中国主要森林生态系统碳储量和碳收支评估

森林作为陆地生态系统中主要的植被类型在全球碳循环研究中有着十分重要的作用，而森林资源清样调查资料以其系统性、科学性、连续性等优点在森林生态系统碳循环研究中具有十分重要的地位。本研究以中国主要森林植被类型为研究对象，基于中国森林资源清样调查资料（FID），采用建立的生物气候生产力模型和反映林龄和蓄积量共同影响的生产力回归模型分别估计了中国油松林和主要造林树种的生产力;利用改进的材积源生物量法估算了中国主要森林植被类型的碳储量;并基于多元线性回归方法和因子分析法探讨了林业用地以及气候因子对中国森林植被碳储量的影响;同时，结合生物地球化学循环模型CENTURY模型评估了中国森林生态系统的碳收支。主要研究结果如下： 1建立了中国油松林生物气候生产力模型NPPa=［0.331n（V／A）+0.18］*3000（1-e-0.00096‘哪，根据油松林的森林资源清样调查资料和气候资料估算的中国油松林生产力平均为7.82Mg•ha-1•yr-1，其变化幅度为3.32-11.87Mg•ha-1•yr-1，其分布表现为南高北低的趋势。生产力较高的区域主要分布在东部和南部（四川、湖北、河南、辽宁等省），均大于7.7Mg•ha-1•yr-1;生产力较低的区域主要分布在北部和西部较为干旱的区域（内蒙古），NPP均低于5.5Mg•ha-1•yr-1：油松林集中分布区（陕西、山西）生产力处于中等水平，在5.5-7.7Mg•ha-1•yr-1之间。 2基于森林资源清样调查资料评估了中国五种主要造林树种（落叶松Larix，油松Pinusstabulaeformis，马尾松Pinusmassoniana，杉木Cunninghamialanceolata，杨树Populus）的生产力，分别为8.43、5.75、4.42、4.41、7.33Mg•ha-1•yr-1，低于世界平均生产力水平，主要原因可能是这五种造林树种大都处于未成熟阶段，表明中国造林树种在提高中国森林生态系统的固碳能力方面有很大的潜力。 3基于两次（第三次和第四次）森林资源清查资料和改进的材积源生物量法评估了中国森林的碳储量，分别为3.48和3.78PgC（1Pg＝1015g）。 基于多元线性回归模型探讨了林业用地变化对森林植被碳储量的影响。分析表明：在森林平均林龄减小的情况下，森林植被碳储量有增加的趋势;而森林碳储量随森林面积的增加而增加。当平均林龄增加10年，全国森林面积增加1*104ha时，全国森林植被的碳储量将增加54.51Tg（1Tg＝1012g），表明我国森林植被碳储量取决于自然和人为因素共同作用。 采用因子分析方法探讨了气候变化对森林植被碳储量的影响，分析表明：气温是森林植被碳储量的主要限制因子。当气温升高时，森林植被碳储量有降低的趋势;降水与森林植被碳储量呈正相关，随降水的增加森林植被碳储量增加。在年均温升高4℃，年降水量增加10％;年均温升高4℃，年降水量不变;年均温升高4℃，年降水量减少10％三种气候变化情景下，我国森林植被碳储量的增加量分别为：9.19Tg、6.67Tg和4.15Tg。 4基于生物地球化学循环模型模拟的中国森林生态系统的碳收支为0.17PgC，中国森林表现为一个巨大的碳汇。其中，西南地区森林碳收支占44％，华东及西北地区的森林碳收支总和不足14%。

The distribution and economic losses of alien species invasion to China

Invasive alien species have become one of the most serious environmental issues in the world. Data of taxon, origin, pathway, and environmental impacts of invasive alien microorganisms, invertebrates, amphibians and reptiles, fish, birds, mammals, herbs, trees, and, marine organisms in terrestrial, aquatic, and marine ecosystems of China were analyzed during 2001 and 2003, based on literature retrieval and field survey. There were 283 invasive alien species in China, and the number of species of invasive alien microorganisms, aquatic plants, terrestrial plants, aquatic invertebrates, terrestrial invertebrates, amphibians and reptiles, fish, and mammals were 19, 18, 170, 25, 33, 3, 10, and 5, respectively. The proportion of invasive alien species originated from America, Europe, Asia, Africa, and Oceania were 55.1, 21.7, 9.9, 8.1, and 0.6%, respectively. Methods for estimation of direct economic losses to agriculture, forestry, stockbreeding, fishery, road and water transportation, storage, water conservancy, environment and public facilities, and human health were established. Methods for estimation of indirect economic losses caused by invasive alien species to service functions of forest ecosystems, agricultural ecosystems, grassland ecosystems, and wetland ecosystems were also established. The total economic losses caused by invasive alien species to China were to the time of USD 14.45 billion, with direct and indirect economic losses accounting for 16.59% and 83.41% of total economic losses, respectively.

