增温在一定程度使三种幼苗潜在的热耗散能力（NPQ）都有所增强，从而提高幼苗防御光氧化的能力；（iii）从研究结果来看，增温通过增加光合色素含量和表观量子效率等参数而促进幼苗的光合作用过程。总体来说增温对幼苗生理过程的影响效果与幼苗种类及所处的光环境有关，增温仅在全光条件下对红桦幼苗光合过程的影响才有明显的效果，而冷杉幼苗则相反，增温仅在低光条件下才对幼苗的生理过程有显著的影响。 4、增温对三种幼苗的抗氧化酶系统产生了一定的影响。从总体来说，增温使几种幼苗活性氧含量及膜脂过氧化作用降低，从而在一定程度上减轻了该区低温对植物生长的消极影响；增温倾向表明使三种幼苗体内抗氧化酶活性和非酶促作用有所提高，从而有利于维持活性氧代谢平衡。但增温影响效果与幼苗种类所处的光环境及抗氧化酶种类有关，增温对冷杉幼苗抗氧化酶活性的影响仅在林下低光环境下效果明显，而对红桦幼苗抗氧化酶活性的影响仅在全光条件下才有明显的效果。 总之，增温促进了亚高山针叶林生态系统中三种幼苗的生长和生理表现，但幼苗生长和生理对增温的响应随植物种类及所处的光环境不同而变化，这种响应差可能异赋予了不同植物种类在未来气候变暖背景下面对不同环境条件时具有不同的适应力和竞争优势，从而对亚高山针叶林生态系统物种组成和森林动态产生潜在的影响。 Enrichment of atmospheric greenhouse gases resulted from human activities suchas fossil fuel burning and deforestation has increased global mean temperature by 0.6¡æ in the 20th century and is predicted to increase it by 1.4-5.8 ¡æ. The globalwarming will have profound, long-term impacts on terrestrial plants and ecosystems.The ecoologcial consequences arising from global warming have also become thevery important issuses of global change research. The subalpine coniferous forests inthe eastern Qinghai-Tibet Plateau provide a natural laboratory for the studying theeffects of climate warming on terrestrial ecosystems. The light environment differssignificantly between clear-outs and spruce plantations, which is particularlyimportant for plant regeneration and forest dynamics in the subalpine coniferous forests. In this paper, the short-term effects of two levels of air temperature (ambient andwarmed) and light (full light and ca. 10% of full light regimes) on the early growthand physiology of Picea asperata, Abies faxoniana and Betula albo-sinensis seedlingswas determined using open-top chambers (OTCs). The aim of the present study wasto understand the differences between tree species in their responses to experimentalwarming from the perspective of regeneration. Our results could provide insights intothe effects of climate warming on community composition and regeneration behavior for the subalpine coniferous forest ecosystem processes, and provide scientificdirection for the production and management under future climate change. 1. The OTCs manipulation slightly altered thermal conditions during the growingseason compared with the outside chambers. The annual mean air temperature andsoil surface temperature was 5.72 and 5.34 ¡æ (within the chambers), and 5.21 and5.04 ¡æ (outside the chambers), respectively. The OTCs manipulation increased airtemperature and soil surface temperature by 0.51 and 0.34 ¡æ on average, respectively.Air relative humidity was slightly higher inside the OTCs compared with the controlplots, with 90.4 and 85.3 %, respectively. 2. Warming generally stimulated the growth and biomass accumulation of thethree tree species, but the effects of warming on growth and development variedbetween light conditions and species. Irrespective of light regimes, warmingsignificantly increased plant height, root collar diameter, total biomass, componentbiomass (stem, foliar and root biomass) and the number of branches in P. asperataseedlings; For A. faxoniana seedlings, significant effects of warming on all the tested parameters (plant height, root collar diameter, total biomass, and component biomass) were found only under low light conditions; In contrast, the growth responses of B.albo-sinensis seedlings to warming were found only under full light conditions. Warming had pronounced effects on the pattern of carbon allocation. Irrespectiveof light regimes, the P. asperata seedlings allocated relatively more biomass to rootsin responses to warming, which led to a higher R/S. Significant effects of warming onbiomass allocation were only found for the A. faxoniana seedlings grown under lowlight conditions, with significantly increased in leaf mass ratio (LMR) and decreasedin R/S in responses to warming manipulation. The carbon allocation responses of B.albo-sinensis seedling to warming under full light conditions were similar with theresponse of A. faxoniana seedlings grown under low light conditions. Warmingsignificantly decreased root mass ratio (RMR), and increased leaf mass ratio (LMR)and shoot/root biomass ratio (S/R) for the B. albo-sinensis seedlings grown under full light conditions. 3. Warming generally had a beneficial effect on physiological processes of dominant tree species in subalpine coniferous forest ecosystems: (i) Warming markedincreased the concentrations of photosynthetic pigments in both tree species, but theeffects of warming on photosynthetic pigments were greater under low lightconditions than under full light conditions for the two conifers; (ii) Warming tended toenhance the efficiency of PSII in terms of increase in Fv/Fm, which was related tohigher chloroplast electron transport activity; and enhance non-radiative energydissipation in terms of in increase in NPQ, which may reflect an increased capacity inpreventing photooxidation; (iii) Warming may enhance photosynthesis and advancephysiological activity in plants by increasing photosynthetic pigment concentration,the efficiency of PSII and apparent quantum yield (Φ) etc. From the results, theeffects of warming on seedlings’ physiological performance varied between lightenvironment and species. The effects of warming on photosynthesis performance of B.albo-sinesis seedlings were pronounced only under full light conditions, while thephysiological responses of A. faxoniana seedlings to warming were found only underthe 60-year plantation. These results provided further support for the observationsabove on growth responses of seedlings to warming. 4. Warming had marked effects on antioxidative systems of the three seedlings.Warming generally decreased H2O2 accumulation and the rate of O2- production, andalleviated degree of lipid peroxidation in terms of decreased MDA content, whichalleviated to some extent the negative effects of low temperature on the plant growthand development in this region; Warming tended to increase the activities ofantioxidative enzymes and stimulate the role of non-enzymatic AOS scavenging,which helped to create an balance in maintaining AOS metabolites for the threeseedlings. Nevertheless, the effects of warming on antioxidative defense systems werepronounced only under the 60-year plantation for the A. faxoniana seedlings. Incontrast, the marked effects of warming on antioxidative defense systems for the B.albo-sinesis seedlings were found only under the full light conditions. In sum, warming is considered to be generally positive in terms of growth andphysiological process. However, the responses of growth and physiology performanceto warming manipulation varied between species and light regimes. Competitive and adaptive relationships between tree species may be altered as a result of responsedifferences to warming manipulation, which is one mechanism by which globalwarming will alter species composition and forest dynamics of subalpine coniferousforest ecosystems under future climate change.

模拟增温对川西亚高山人工云杉林土壤碳含量和土壤呼吸的影响

全球气候变化已经成为不争的事实，其中全球变暖是近年来国内外的研究热点之一。土壤碳库作为陆地生态系统最大的碳库，气温升高必然会导致一系列的土壤碳储量和碳通量的变化，这些微小的变化又可能导致大气CO2浓度的变化并强化这种变暖的趋势。目前，土壤碳循环对温度升高的响应仍然是陆地碳循环研究最缺乏的部分，对土壤有机碳动态变化的研究仍存在着很大的不确定性与争议。四川西部的亚高山人工针叶林是青藏高原东部高寒林区的重要组成部分，是研究全球变化对森林生态系统影响的关键地区和重要森林类型。本研究通过采用原位人工模拟增温装置（Open-top chambers，OTCs）对川西米亚罗60年人工云杉林土壤实施增温，研究高海拔地区森林，尤其是人工森林系统下的土壤有机碳 含量、土壤呼吸及土壤酶活性对温度升高的响应。结果表明： 1. 增温处理的660天（2005年11月至2007年9月）期间，增温条件下的平均气温和土壤平均温度分别比对照提高0.43 ℃和0.27 ℃；0~10 cm土壤含水量在增温的不同时期均有不同程度的降低。 2. 土壤蔗糖酶、蛋白酶和脲酶活性在温度升高的不同阶段均有不同程度的提高。在增温处理300天（2006.09）、540天（2007.05）、600天（2007.07）和660天（2007.05）后，0~10 cm层的蔗糖酶活性分别比对照提高了36.36%（P<0.05）、24.31%、14.54%（P<0.05）和7.22%，脲酶活性分别提高了12.90%、24.19%（P<0.01）、34.48%（P<0.05）和14.64%(P<0.05)，蛋白酶活性分别提高了31.37%、1.99%、3.70%和17.80%。10~20 cm层的土壤酶活性也均有不同程度的提高，但均没有显著差异。蔗糖酶、脲酶和蛋白酶活性均呈现出随土层加深而减弱的趋势。 3. 土壤过氧化氢酶和多酚氧化酶活性在增温的第1年内均有不同程度的提高，但在增温的第2年内比对照有所降低。增温300天后（2006.09），过氧化氢酶和多酚氧化酶在0~10 cm层分别比对照增加3.76%和49.25%（P<0.05），10~20 cm层分别增加了5.54%和29.67%。在增温的第2年内，增温540天（2007.05）、600天（2007.07）和660天（2007.09）后，0~10 cm层的过氧化氢酶活性分别比对照降低了27.70%（P<0.05）、4.34%和1.47%，多酚氧化酶活性分别降低了5.86%、11.76%（P<0.05）和7.47%。增温的第2年内，10~20 cm层的过氧化氢酶和多酚氧化酶活性也均有不同程度的降低，但差异均未达到显著水平。不同土层之间相比较，过氧化氢酶活性随土层加深而降低，多酚氧化酶活性随土层加深而增加。 4. 土壤有机碳和有机质在增温的不同阶段，含量比对照均有所降低；且随增温时间的延长，降低的幅度下降。0~10 cm层的土壤有机碳和土壤有机质在增温300天（2006.09）、540天（2007.05）、600天（2007.07）和660天（2007.09）后分别降低了8.69%、4.35%、3.80%和2.44%，差异均未达到显著水平。土壤全氮含量在增温后与对照相比无明显的增加或者降低趋势。增温条件下的土壤C/N比与对照相比有所降低，但在增温各阶段的差异均不显著。10~20 cm层的有机碳、有机质和C/N比也有不同程度的降低趋势，但差异均不显著。不同土层之间相比，0~10 cm层的有机碳、有机质、全氮含量和C/N比均高于10~20 cm层，呈现出随土层加深而降低的趋势。 5. 土壤呼吸速率在增温第1年内，与对照相比明显提高，但在增温处理2年后，与对照相比无显著变化。增温300天（2006.09）和360天（2006.11）后分别提高了13.32%和21.17%，差异显著。增温处理540天（2007.05）到660天（2007.09）期间，与对照相比，不仅没有明显的提升，反而有些月份比对照有所降低，对温度升高的敏感性降低，呈现出对温度升高的适应性。土壤呼吸的日呼吸速率呈现单峰曲线形式，在14:00~20:00期间达到最大值，在4:00~10:00期间具有最低值。土壤呼吸的季节变化，呈现出与外界环境温度相一致的趋势，在7月份（夏季） 最高，11月份（冬季）最低。土壤呼吸与2 cm土壤温度、5 cm土壤温度和空气温度均呈极显著指数相关，与0~10 cm土壤含水量呈线性相关，相关性达到显著水平，但低于土壤呼吸与温度的相关性。 The past century has seen a marked increase in atmospheric carbon dioxide concentrations and a concomitant warming that has drawn scientific attention to the link between global carbon stocks and climate change. In particular, the decomposition and turnover of soil organic matter is recognised as an important determinant of carbon driven climate change. The slightly variation in soil organic carbon will result in the increase of atmospheric carbon dioxide concentrations and reinforce the tendency of warming. The experiment was conducted in Subalpine coniferous forest in western Sichuan province. Subalpine coniferous forest in western Sichuan was a important part of eastern Qinghai-Tibetan Plateau, which play a important role in reseaching the sensitivity of forest ecosystem to climate change. To investigate the effects of elevated temperature on soil organic carbon content, soil respiration rates, and soil enzyme activities in subalpine Picea asperata plantations, a esimulated warming measure was applied with Open-top chambers. The results were as followed: 1) During the period from Nov. 2005 to Sep. 2007, mean air temperature and soil temperature were respectively 0.43℃ and 0.27℃ the ambient higher. Soil water content decreased to different exent in different months in warmed plots than in unwarned plots at depth of 0-10 cm. 2) In general, elevated temperature enhanced the soil enzyme activities of invertase, protease, and urease. In the first year of warming—after 300 days’ treatment (in Sep,2006), the activities of invertase, protease, and urease increased by 36.36%, 12.90% and 31.37% respectively at the depths of 0-10 cm，among which the activity of invertase reached statistic significance. In the second year of warming, invertase activity increased by 24.31% after 540 days’ treament (in May, 2007), 14.54% after 600 days’ treament (in Jul, 2007) and 7.22% after 660 days’ treatment (in Sep, 2007) at the depths of 0-10 cm, and the differences in July and Septemmber were statistically significant. Elveated temperature also increased the activity of urease in the second year of warming and had significant effects in May and July. The activity of protease in warmed plots was also higher than in unwarmed plots at depths of 0-10 cm, but there was no significant difference. Elevated temperature had no significant effects on all soil enzyme acitivities at the depths of 10-20 cm in the first and sencond year. The values of above-mentioned soil enzyme all decreased with soil layers. 3) Eleavted temperature enhanced the activities of catalase and polyphenol oxidase in the first year of warming while they turned out downtrend in the second year. The activity of catalase increased by 3.76% and 5.54% at depths of 0-10 cm and 10-20 cm respectively in the first year—after 300 days’ warming (in Sep, 2006), the differences of which had no statistical significance. The activity of polyphenol oxidase was significantly increased by 49.25% at depths of 0-10 cm and not significantly increased by 29.67% at depths of 10-20 cm after 300 days’ warming. In the second year of warming, the catalase activity was significantly decreased by 27.70% after 540 days’ treament (in May, 2007) and not significantly decreased by 4.34% and 1.47% after 600 days’ (in Jul, 2007) and 660 days’ treament (in Sep, 2007) respectively. The activities of catalase and polyphenol oxidase at depths of 10-20 cm were decreased to different extent, but there was no significant difference. Catalase activity stepped down with soil layers while polyphenol oxidase activity stepped up. 4) Increased temperature in both the first year and the second year resulted tendency of decrease in the contents of soil organic carbon and soil organic matter, and C/N ratios at soil depths of 0-10 cm and 10-20 cm. However, with the prolonged warming, the tendency of decrease gradually tapered off and the extent of decrease in the second year of experiment were lower than that in the first year. The contents of soil organic carbon and soil organic matter were all decreased 8.69% by warming in the first year and dcreased 4.35%, 3.80% and 2.44% in May, July and September of the second year, but no significant difference were found. The C/N ratios increased 8.52% in the first year of warming and had less increment in the second year, all of which were not statistical significant. Eleveated temperature had no obvious effect on the content of tatol N in two year consecutive warming experiment. The contents of soil organic carbon and soil organic matter, total N and C/N ratios all had the tendency of dcreasing with soil layers. 5) Soil respiration rates were significantly enhanced by 13.32% and 21.17% after 300 days’ (in Sep, 2006) and 360 days’ (in Nov, 2006) treament in the first year of warming, but the same showed no obvious difference in the second year of treatment, which was assumed the adaptability of soil respiration with a certain heightened temperature. Diurnal soil resspiration showed a daily variation with a minimum value between 4:00 and 10:00 h and a maximum value between 14:00 and 20:00 h, coinciding with the minimum and maximum values of soil temperature at 2 cm. Soil respiration rates exhibited a pronounced seasonal variation with minimum values in Novmber and a maximum value in July, approximately coinciding with the seasonal variation of air and soil temperature. An exponential function provided the best fit for soil respiration with temperature while a quadric equation was used to estimate the effect of soil moisture on soil respiration, which were all significantly correlated. Soil respiraion rate was more highly correlated with the soil temperature than soil moisture.