辽东山区次生林生态系统土壤动物多样性研究

土壤动物作为生态系统中重要的组成部分，在陆地生态系统中的物质循环、凋落物的分解以及土壤肥力保持中起着重要的调节作用。论文以辽东山区次生林生态系统中土壤动物为研究对象，旨在揭示土壤动物生态分布规律，为次生林生态系统的研究和可持续发展提供理论依据，为清原站积累数据。 本文综合野外调查、室内分析和统计，对不同林型、不同龄级落叶松人工林、不同干扰程度对土壤动物种类组成和动态的影响以及干扰对土壤线虫的群落结构的影响等问题进行分析研究， 研究结果表明：（1）共获取土壤动物3门、8纲、32目；线虫49属。优势类群为弹尾目与真螨目。（2）天然林比人工林具有稳定的生态环境，大中型土壤动物群落在生长季中波动范围小，凋落物本身理化性质和凋落物分解过程产生的不同微生物，导致了土壤动物类群的差异性；（3）27a落叶松人工林大中型土壤动物多样性与生物量高于9a落叶人工林与43a落叶松人工林，其原因可能是光照、温度、湿度，落叶松人工林的毒化作用等；（4）干扰改变了大中型土壤动物群落的种类组成，同时随着干扰度的增加，土壤动物的类群数与个体数减少。土壤动物多样性从小到大排序为：裸地土壤动物 < 人工林土壤动物< 次生林土壤动物；（5）干扰改变了线虫群落的种类组成，同时随着干扰度的增加，线虫的多样性减少，影响土壤线虫的主要原因有土壤养分，立地条件，地区不同光照所致等。

辽东山区次生林生态系统主要树种幼苗对光环境的响应

辽东山区森林是辽宁省重要的水源涵养基地与用材林资源，在维系区域内生态环境和林产品的可持续供应方面占据十分重要的战略位置。该区的天然林已基本绝迹，因此该区的森林生态恢复具有重要意义。 已有研究表明，影响辽东山区森林更新演替最主要的环境因素是光环境。核桃楸（Juglans mandshurica）、水曲柳（Fraxinus mandshurica）、黄菠萝（Phellodendron amurense）和红松(Pinus koraiensis)是阔叶红松林的优势树种；这些树种幼苗对光环境的适应性差异，在群落演替和森林生态恢复中发挥重要作用。 本论文采用人为控制遮光试验测定了核桃楸、水曲柳和黄菠萝幼苗对光环境的响应，同时，采用自然光环境试验和人为控制遮光试验相结合的手段测定了红松幼苗对光环境的适应性。人为控制遮光试验设置的光环境类似于自然中的典型林窗、林缘和林下的光环境；在人为控制遮光试验中，研究材料于2007年4月末栽植于4个不同光环境（全光、全光的60%、30%和15%，分别记为FI、II、LI和WI处理）下，在2007年7~9月测定了树种幼苗的光合生理、叶片特征、生长和冠层形态特征等方面的变化，结果表明： 1）不同光环境处理区内的光合有效辐射（PAR）具有显著差异，形成一定的光强梯度，而气温，相对湿度和土壤含水量差异并不显著。全光处理区内的日平均PAR为842.4μmol∙m-2∙s-1，最大PAR为1884.1μmol∙m-2∙s-1，显著高于其它处理区。 2）生长在高光强下4个树种幼苗的叶片有较高的光合能力（Amax），随生长光强的下降，Amax显著下降；光补偿点（LCP）和光饱和点（LSP）也表现出随着生长光强的下降而降低的趋势。核桃楸和水曲柳净光合速率Pn的日变化最大值约为16μmol∙m-2∙s-1，黄菠萝的约为13μmol∙m-2∙s-1，这与温带阔叶树种叶片的最大净光合速率Pn在10~15μmol∙m-2∙s-1范围内的结论相符；3个苗龄红松针叶的Pn日变化均呈单峰型，没有光合“午休”现象，峰值出现在11:00~13:00期间。 3）4个树种幼苗的比叶重（LMA）和单位叶面积鲜重（LFA）均随着光环境的降低而下降；三个阔叶树种幼苗的叶长L、叶宽W、叶周长C和单叶面积A均具有随着光强的降低而呈增大的趋势，表明叶片通过调节叶片的形态来适应多变的光环境。 4）不同光环境对阔叶树种幼苗的植株冠形和生长有显著影响，而红松幼苗植株冠形和生长的变化无明显的规律性。 综上，本研究得出以下结论：○1.通过可塑性分析和模糊隶属函数分析，核桃楸和黄菠萝较水曲柳能适应更宽的光强幅度；同时，核桃楸和黄菠萝较水曲柳的需光性更强，核桃楸和黄菠萝的需光性差异不大。○2.与3年、5年生红松相比，7年生红松对光强的适应幅度最小；同时，7年生红松的需光性强于3年和5年生红松。○3.本研究结果支持前人的观点：红松在幼年阶段能耐一定程度的遮光，在全光的20%~60%光条件下生长较好，随着年龄的增大，红松的需光性增加。

长白山典型森林生态系统土壤碳通量研究

森林生态系统是陆地最大的碳储存库，森林土壤呼吸是陆地生态系统土壤呼吸的重要组成部分，其动态变化将刘全球碳平衡产生深远的影响。精确测定土壤呼吸及其各组分的贡献，是目前全球变化研究中最基础和最迫切需要解决的问题。本文对长白山典型森林生态系统土壤碳通量及其过程机理进行了研究，结果表明：（1）阔叶红松林、红松云冷衫林、岳桦云冷杉林和岳桦林有不同的凋落节律；随海拔高度的上升，年凋落物量逐渐减少，分别为4.90、4.51、3.08和2.65thm-2；凋落物分解残留率与时间均呈指数关系，不同类型森林凋落物年分解常数的变化范围是25-47％之间。（2）阔叶红松林土壤总呼吸和断根土壤呼吸速率都存在明显的昼夜变化，为单峰型曲线，与土壤温度的昼夜变化趋势一致；不同森林类型土壤总呼吸和断根土壤呼吸的季节变化都比较明显，阔叶红松林、红松云冷杉林和岳桦云冷杉林变化趋势基本相似，都呈双峰型，岳桦林呈单峰型；土壤呼吸与土壤温度、大气温度之间都呈极显著（P＜0.01）指数相关关系，且与土壤温度的相关性要好于与大气温度的相关性；长白山四种类型森林土壤和根系呼吸的Q10值变化范围是1.8-2.9，根系呼吸的Q10值均大于土壤总呼吸和断根土壤呼吸的Q10值；土壤含水量对呼吸速率影响较为复杂，与土壤呼吸之间没有明显的相关关系；根系对土壤总呼吸贡献的季节变化与根系呼吸的季节变化相似，生长季内测定的阔叶红松林、红松云冷杉林、岳桦云冷杉林和岳桦杉林根系呼吸对土壤总呼吸贡献平均值分别为43.6％、44.1％、45.5％和44.4％。（3）长白山典型森林生态系统土壤碳的年释放量有随海拔高度上升而减小的趋势，且阔价卜林大于针叶林。阔叶红松林、红松云冷杉林、岳桦云冷杉林和岳桦林土壤碳的年释放量分别为7392.43、7181.83、6507.29和6841.09kghm-2a-1；根系的年碳释放量分别为3332.93、2965.68、2708.84和3015.48kghm-2a-1。