次生植被土壤碳、氮养分季节动态及凋落物输入与温度的影响

土壤微生物量、可溶性有机碳与氮虽然只占土壤有机碳、氮总量的较小部分，但可以在土壤全碳、氮变化之前反映土壤微小的变化，又直接参与土壤生物化学转化过程，因而在植被恢复过程中，较其它土壤理化性质等能够更好地指示土壤恢复情况。在青藏高原东缘存在大面积的次生人工林替代灌丛或采伐迹地，而关于这些人工林替代后的生态效果和生态过程的评估却十分缺乏，本研究通过评估岷江上游植被恢复重建过程中典型人工替代次生植被凋落物层与土壤碳、氮等养分大小，动态监测土壤微生物生物量、水溶性碳、氮等指标，结合温度与凋落物输入等影响土壤活性有机碳、氮因子的控制试验，系统分析不同人工替代次生植被土壤碳、氮等养分的差异原因，试图寻找低效人工林优化调控与持续管理技术，为区域生态公益林持续管理提供理论和技术依据。主要结论如下： 1. 通过对不同人工替代次生植被凋落物层和土壤碳、氮分析发现，油松和华山松人工林替代次生灌丛后土壤碳、氮含量较灌丛和阔叶人工林低，主要原因可能为凋落物质量(C/N)较差，而引起碳、氮等元素难以归还土壤。进而通过对不同人工替代次生植被凋落物层和土壤微生物生物量、水溶性有机碳、氮等指标的季节性动态模式的分析，发现各次生植被土壤微生物生物量C、N，P以及土壤水溶性碳、氮含量均呈明显季节性动态，呈现秋季明显大于其它季节，冬季最低，在表层土壤最为明显。 2. 油松、华山松人工林凋落物层和土壤水溶性有机碳(WDOC)、土壤水溶性有机氮(WDON)明显低于灌丛和连香树，土壤微生物生物量C、N也以油松和华山松人工林最低，而落叶类植被，如灌丛、连香树和落叶松之间没有明显差异，说明可利用底物的数量和质量差异是影响各次生植被凋落物分解和土壤微生物活性的主要原因。MBC/OC和MBN/ON能较好地指示土壤微生物活性的变化，MBC/OC凋落层总体以灌丛和连香树人工林最高，油松和华山松人工林最低；而土壤中MBC/OC连香树人工最高，华山松人工林最低。说明以油松和华山松为主的人工造林替代乡土阔叶灌丛造成土壤C、N等养分严重匮乏，微生物活性低下是影响其养分周转的主要原因。 3. 从各次生植被凋落物产生看，凋落物年归还量最大的为华山松人工林(5.1×103 kg ha-1)，其次为落叶松人工林(4.8×103 kg ha-1)，阔叶灌丛林地凋落物产生总量(4.4×103 kg ha-1)略大于油松人工林(4.2×103 kg ha-1)，最小的为连香树人工林(3.6×103 kg ha-1)；叶是凋落物的主体，落叶类树种月动态表现为单峰型，高峰主要在10-11月，如落叶松、连香树和灌丛林；常绿的松类月动态不明显，各月基本相同，最为明显地为油松林，华山松人工林略有二个小峰，分别出现在11月和5月。落叶阔叶灌丛的凋落物分解速率大于常绿针叶林，如油松和华山松。结合凋落物的产生量和分解速率，不同树种人工林替代次生阔叶灌丛后，人工油松和华山松林枯落物总贮量和厚度明显大于落叶松人工林、灌丛林和连香树人工林，说明以油松和华山松为主的人工造林替代乡土阔叶灌丛延缓了有机物向土壤的顺利归还，不利于土壤C、N等养分循环。 4. 通过控制地面凋落物和地下根系输入有机物对土壤碳、氮的影响研究发现，(1) 单独去除根系以及根系与地面凋落物同时去除处理1年后对表层(0-10cm)土壤WDOC均没有显著影响，而土壤WDON显著增加，油松人工林土壤微生物生物量C、N显著降低，人工落叶松林没有显著差异，说明油松人工林土壤微生物活性对地下碳输入的依赖大于其它次生植被，而落叶松土壤微生物活性对地下碳输入依赖性较小；去除地面凋落物，明显降低了落叶松人工林土壤WDOC，华山松和连香树土壤WDON均较对照显著减少，油松人工林土壤微生物量C较对照显著减少；双倍增加地面凋落物处理对土壤微生物生物量、WDOC和WDON没有明显地增加，相反，连香树、华山松和油松人工林土壤WDON较对照减少。说明油松人工林微生物活性不仅依赖于地下碳输入，而且对地上有机物输入的依赖性也较大；连香树、落叶松和华山松人工林土壤微生物生物量并没有因地面凋落物的去除减少可能与土壤总有机碳含量及活性均较高有关，而双倍增加地面凋落物反而降低了土壤微生物生物量，说明凋落物覆盖后改变了土壤微气候。 5. 碳矿化累积量与有机碳含量和活性有机碳含量之间存在显著地正相关关系。凋落物碳累积矿化量、矿化速率以连香树最高，油松和华山松人工林次之，落叶阔叶灌丛低于常绿针叶纯林，导致其差异的主要原因可能为凋落物产生的时间动态模式不一样，致使凋落物起始分解时间不一致。而土壤层有机碳矿化速率和矿化量以阔叶落叶灌丛和连香树最高，油松和华山松人工土壤最低，再次证实利用针叶纯林恢复植被阻碍了有机质周转与循环。 6. 凋落物累积矿化量与C/N值呈显著地相关关系，并随着温度的升高而明显增加，而土壤累积矿化量与C/N值没有显著相关关系，说明土壤有机碳质量(C/N)对温度的响应不十分明显。通过双指数模型对不同温度下碳矿化过程进行模拟和计算出活性有机碳与惰性有机碳比例，发现温度升高促进了惰性有机碳向活性有机碳的转化，增加了活性有机碳含量，说明温度升高可促进次生植被凋落物与土壤有机质的分解，进而可影响到林地碳源/汇关系的变化。 综上，通过对不同人工替代次生植被凋落物与土壤C、N大小、以及土壤微生物生物量、水溶性C、N等指标动态变化模式研究，结合温度与凋落物数量输入等影响土壤活性C、N因子的综合分析，以油松和华山松人工纯林对山地植被恢复，延缓或阻碍了有机质周转与循环，造成了土壤肥力退化。对现有低效人工纯林改造，应为地面大量有机物分解创造条件。 Although soil microbial biomass, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) are a small part of total soil organic carbon and nitrogen, they can directly participate in the process of soil biochemical translation and indicate the fine changes before changes of soil total organic carbon and nitrogen occur. So, they are good indexes to indicate soil restoration condition during the process of vegetation rehabilitation. There are large areas of secondary vegetations which substitute for indigenous shrubs in the eastern fringe of Qinghai-Tibet Plateau. However, it is not well known that the ecological effect and process after substitution by different secondary plantations. Based on comparison of soil organic and nitrogen contents in litter layer and soil under different secondary vegetations in upper reaches of Minjiang River, soil microbial biomass, DOC and DON in litter layer and soil were investigated in order to analyze the seasonal dynamic. Combining the effects of temperature, litter input and root exclusion on soil microbial biomass, DOC and DON, we also aim to understand the reason and mechanism of difference in soil carbon and nitrogen contents among different secondary vegetations. The study would contribute to comprehensively understanding C and N cycling processes and provide optimal control and sustainable technology of low-effect plantations in these regions. The results are as follows: (1) Organic carbon and nitrogen in litter layers and soil under different substitution plantations were investigated. The results showed that contents of soil organic carbon and nitrogen were lower in P. tabulaeformis (PT) and P. armandi Franch(PA) than those in native broad-leaf shrub and broad-leaf plantation. The low quality (C/N) of litter in PT and PA plantations caused carbon and nitrogen returning to soil difficultly. Seasonal dynamic of soil microbial carbon (MBC),-nitrogen (MBN),-phosphor (MBP), and WDOC and WDON showed similar pattern, which had the highest values in autumn and the lowest values in winter. (2) WDOC and WDON in litter layers and soil under PT and PA plantations were significantly lower than those in native broad-leaf shrub and Cercidiphyllum japonicum Sieb. et Zucc.(CJ). Soil MBC and MBN were also the lowest, while there were no significant differences among deciduous vegetations, i.e. native broad-leaf shrub, CJ and Larix kaempferi Lamb.(LK) plantation. The results suggested that difference in quantity and quality of available substance was main reason that affected the activity of microbe in soil and litter layer. MBC/OC and MBN/ON were good indexes to indicate the change of soil microbial activity. MBC/OC of litter had the highest value under native broad-leaf shrub and CJ plantation, and had the lowest value in PT and PA plantations, while MBC/OC of soil was the highest under CJ plantation, and was the lowest in PT and PA plantations. These results indicated that PT and PA plantations substituting for native broad-leaf shrub caused deficit of carbon and nitrogen in soil, low microbial activity was a main reason influencing the cycling and turnover of carbon and nitrogen in soil. (3) The annual litter fall production, composition, seasonal dynamic and decomposition of five typical secondary stands in upper reaches of Minjiang River were studied in this paper. The annual litter productions were: PA (5.1×103 kg ha-1), LK(4.8×103 kg ha-1), native broad-leaf shrub (4.4×103 kg ha-1), PT(4.2×103 kg ha-1)，CJ(3.6×103 kg ha-1). The litter production of leaves in five secondary vegetations occupied a higher percentage in the annual total litter production than those of other components. The litterfall was mostly producted in the cool and dry period (October-November) for deciduous vegetations and relatively equably producted in every season for evergreen coniferous vegetations. The decomposition rate of leaf litter in the broad-leaf stand was higher than those in evergreen coniferous stand. Combined with annual litter fall production and decomposition rate of leaf litter, we found that stock and depth of litter layer were significantly larger in PT and PA plantations than those in native broad-leaf shrub, LK and CJ plantations. The results confirmed that PT and PA plantations substituting for native broad-leaf shrub delayed organic matter returning to soil and hindered cycling of carbon and nitrogen again. (4) We explored plant litter removal, double litter addition, root trenching, and combining root trenching and litter removal treatments to examine the effects of above- and belowground carbon inputs on soil microbial biomass, WDOC and WDON in four secondary plantations. During the experimental period from June 2007 to July 2008, 1 year after initiation of the treatments, WDOC in soil did not vary in root trenching, and combining root trenching and litter removal treatments, while WDON in soil significantly increased compared with CK treatment. Root trenching reduced soil MBC and MBN in PT plantation, while MBC and MBN in soil did not vary in LK plantation. The rasults implied that soil microbial activity was more dependent on belowground carbon input in PT plantation than those in other secondary plantations, on the contrary, soil microbial activity in LK plantation was not dependent on belowground carbon input. Plant litter removal significantly decreased soil WDOC in LK plantation, decreased WDON in PA and CJ plantations, and also significantly reduced soil MBC in PT plantation. However, double litter addition did not increase soil microbial biomass, WDOC and WDON, on the contrary, soil WDON in CJ, PA and PT plantations were decreased. These suggested that soil microbial activity was not only dependent on belowground carbon input, but also on aboveground organic material input. Double litter addition could change the microclimate and result in the decrease of soil microbial activity in CJ, PA and PT plantations. (5) We measured carbon mineralization in a 107 days incubation experiment in 5℃,15℃ and 25℃. Carbon cumulative mineralization was positively correlated with organic matter and labile organic carbon in litter layer and soil. Cumulative carbon mineralization and mineralization rate of litter layers in PT and PA plantations were higher than that in native broad-leaf shrub. This difference between native broad-leaf shrub and coniferous plantations in cumulative carbon mineralization and mineralization rate of litter layers could be attributed to the initiating time of decomposition due to the difference in seasonal dynamic of litter fall production between two types of secondary plantations. However, cumulative carbon mineralization and mineralization rate in soil were the highest in native broad-leaf shrub and CJ plantation, and were the lowest in PT and PA plantations. This also confirmed that PT and PA plantations substituting for native broad-leaf shrub hindered the cycling and turnover of organic matter again. (6) Carbon cumulative mineralization was positively correlated with C/N in litter layer and increased with temperature increasing, while carbon cumulative mineralization was not correlated with C/N in soil. This indicated that soil organic matter quality (C/N) was insensitive to temperature. Applying bi-exponential model, we computed the percent of labile and stable carbon in different temperature incubation and found that temperature increasing would accelerate the transform from stable carbon to labile carbon and increase the percentage of labile organic carbon. This illuminated that temperature incraesing could facilitate the decomposition of litter and soil organic matter in secondary vegetations and hence affect the relationship between carbon source and sink.

水分亏缺和凋落物水浸液对云杉幼苗生长和种子萌发的影响

在人类活动导致全球变暖的前提下，由于全球气温的升高，地表水分加速向空中蒸发。从20世纪70年代至今，地球上严重干旱地区的面积几乎扩大了一倍。这一增长的一半可归因于气温升高而不是降雨量下降，因为实际上同期全球平均降水量还略有增长。干旱对陆地植物和农林生态系统产生深远影响，并已成为全球变化研究的一个重要方面。位于青藏高原东部的川西亚高山针叶林是研究气候变暖对陆地生态系统影响的重要森林类型。森林采伐迹地、人工林下和林窗环境作为目前该区人工造林和森林更新的重要生境，其截然不同的光环境对亚高山针叶林更新和森林动态有非常重要的影响。凋落物产生的化感物质可通过影响种子萌发和早期幼苗的定居而影响种群的建立和更新，而人工林和自然林物种以及更新速度的差异性也都受凋落物的影响。 云杉是川西亚高山针叶林群落的重要树种之一,在维持亚高山森林的景观格局和区域生态安全方面具有十分重要的作用，其自然更新能力及其影响机制一直是研究的热点问题。本试验以云杉种子和2年生幼苗为研究对象，从萌发、根尖形态、幼苗生长、光合作用、渗透调节和抗氧化能力等方面研究了不同光环境下水分亏缺和凋落物水浸液对云杉种子和幼苗生长的影响。旨在从更新的角度探讨亚高山针叶林自然更新的过程，其研究成果可在一定程度上为川西亚高山针叶林更新提供科学依据，同时也可为林业生产管理提供科学指导。主要研究结论如下： 水分亏缺在生长形态、光合作用、抗氧化能力、活性氧化对云杉幼苗都有显著影响。总体表现为，水分亏缺导致了云杉幼苗的高度、地径、单株总生物量降低，增加了地下部分的生长；水分亏缺显著降低了云杉叶片中相对含水量、光合色素、叶氮含量，净光合速率和最大量子产量(Fv/Fm)，提高了幼苗叶片中膜脂过氧化产物（MDA）的含量；水分亏缺提高了幼苗叶片中过氧化氢(H2O2)含量，超氧荫离子（O2-）生成速率以及脯氨酸和抗氧化系统的活性（ASA, SOD, CAT, POD, APX和GR）。从这些结果可知，植物在遭受水分亏缺导致的伤害时，其自身会形成防御策略，并通过改变形态和生理方面的特性以减轻害。但是，这种自我保护机制依然不能抵抗严重水分亏缺对植物的伤害。 模拟林下低光照条件显著增加单株植物的地上部分生长，尤其是其叶片的比叶面积（叶面积/叶干重），同时其光合色素含量和叶片相对含水量也显著增加，这些改变直接导致植株光合速率和生物量的增加。同时，与高光照水平相比，低光照幼苗的膜脂过氧化产物（MDA）和活性氧物质均较低，显示出低光照比高光照水平对植物的更低的氧化伤害。尽管低光照也导致大部分抗氧化酶活性降低，但这正显示出植物遭受低的氧化伤害，更印证了前面的结论。 凋落物水浸液影响了云杉种子的萌发和根系的生长，更在形态、光合作用、抗氧化能力、活性氧物质以及叶氮水平上显著影响了云杉幼苗，其中，以人工纯林凋落物的影响更有强烈。具体表现在，种子萌发速率和萌发种子幼根的长度表现为对照>自然林处理>人工纯林；凋落物水浸液抑制种子分生区和伸长区的生长，人工林处理更降低了根毛区的生长，使根吸水分和养分困难。对2年生幼苗的影响主要表现在叶绿素含量、光合速率以及叶氮含量的降低；膜脂过氧化产物、活性氧物质和抗氧化酶系统的显著增加。同样的，人工纯林处理对云杉幼苗的影响显著于自然林处理。 在自然生态系统中，由于全球变暖气温升高导致的水分亏缺和森林凋落物都存在森林的砍伐迹地，林窗和林下环境中。我们的研究表明，与迹地或林窗强光照比较，林下的低光照环境由于为植物的生长营造了较为湿润的微环境，因此水分亏缺在林下对云杉幼苗造成的影响微弱。这可以从植物的形态、光合速率以及生物量积累，过氧化伤害和抗氧化酶系统表现出来。另一方面，凋落物水浸液在模拟林下低光照环境对植物的伤害也微弱于强光照环境，这与强光照环境高的水分散失导致环境水分亏缺有关；而人工纯林处理对云杉幼苗的伤害比对照和自然林处理显示出强烈的抑制作用。 Under the pre-condition of global warming resulted from intensive human activities, water in the earth’s surface rapidly evaporates due to the increase of global air temperature. From 1970s up to now, the area of serious drought in the world is almost twice as ever. This increase might be due to the increasing air temperature and not decreasing rainfall because global average rainfall in the corresponding period slightly is incremental. Drought will have profound impacts on terrestrial and agriculture-forest system and has also become the important issue of global change research. The subalpine coniferous forests in the eastern Qinghai-Tibet Plateau provide a natural laboratory for the studying the effects of global warming on terrestrial ecosystems. The light environment significantly differs among cutting blanks, forest gap and understory, which is particularly important for plant regeneration and forest dynamics in the subalpine coniferous forests. Picea asperata is one of the keystone species of subalpine coniferouis forests in western China, and it is very important in preserving landscape structure and regional ecological security of subalpine forests. The natural regeneration capacities and influence mechanism of Picea asperata are always the hot topics. In the present study, the short-term effects of two light levels (100% of full sunlight and 15% of full sunlight), two watering regimes (100% of field capacity and 30% of field capacity), two litter aqueous extracts (primitive forest and plantation aqueous extracts) on the seed germination, early growth and physiological traits of Picea asperata were determined in the laboratory and natural greenhouse. The present study was undertaken so as to give a better understanding of the regeneration progress affected by water deficit, low light and litter aqueous extracts. Our results could provide insights into the effects of climate warming on community composition and regeneration behavior for the subalpine coniferous forest ecosystem processes, and provide scientific direction for the forest production and management. Water deficit had significant effects on growth, morphological, physiological and biochemical traits of Picea asperata seedlings. Water deficit resulted in the decrease in height, basal diameter, total biomass and increase in under-ground development; water deficit significantly reduced the needle relative water content, photosynthetic pigments, needle nitrogen concentration, net photosynthetic rate and the maximum potential quantum yield of photosynthesis (Fv/Fm), and increased the degree of lipid peroxidation (MDA) in Picea asperata seedlings; water deficit also increased the rate of superoxide radical (O2-) production, hydrogen peroxide (H2O2) content, free proline content and the activities of antioxidant systems (ASA, SOD, POD, CAT, APX and GR) in Picea asperata seedlings. These results indicated that some protective mechanism was formed when plants suffered from drought stress, but the protection could not counteract the harm resulting from the serious drought stress on them. Low light in the understory significantly increased seedling above-ground development, especially the species leaf area (SLA), and photosynthetic pigments and relative needle content. These changes resulted in the increase in net photosynthetic rate and total biomass. Moreover, the lower MDA content and active oxygen species (AOS) (H2O2 and O2-) in low light seedlings suggested that low light had weaker oxidative damage as compared to high light. Lower antioxidant enzymes activities in low light seedlings indicated the weaker oxidative damage on Picea asperata seedlings than high light seedlings, which was correlative with the changes in MDA and AOS. Litter aqueous extracts affected seed germination and root system of Picea asperata seedlings. Significant changes in growth, photosynthesis, antioxidant activities, active oxygen species and leaf nitrogen concentration were also found in Picea asperata seedlings, and plantation treatment showed the stronger effects on these traits than those in control and primitive forest treatment. The present results indicated that seed germination and radicle length parameters in control were superior to those in primitive forest treatment, and those of primitive forest treatment were superior to plantation treatment; litter aqueous extracts inhibited the meristematic and elongation zone, and plantation treatment caused a decrease in root hairs so as to be difficult in absorbing water and nutrient in root system. On the other hand, litter aqueous extracts significantly decreased chlorophyll content, net photosynthetic rate and leaf nitrogen concentration of Picea asperata seedlings; MDA, AOS and antioxidant system activities were significantly increased in Picea asperata seedlings. Similarly, plantation treatment had more significant effect on Picea asperata seedlings as compared to primitive forest treatment. In the nature ecosystem, water deficit resulted from elevating air temperature and litter aqueous extract may probably coexist in the cutting blank, forest gap and understory. Our present study showed that water deficit had weaker effects on low light seedlings in the understory as compared to high light seedlings in the cutting blank and forest gap. The fact was confirmed from seedlings growth, gas exchange and biomass accumulation, peroxidation and antioxidant systems. This might be due to that low light-reduced leaf and air temperatures, vapour-pressure deficit, and the oxidative stresses can aggravate the impact of drought under higher light. On the other hand, litter aqueous extracts in the low light had weaker effects on the Picea asperata seedlings than those at high light level, which might be correlative to the water evapotranspiration under high light. Moreover, plantation litter aqueous extracts showed stronger inhibition for seed germination and seedling growth than control and primitive forest treatments.