岷江上游人工针叶、阔叶林土壤可溶性有机物质特征及其对凋落物分解的响应

土壤可溶性有机物质（Dissolved organic matter，DOM）作为土壤有机质的活性组分，在陆地生态系统物质循环中扮演非常重要的角色。土壤DOM的主要成分可溶性有机碳（Dissolved organic carbon，DOC）和氮（Dissolved organic nitrogen，DON）参与C、N循环过程。为深入揭示全球C、N循环过程机制，在未开展DOC和DON的地区进行相关研究是有必要的。森林土壤（包括枯枝落叶层）DOC、DON动态及调控机理的研究是目前国际上森林生态系统C、N循环研究热点之一。本研究立足于暖温带岷江上游茂县地区人工林植被，对土壤DOC和DON的库容量，季节动态及其与其它养分之间的关系进行了系统研究，旨在了解DOC和DON在该区生态系统中的重要作用，并探讨作为DOM主要来源的叶凋落物对DOC和DON的动态影响，研究有助于更加详细地了解该区生态系统C和N循环过程。本论文主要研究结论如下： 1研究了岷江上游地区两大主要土壤类型（棕壤和褐土）不同植物群落下土壤的DOC和DON含量及特征，结果表明：DOC和DON在两种土壤类型中均有库容量存在，DOC在0-10cm和10-20cm土层的含量幅度分别111.96~159.95 mg kg-1和69.02~100.84 mg kg-1。DON在0-10cm和10-20cm土层的含量幅度分别11.88~23.08 mg kg-1和4.70~10.77 mg kg-1。游离氨基酸在0-10cm和10-20cm土层的含量幅度分别0.84~1.66 mg kg-1和0.39~0.73 mg kg-1。DOC、DON与土壤中的一些养分因子表现出了显著的相关关系，共同反映了土壤的状况和质量，在该区开展DOC和DON的系统研究是有必要的。 2 对油松与连香树林地土壤DOC、DON以及其它化学指标的季节动态进行了研究，结果表明：油松与连香树林地土壤DOC和DON的季节动态变化表现了类似的规律，DOC和DON的含量均以秋季最高。DOC和DON的季节动态变化主要受凋落物生物因素的影响，但其微生物活力的生物因素以及降雨、温度等非生物因素也是控制土壤DOC和DON含量的重要因素。土壤DON在土壤中的行为不同于矿质氮，其季节动态不同于NO3--N和NH4+-N的季节动态，在研究N循环过程中，应考虑DON的变化情况。 3 对油松与连香树林地分解层和表层土壤（0-10cm）氨基酸周转动态进行了研究，结果表明：油松林地和连香树林地均以分解层的氨基酸含量高于矿质表层土壤的含量。每个取样时期，油松林地内各层次的氨基酸含量高于连香树林地内相应层次的含量。两林地各层次无机氮含量均超过了氨基酸的含量，并且室内培养30天后无机N的含量仍然高于氨基酸的含量，所以可以认为该区立地条件下无论是在有机分解层还是矿质土层植物吸收利用的氮素仍是以无机N为主。 4 松林下松针凋落物易于累积，这与松针凋落物分解缓慢有关，从而导致松林内养分周转缓慢。通过用不同性质凋落物和灌丛地土壤构建微生态系统，比较油松、辐射松、连香树、灌丛虎榛子凋落物分解对C、N循环过程的影响，结果显示油松和辐射松针叶凋落物比连香树、虎榛子凋落物分解更慢，减缓了养分循环过程。然而将针叶凋落物与阔叶凋落物混合后，油松和辐射松针叶凋落物的分解加快，C、N元素的循环过程也加速。此结果表明在松林内维持具有高质量凋落物的灌丛植被或在松林内栽植一些阔叶树种如连香树对维持和增进松树人工林的土壤肥力有重大的作用。室内培养的结果还显示添加凋落物后土壤DOC和DON的含量显著增加，表明凋落物是土壤DOM的直接来源。然而不同物种凋落物处理下土壤DOC和DON的含量有所不同，并随时间发生改变。混合凋落物处理下土壤DOC和DON的含量均高于松针凋落物单独处理下土壤DOC和DON的含量。DON是一个主要的水溶性N库，随时间的变化趋势与无机N的变化趋势不同，在土壤N循环过程中起到了中间N库的作用。 As a labile fraction of soil organic matter, dissolved organic matter (DOM) plays a very important role in material cycling of terrestrial ecosystem. The turnover of DOM is now being considered as main components in nutrient cycling. DOM mainly includes dissolved organic carbon (DOC), -nitrogen (DON), -phosphorous (DOP) and –sulfur (DOS). Among these constituents, DOC and DON directly participate in C and N cycling. It is essential to study DOC and DON dynamics and their controlling factors in the areas where no related study has ever been carried out. Study about them can provide data supports on understanding the mechanism of the global C and N cycling. DOC and DON dynamics and their controlling factors have been focused on in the research of C and N cycling of forest ecosystems. Based on forest plantations of Maoxian, Minjiang River in warm temperate zone, soil DOC and DON pool size, their seasonal dynamics, and the correlation between DOC, DON and other nutrients were studied in order to understand the importance of DOC and DON in the study area. Soil DOC and DON dynamics induced by leaf litter decomposition were also studied. The study contributed to comprehensively understanding C and N cycling processes and providing baseline data for including DOC and DON into the indices system of evaluating nutrient conditions. The results were as follows: 1 Several different plant communities under brown soil and Cinnamon soil were chosen as sampling plots. The contents and features of soil DOC and DON were evaluated. The results showed that DOC and DON were present under the two soil types. DOC contents in the top soil (0-10 cm) and the subsoil (10-20 cm) respectively varied from 111.96 mg kg-1to 159.95 mg kg-1, and 69.02 mg kg-1 to 100.84 mg kg-1. DON contents in the top soil (0-10 cm) and the subsoil (10-20 cm) respectively varied from 11.88 mg kg-1to 23.08 mg kg-1, and 4.70 mg kg-1 to 10.77 mg kg-1. Free amino