川西亚高山森林生态系统辐射传输研究

辐射传输研究是贯穿森林生态系统的纽带，太阳辐射为植物的生长发育提供光合能量、适宜的环境温度以及发育信息。一方面，气候变化使到达地面辐射能的质和量发生变化，影响到植被的生长发育，改变森林的结构，而森林结构的变化又会影响林冠内辐射能的分配和质量，这些变化会进一步影响到林下土壤温度，改变森林根系活性以及土壤营养转化的效率；连锁反应的结果有可能会使森林生态系统的生产力发生变化，改变碳素和氮素源库的调节方向，从而反馈影响地球气候系统。另一方面，人类作为生态系统的成员，必然需要森林生态系统为其提供更多的原材料和更好的生态服务功能，如何实现这些目标，就需要人类适度调整干预方式和频度，达到预期的目的。本文在建立适合于川西亚高山森林的叶面积测量技术、光照辐射模型和土壤温度变化模型的基础上，对川西亚高山地带森林生态系统的辐射传输特征进行了分析，并从森林结构的角度探讨了林分内的辐射分布以及对土壤温度的影响。主要成果如下： 1. 提出了一种照相法测量叶面积的方法。通过对摆放在平面上的叶片照相，利用投影变化，把非正射图像转化为正射图像，然后经过计算机图像处理得到每一片叶片的面积、周长、长度、宽度等信息。这种方法可使用户以任意方向和距离拍摄处于平面上的叶片，能同时处理大量的叶片，适于野外离体或活体叶片测量。叶片面积分辨率可调，分辨率可以与常用的激光叶面积仪相近甚至更高，而且叶片图像可以存档查询。 2. 提出一种模拟林内光照变化的模型。利用林冠半球照片，记录视点以上半球内的林冠构件空间分布，作为林冠子模型；天空辐射子模型采用国际照明委员会(CIE)的标准晴天和阴天以及插值模型。该模型能够模拟林下某一位点处的实时光斑变化。 3. 提出一种土壤温度变化模型。把土壤视为具有容量和阻力性质的结构，利用电阻和电容器件构建土壤能量分布模型。外界太阳辐射能经过植被以及其它一些能量分配器后进入土壤，其中有一部分转化为土壤势能，即土壤温度。土壤温度的变化类似于电池的充放电过程。在已知模型参数的情况下，可以从太阳辐射计算土壤温度的变化。在模型参数未知的情况下，通过输入和输出值推算模型的参数，而模型参数中的时间常数与土壤组成和含水量有关，这样就可以知道土壤水分的变化情况。 4. 从王朗亚高山森林典型样地林分结构的测量获得林地三维结构图、树冠形态、叶面积密度等参数，这些参数输入到Brunner (1998)开发的tRAYci 模型中计算出一段时间内林分任意位置处的光照值。与林下辐射计测量值以及半球照片计算结果的比较，该模型基本上能够满足对林分光环境了解的要求。 5. 从川西亚高山森林生产力的角度，探讨了森林生产力研究的方法以及川西地区的研究历史和成果，发现了其中的一些规律和问题，特别是在叶面积测量上，还没有使用标准的叶面积指数定义。综合来看，川西地区针叶林叶面积指数(单位土地面积上植物冠层总叶面积的一半) 应在4-5 之间。降雨丰富的华西雨屏带是川西地区森林生产力最高的地区，而向西北森林生产力逐渐降低。川西地区云冷杉林森林生产力平均约为600 gDM m-2 a-1，但是根据辐射能计算的潜在生产力则达到1800 gDM m-2 a-1。实际与潜在森林生产力的巨大差异说明其它因子对生产力的影响。 6. 王朗亚高山3 个典型森林林分中，白桦林样地(BF) 林下草本以糙野青茅、牛至、紫菀等喜阳性物种为主，林下透光度较高；冷杉林样地(FF) 林下透光度最低，以喜阴性物种水金凤、蟹甲草、囊瓣芹等为主；而云杉林样地(SF)林分林龄最大，林下透光度介于冷杉林和白桦林之间，草本层仍然以喜阴性物种东方草莓、紫花碎米芥、酢浆草等为主。冷杉林和云杉林的灌木层也很丰富，卫矛属、五加属、茶藨子属、忍冬属植物很丰富，而在白桦林则以栒摘要子属、榛子属、鹅耳枥属等植物为主。藓类植物在云杉林中最丰富，并且形成毯状层，其它两个林分则很稀少。3 个样地林分结构与林下光环境有很强的相关性，从光环境特征可以在一定程度上推测林分的结构。各样地单纯从乔木层材积推算的NPP 排列顺序为BF>FF>SF，与林下辐射透射率和林分年龄的顺序相同，暗示辐射对群落演替过程的驱动作用。 7. 用半球照相法测得BF、FF 和SF 3 个样地的有效叶面积指数以SF 样地最高，BF 最低。如果考虑针叶树叶片在小枝上的丛聚分布，利用北方针叶林的数值进行校正，则SF 样地LAI 显著增加(达到89%)，其它样地的LAI 基本不变甚至有所下降。校正后的数值与文献中地面测量的结果较相近，说明在使用半球照相法测量川西亚高山针叶林LAI 时必须加以校正。 8. 在3 个样地中，白桦、岷江冷杉和方枝柏种群为丛聚分布，紫果云杉在FF和SF 样地中基本上为随机分布。3 个物种出现丛聚分布的最短距离约为2m，在最短距离以内则为随机分布。最短距离可能与树冠大小有关，种子传播特征以及对光照的需求状况可能是造成这种分布格局类型的原因。 Radiative transfer plays a key role in forest ecosystems. Solar radiation providesenergy for photosynthesis, appropriate ambient temperature and development informationfor plants. However, quality and quantity of radiation reaching land surface are affected byweather and subsequently influence the growth and development of plants, which in turnchanges the budget of radiation in forest. Soil temperature changes with the variation ofradiation under forest canopy and influences the activity of roots and rate of nutrientturnover. Thus, any changes of radiation will induce chain reactions in the entireecosystem and display in the value of net primary productivity which will possibly shiftthe relationship between carbon source and sink at local or regional scale and feed back tothe global climate system. On the other hand, as a component of ecosystems, humanbeings of course need to demand more materials and better service from ecosystems. Forthese purpose, man must adapt their pattern and frequency of interference to ecosystems.This paper aims to research on the canopy structure, the radiation distribution and theirinfluence on soil temperature from the process of radiative transfer in subalpine forestecosystem of western Sichuan. The main results are: 1 Present a new photogrammetric method for leaf area. The main idea is to convertnon-vertically taken images of planar leaves to orthoimages through projectivetransformation. The resultant images are used to get leaf morphological parametersthrough image processing. This method enables users to take photos at almost anyorientation and distance if only the leaves are placed on same plane, and to processlarge quantity of leaves in a short time, which is suitable for field measurement. Theresolution of leaf area is adjustable to fit for special requirement. 2 A model using hemispherical photos combining with solar tracks and radiation courseis provided to simulate light variation in forest. The hemispherical photos of canopyrecord the real spatial distribution of each element of plants viewed from a point. Skyradiance is simulated with CIE standard clear sky or cloudy sky model. This modelcan be used to simulate real time light variation under canopy. 3 Present a soil temperature model. Soil could be regarded as a body of resistor andcapacitor. Some of the budget of solar radiation in soil body is transformed into soilpotential energy, the soil temperature. Variation of soil temperature is driven by solarradiation, vegetation, soil properties, etc. This model has two parameters, one of whichis time constant and is related to soil water content. The inversed model can be used tosimulate the variation of soil water. 4 By using model tRAYci developed by Brunner (1998), the 3-D distribution of light inthree subalpine forest stands of Wanglang Nature Reserve has been simulated andvalidated with value of radiometers in these stands. This model can basically satisfythe need for understanding light regimes of these stands. 5 Present some principles and questions of NPP (net primary of productivity) researchesin western Sichuan. The standard leaf area index (LAI) defined by Chen and Black(1997) has not been used in this region. Total leaf area and projected leaf area indexare still used in NPP researches which may differ around 1-fold in magnitude. Thestandard LAI which is a half of total leaf area above unit land area should be between4 and 5 for typical subalpine coniferous forest of western Sichuan concluded fromliteratures. The maximum forest NPP occurs in West China rain belt and decreasesnorthwestwards. Average NPP of spruce-fir forest in western Sichuan is about600gDM m-2 a-1, which is below the potential NPP of 1800gDM m-2 a-1 based onmeasured radiation in this region. The significant difference between potential and realNPP suggests that other factors influence the growth of stands. 6 In the three subalpine forest stands of Wanglang Nature Reserve, herbage layer ofAbstractbirch stand (BF) with age of 40 is dominated by heliophytes of Deyeuxia scabrescens,Origanum vulgare, Aster tongoloa etc.. However, both of the other two stands aredominated by shade tolerent species, such as Impatiens noli-tangere, Impatiensdicentra, Cacalia deltophylla and Pternopetalum tanakae etc. in fir stand (FF) withage of 180 and Fragaria orientalis, Cardamine tangutorum and Oxalis corniculata etc.in spruce stand (SF) with age of 330. Shrub species in the latter two stands arerelatively rich, typical dominant genera being Euonymus, Acanthopanax, Ribes andLonicera. Birch stand has relatively sparse shrubs dominated by genera of Cotoneaster,Corylus and Carpinus. Mosses are significant only in spruce stand. The canopystructure controls the light regime of stand, which influence the composition of herblayers beneath the canopy. This light regime-community structure relationship can beused to infer the herb community from canopy structure. The NPP derived from timbervolume of arbor layer of the three stands decreases from BF to SF, which is in thesame order of transmitted total radiation under canopy and age of these stands,suggesting the driving effect of radiation in the succession of community. 7 The highest effective LAI of the three stands obtained by hemispherical photos is inplot SF and lowest in plot BF. After rectification of the clumping effect of leaves onshoot, the real LAI in plot SF increases significantly (89%) and approximate to theaverage LAI of coniferous forest in western Sichuan. Therefore, the LAI obtainedfrom hemispherical photos needs rectification for clumping effect. 8 Spatial distribution pattern for Betula platyphylla, Abies faxoniana and Sabinasaltuaria is clumpy, but Picea purpurea almost random in plot FF and SF. The shortestdistance for clumpy distribution for Betula platyphylla and Sabina saltuaria is 1.5m,and 2m for Abies faxoniana. And random pattern for these trees is exhibited within thisrange which almost coincides with the diameter of crown. Seed dispersalcharacteristics and light requirement may be the reason for different spatial pattern.

模拟增温与UV-B 辐射增强对云杉种子萌发和幼苗生长的影响

臭氧层损耗导致的地球表面UV-B辐射增强以及温室气体增多引起的气候变暖是当今两大全球环境问题。UV-B辐射增强和气候变暖对陆地植物和生态系统产生深远影响，并已成为全球变化研究的重要议题。作为世界第三极的青藏高原，UV-B 辐射增强以及气候变暖现象尤为突出。本试验所在林区是青藏高原东缘的主要林区，具有大面积的亚高山人工针叶成熟林，在全球变化背景下该森林的天然更新潜力如何是急待回答的重要问题。基于此，本研究围绕森林树种的种子和幼苗这一更新的重要阶段，开展了气候变暖、UV-B辐射增强和联合胁迫对云杉种子萌发及幼苗定居影响的研究，旨在全球变化背景下，探讨全球变暖、UV-B 辐射增强和联合胁迫是否对西南地区大面积人工亚高山针叶林更新的种子萌发和幼苗定居阶段产生影响。 本文以青藏高原东缘亚高山针叶林主要树种云杉为研究对象，研究云杉种子萌发及幼苗的生长和生理对UV-B辐射增强与气候变暖的响应。采用UV-B荧光灯（UV-lamp）来模拟增强的UV-B 辐射，此外，采用开顶式有机玻璃罩（OTCs）来模拟气候变暖。本试验包括四个处理：（1）大气UV-B 辐射+大气温度（C）；（2）大气UV-B 辐射+模拟气候变暖（W）；（3）增强的UV-B辐射+大气温度（U）；（4）增强的UV-B辐射+模拟气候变暖（U+W）。 根据本试验结果，UV-B辐射增强对云杉种子萌发没有显著影响，它对萌发云杉幼苗的影响主要体现在幼叶展开以后。根据两年的试验结果，增强的UV-B辐射降低了云杉幼苗抗氧化酶活性，降低了抗氧化物质的含量，此外，造成了膜质的过氧化，表现为MDA在针叶中的积累。增强的UV-B照射处理萌发云杉幼苗两年后，幼苗的生长受到显著抑制。我们的结果显示，OTCs分别提高了空气（10 cm）和土壤（5 cm）温度1.74℃和0.94 ℃。增温显著地促进了云杉种子提前萌发，提高了萌发速率和萌发比率，而且，明显地促进了幼苗的生长，表现为株高和生物量累积的显著增长。此外增温还有利于云杉幼苗根的伸长生长以及生物量的累积，这可以使云杉幼苗更好地利用土壤中的水分和营养元素。 根据本试验结果，温度升高显著地促进了增强UV-B辐射下云杉萌发幼苗的生长，这说明，温度升高缓解了UV-B辐射增强对云杉萌发幼苗的负面影响。这种缓解作用可能是温度升高对UV-B辐射增强处理下幼苗的抗氧化系统活性改善的结果。温度升高还缓解了高UV-B辐射对云杉幼苗根生长的抑制作用，这也可能是增温缓解伤害的原因之一。此外，根据我们的试验结果，增温与UV-B辐射增强联合作用（U+W）下云杉萌发幼苗的生长状况好于大气温度与大气UV-B辐射联合（C）处理，表现为株高、地径、根长和生物量积累均高于C处理，因此可以推断，UV-B辐射增强与气候变暖同时存在对萌发幼苗在两年之内的生长没有产生抑制作用，也就是说，气候变暖的缓解作用完全弥补了UV-B辐射增强的有害作用。 同样，增强的UV-B辐射显著影响了云杉幼苗的光合作用，表现为净光合速率（Pn）和表观量子效率（Φ）的提高，此外，根据我们的试验结果，它还造成了PSII的光抑制。增强的UV-B辐射显著抑制了云杉幼苗对营养元素的吸收，表现为大量营养元素、碳、钙、镁和锌含量的降低，但是，它却显著促进了铁在植株体内的积累。增温显著地提高了净光合速率，但是，它对光系统II（PSII）的光化学效率影响不大。温度升高缓解了UV-B增强对云杉幼苗光合作用的伤害，表现为净光合速率、表观量子效率以及PSII光化学效率的提高。此外，温度升高还缓解了UV-B辐射增强对离子吸收的抑制作用。 Enhanced UV-B radiation due to the reduction of O3 layer and global warming induced by increased greenhouse gases in the air have become the two pressing aspects of global climate changes. Moreover, enhanced UV-B radiation and warming have profound and long-term impacts on terrestrial plants and ecosystems, and the studies focusing on the two factors have attracted many attentions. Qinghai-Tibetan Plateau is the third in elevation in the world, and enhanced UV-B radiation and climate warming are especially prominent in this region. Our research located in the main forest belt in the eastern Qinghai-Tibetan Plateau where large areas of subalpine coniferous forests distributed. Based on that, we carried out a research to study the effects of enhanced UV-B radiation and climate warming on seed germination and seedlings growth of seedlings which are the important basic stage in forest regeneration. This research was arranged by a complete factorial design and included two factors (UV-B radiation and temperature) with two levels. The UV-lamps were used to manipulate the supplemental UV-B radiation and open-top chambers (OTCs) were adopted to increase temperature. The four treatments were: (1) C, ambient UV-B without warming; (2) U, enhanced UV-B without warming; (3) W, ambient UV-B with OTCs warming; (4) U+W, enhanced UV-B with OTCs warming. The main results were exhibited as follows: 1. Based on our results in this research, OTCs increased temperature on average 1.74℃ in air (10 cm above ground) and 0.92 ℃ in soil (5 cm beneath ground). Furthermore, OTCs also slightly reduced soil moisture and relative air humidity, however, the differences was not statistically significant. 2. Our results showed that enhanced UV-B had no significant effects on the seeds germination of P. asperata. Enhanced UV-B affected sprouts of P. asperata until the needles unfolded. During two years, enhanced UV-B inhibited the efficiency of the antioxidant defense systems, and as a result, it induced oxidant stress and the accumulation of MDA in needles. After two years of exposure to enhanced UV-B, the growth of P. asperata sprouts was markedly restrained compared with those under ambient UV-B radiation and temperature (C). Warming significantly stimulated the germination speed and increased the germination rate of P. asperata seeds. In the next place, it prominently facilitated the growth of P. asperata sprouts, represented as improvements in stem elongation and biomass accumulation. Furthermore, warming also increased root growth of P. asperata sprouts, which could made sprouts more efficient to use water and nutrient elements in soil. In this research, warming alleviated the deleterious effects of enhanced UV-B on P. asperata sprouts. It markedly stimulated the growth of P. asperata sprouts exposed to enhanced UV-B. The ease effects of warming on the abilities of the antioxidant defense systems might account for its amending effects on growth. After two years of exposure to enhanced UV-B radiation and warming, the growth of P. asperata sprouts was better than those under ambient UV-B radiation without warming (C), which could be seen from the higher plant height, basal diameter, root length and total biomass accumulation compared with C. 3. Enhanced UV-B radiation significantly influenced the photosynthesis processes of two-year old P. asperata seedlings. Our results showed that enhanced UV-B reduced the net photosynthetic rate (Pn) and the apparent quantum efficiency (Φ), and induced photoinhibition of photosynthetic system II (PSII). Enhanced UV-B significantly decreased the concentration of nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg) and zinc (Zn), however, it increased the accumulation of iron (Fe) in the whole plant of P. asperata seedlings. Warming significantly stimulated Pn of P. asperata seedlings but it had no prominent impacts on the photochemical efficiency of PSII. In our research, warming also alleviated the harmful effects of enhanced UV-B on photosynthesis and absorption of ions of P. asperata seedlings. It increased Pn, Φ and the photochemical efficiency of PSII in seedlings exposed to enhanced UV-B. Moreover, warming also increased the absorption of ions of the seedlings exposed to enhanced UV-B radiation.

川西亚高山两种针叶树幼苗对增温和施氮的响应

人类活动引起全球大气中温室气体（CO2、CH4、NOx）浓度不断增加，致使地球表面温度在过去的100 年中已经增长了0.74 ± 0.18℃，预计到本世纪末将会增加1.1-6.4℃。此外，氮沉降也是当今社会的重要环境问题，随着经济发展的全球化, 高氮沉降也呈现出全球化趋势。全球气候变暖和氮沉降给陆地生态系统的地上、地下生物学和生物地球化学过程所带来巨大影响越来越引起人们的关注。 本文以川西亚高山针叶林的两个重要树种云杉和油松幼苗为研究对象，采用红外辐射增温（空气增温2.1℃，土壤增温2.6℃）和根部施氮（施氮量25 g N m-2yr-1）的方法，从生长形态、光合作用、抗氧化能力和矿质营养等方面研究这两种幼苗对气候变暖和氮沉降的响应。该实验为室外控制实验，包括四个处理：(1)不增温+不施氮（UU）；(2) 不增温+施氮（UF）；(3) 增温+不施氮（WU）；(4) 增温+施氮（WF）。本研究旨在从生理生化、物质代谢 、生长及形态等不同水平上研究模拟增温和施氮对两种树苗的联合效应，提高我们对全球变化下亚高山针叶林早期更新过程的理解，同时也为森林管理提供科学依据。具体研究结果如下： 单独增温处理显著提高了云杉和油松幼苗的地茎、叶重、茎重、根重以及总生物量；单独施氮处理也增加了两种幼苗的株高和总生物量。而增温和施氮联合作用对两种幼苗生长的影响并不相同，联合作用对云杉幼苗生长指标的正效应显著低于单独施氮处理，但是联合作用比单独增温或施氮更大程度的促进了油松幼苗生物量的积累。 单独增温和施氮都有利于提高云杉和油松叶片中叶绿素含量、净光合速率(A)、最大净光合速率(Amax)、表观量子效率（Φ）、最大光能转化效率（Fv/Fm）和量子产量（Y）。与对两种幼苗生长指标的影响相似，加氮和增温共同作用下油松幼苗的以上光合指标比在单独增温或施氮处理下有更大程度的提高；而联合作用下云杉幼苗叶绿素含量、净光合速率、最大净光合速率、表观量子效率、最大光能转化效率以及量子产量比单独施氮处理明显地降低。 增温和施氮都显著地降低了云杉和油松幼苗针叶组织中活性氧和丙二醛的积累。交互作用降低了云杉幼苗叶片的抗氧化酶活性、脯氨酸和ASA 的含量，却显著提高了油松幼苗SOD、POD、APX 等抗氧化酶的活性，并且对油松幼苗脯氨酸和ASA 积累的促进作用比单一因子更加明显。因此，增温和施氮共同作用下油松幼苗叶片中O2-产生速率、H2O2 及MDA 含量明显降低，而云杉叶片中只有O2-产生速率出现降低趋势。 增温和施氮都降低了云杉体内的P、Ca、Mg 元素的含量，增加了Cu、Zn、Mn 在各器官内的积累。对油松幼苗而言，增温和加氮单独作用也显著降低了Ca 含量增加了Cu、Zn、Mn 的积累，但是不同于云杉幼苗的是P、Mg 也显著增加。增温和施氮联合作用对云杉幼苗体内元素的影响与单一施氮处理或增温处理相似，不同的是比单一因子作用更为明显降低了P、Ca、Mg 含量，增加了植株中N、Cu、Zn、Mn 的含量，但是油松矿质元素含量在联合作用下并没有产生类似于云杉幼苗的双因子叠加效应。 总之，尽管单独增温或者施氮都有利于云杉和油松幼苗生长指标、光合能力以及抗氧化能力的提高。但是，增温和施氮对云杉幼苗生长生理的促进效应非但没有在交互作用下有更大的提高，反而低于单独氮处理。与此不同的是，增温和施氮联合作用比单因子作用更有利于油松幼苗生长及生理指标的提高。 With the continued increase in atmospheric concentrations of greenhouse gases (CO2、CH4、NOx), the mean global surface temperature has increased by about 0.74 ± 0.18℃ over the past century and is predicted to rise by as much as 6.4℃ during this century. Besides global warming, nitrogen deposition is another serious environmental problem caused by human activities, and high nitrogen load has become globalization as a result of global economy development. Global climate warming and nitrogen deposition have induced dramatic alternations in above - and below- ground biology and biogeochemistry process in terrestrial ecosystems, and more and more attention has been invited to those problems. This experiment mainly studies two important species Picea asperata and Pinus tabulaeformis in subalpine coniferous forest of western Sichuan, China. Infared heaters are induced to increase both air and soil temperature by 2.1℃ and 2.6 ℃, respectively. Ammonium nitrate solution (for a total equivalent to 25 g N m-2 year-1) is added to soil surface. There are four treatments in this study: (1) unwarmed unfertilized (UU); (2) unwarmed fertilized (UF); (3) warmed unfertilized (WU); (4) warmed fertilized (WF). This study is conducted to determine the influences of experimental warming and nitrogen fertilization on physiolchemistry, nutrition metabolism, growth and morphology in the two coniferous species seedlings. The current study is favorable for increasing our understanding on the early phase of regeneration behavior in subalpine coniferous forest, and it also provide scientific direction for forest management under future global changes. The results are as follows: Artificial warming alone significantly increased basal diameter, leaf mass, stem mass, root mass and total biomass for Picea asperata and Pinus tabulaeformis seedlings, and single nitrogen fertilization are also favorable for growth of the two species and stimulate plant hight and total biomass. The two species seedlings respond differently to the combination of elevated temperature and nitrogen addition. Warming combined with nitrogen fertilization weakens the positive effects of nitrogen addition for growth of Picea asperata seedlings. However, the combination of elevated temperature and nitrogen fertilization further increase biomass accumulation of Pinus tabulaeformis seedlings. Both elevated temperature alone and nitrogen fertilization alone can increase photosynthetic pigments contents, net photosynthetic rate (A), maximum net photosynthetic rate (Amax), apparent quantity yield (Φ), maximum photochemical efficiency of photosystem II (Fv/Fm) and effective quantum yield (Y). Similarly with growth parameters, the combination of warming and nitrogen addition induced more increment of these above photosynthetic parameters for Pinus tabulaeformis seedlings. However, these photosynthetic parameters of Picea asperata seedlings under the combination of warming and nitrogen addition are lower than those under nitrogen fertilization alone. The levels of active oxygen species (AOS) and malodiadehyde (MDA) in needles of the two coniferous species seedling are obviously decreased by experimental warming or additional nitrogen. Warming combined with nitrogen fertilizer reduces the activities of SOD, CAT and APX, and the contents of proline and ASA of Picea asperata seedlings, but the combination significantly increases activities of these antioxidant enzymes in needlels of Pinus tabulaeformis seedlings and further improves the accumulation of proline and ASA compared to either artificial warming or nitrogen addition. Therefore, the rate of O2 - production, the contents of H2O2 and MDA in needles of Pinus tabulaeformis seedlings are remarkably reduced by the combination of warming and nitrogen addition, but the combination only significantly decreased the rate of O2 - production of Picea asperata seedlings. Elevated temperature or nitrogen fertilization decrease the contents of P, Ca, Mg but increase Cu, Zn, Mn contents for Picea asperata seedlings. For Pinus tabulaeformis seedlings, elevated temperature alone and nitrogen fertilization alone decreased Ca, but increased P, Mg, Cu, Zn, Mn contents. The effects of the combination of warming and nitrogen addition on these element contents in needles of Picea asperata seedlings are added or multiplied the effects of warming and nitrogen addition alone, resulting in less contens of P, Ca, Mg and more contents of Cu, Zn, Mn than either elevated temperature or nitrogen fertilization. Howere, these adding or multipluing single-factor effects on contents of these elements are not observed in the case of Pinus tabulaeformis seedlings. In conclusion, growth parameters, photosynthetic capacities and antioxidant abilities of Picea tasperata and Pinus abulaeformis seedlings are improved by experimental warming or nitrogen fertilization. Interestingly, the positive effects of warming and nitrogen addition on growth and physiological performances are not multiplied by the combination of elevated temperature and nitrogen fertilization, even dempened for Picea asperata seedlings. However, for Pinus tabulaeformis seedlings, growth and physiological performances are further improved by the combination.

Carbon dioxide exchange between the atmosphere and an alpine meadow ecosystem on the Qinghai-Tibetan Plateau, China

We used the eddy covariance method to measure the M exchange between the atmosphere and an alpine meadow ecosystem (37degrees29-45'N, 101degrees12-23'E, 3250m a.s.l.) on the Qinghai-Tibetan Plateau, China in the 2001 and 2002 growing seasons. The maximum rates Of CO2 uptake and release derived from the diurnal course Of CO2 flux (FCO2) were -10.8 and 4.4 mumol m(-2) s(-1), respectively, indicating a relatively high net carbon sequestration potential as compared to subalpine coniferous forest at similar elevation and latitude. The largest daily CO2 uptake was 3.9 g cm(-2) per day on 7 July 2002, which is less than half of those reported for lowland grassland and forest at similar latitudes. The daily CO2 uptake during the measurement period indicated that the alpine ecosystem might behave as a sink of atmospheric M during the growing season if the carbon lost due to grazing is not significant. The daytime CO2 uptake was linearly correlated with the daily photosynthetic photon flux density each month. The nighttime averaged F-CO2 showed a positive exponential correlation with the soil temperature, but apparently negative correlation with the soil water content. (C) 2004 Elsevier B.V. All rights reserved.

Invasive alien species disrupt spatial and temporal ecology and threaten extinction in an insular, small mammal community

The impact of invasive bank vole (Myodes glareolus) and greater white-toothed shrew (Crocidura russula) on indigenous Irish small mammals, varies with season and habitat. We caught bank voles in deciduous woodland, young coniferous plantations and open habitats such as rank grass. The greater white-toothed shrew was absent from deciduous woods and plantations but did use open habitats with low level cover in addition to field margins. Numbers of both invasive species in field margins during summer were higher than in the previous spring. The indigenous wood mouse (Apodemus sylvaticus) and pygmy shrew (Sorex minutus), differed in degrees of negative response to invasive species. Wood mice with bank voles in hedgerows had reduced recruitment and lower peak abundance. This effect was less extreme where both invasive species were present. Wood mice numbers along field margins and open habitats were significantly depressed by the presence of the bank vole with no such effect in deciduous woodland or coniferous plantations. Summer recruitment in pygmy shrews was reduced in hedgerows with bank voles. Where greater white-toothed shrew was present, the pygmy shrew was entirely absent from field margins. Species replacement due to invasive small mammals is occurring in their major habitat i.e. field margins and open habitats where there is good ground cover. Pygmy shrew will probably disappear from these habitats throughout Ireland. Wood mice and possibly pygmy shrew may survive in deciduous woodland and conifer plantations. Mitigation of impacts of invasive species should include expansion of woodland in which native species can survive.

Richness of Lichen Species, Especially of Threatened Ones, Is Promoted by Management Methods Furthering Stand Continuity

Lichens are a key component of forest biodiversity. However, a comprehensive study analyzing lichen species richness in relation to several management types, extending over different regions and forest stages and including information on site conditions is missing for temperate European forests. In three German regions (Schwäbische Alb, Hainich-Dün, Schorfheide-Chorin), the so-called Biodiversity Exploratories, we studied lichen species richness in 631 forest plots of 400 m2 comprising different management types (unmanaged, selection cutting, deciduous and coniferous age-class forests resulting from clear cutting or shelterwood logging), various stand ages, and site conditions, typical for large parts of temperate Europe. We analyzed how lichen species richness responds to management and habitat variables (standing biomass, cover of deadwood, cover of rocks). We found strong regional differences with highest lichen species richness in the Schwäbische Alb, probably driven by regional differences in former air pollution, and in precipitation and habitat variables. Overall, unmanaged forests harbored 22% more threatened lichen species than managed age-class forests. In general, total, corticolous, and threatened lichen species richness did not differ among management types of deciduous forests. However, in the Schwäbische-Alb region, deciduous forests had 61% more lichen species than coniferous forests and they had 279% more threatened and 76% more corticolous lichen species. Old deciduous age classes were richer in corticolous lichen species than young ones, while old coniferous age-classes were poorer than young ones. Overall, our findings highlight the importance of stand continuity for conservation. To increase total and threatened lichen species richness we suggest (1) conserving unmanaged forests, (2) promoting silvicultural methods assuring stand continuity, (3) conserving old trees in managed forests, (4) promoting stands of native deciduous tree species instead of coniferous plantations, and (5) increasing the amount of deadwood in forests.