acid contents in the top soil (0-10 cm) and the subsoil (10-20 cm) respectively varied from 0.84 mg kg-1to 1.66 mg kg-1, and 0.39 mg kg-1 to 0.73 mg kg-1. Significant correlations were found between DOC, DON and some nutrient indices, which together reflected soil condition and quality. It was hence essential to study DOC and DON in the study area. 2 Seasonal dynamics of DOC, DON, inorganic N, microbial biomass C and N were studied under Pinus tabulaeformis and Cercidiphyllum japonicum plantation. The results indicated that seasonal dynamics of soil DOC and DON under the two plantations performed similar change pattern, with the highest values in autumn. The seasonal dynamics of soil DOC and DON were mainly influenced by the litterfall. However, biotic factors such as soil microbial activities and abiotic factors such as precipitation and temperature also controlled the dynamics of soil DOC and DON. The seasonal dynamic of DON was different from that of NO3--N and NH4+-N, which showed that the behavioral differences between DON and inorganic nitrogen. And hence, it was proposed to include DON into soil N cycling in the study area. 3 Amino acid dynamics in Oa and topsoil (0-10 cm) under P. tabulaeformis and C. japonicum plantation were studied. The results showed that amino acid content in Oa was significantly higher than that in mineral soil. At each sampling time, significantly higher amino acid contents were found in P. tabulaeformis plantation than in C. japonicum plantation. The content of inorganic nitrogen was much higher than the content of amino acid in each sampling layer at each sampling time. After a 30-days laboratory incubation the content of amino acid was still lower than the content of inorganic nitrogen. The results implicated that the form of N absorbed by plants in these study sites were mainly inorganic nitrogen. 4 Usually needle litter is more resistant to decomposition, which leads to needle litter accumulation in pure coniferous stands and slows down the rate of nutrient circulation. By constructing microcosms with local shrubland soil and containing the four single-species (P. tabulaeformis, P. radiata, C. japonicum, Ostryopsis davidiana) litters, the decomposition rates and related C and N dynamics of needle litters and broadleaved litters during the early stage were compared. The results showed that the decomposition rates of pine needles were lower than those of broadleaved litters, which descended C and N cycling processes. However, the presence of C. japonicum or O. davidiana litter into pine needles increased the decomposition rates of pine needles and also dramatically promoted C and N cycling processes. It should be appropriate for plantation managers to consider C. japonicum as an ameliorative species or remain O. davidiana in pine plantations to improve soil conditions and help maintain soil fertility. The laboratory incubation still showed that DOC and DON contents in all litter-amended treatments were significantly higher than no litter-amended treatment, which proved that litter could be a direct source of DOM in soils. Different species litters induced different soil DOC and DON contents, which correspondingly changed over time. DOC and DON contents in mixed litter treatments were higher than those in pine needle litter treatments. As a major soluble N pool, DON developed a different changing pattern over time compared with inorganic N and played a role of interim N pool in soil N cycling.

青藏高原东缘高山林线乔木种群生态特征研究

青藏高原东部分布着世界最高的林线，该区域也是由欧亚北温带物种形成的林线的南界。在大面积野外踏勘的基础上，选择青藏高原东部具有典型高山林线分布的三个地点（滇西北白马雪山、川西北鹧鸪山及岷江源地区）作为研究区，从种群的结构、生存特征、分布格局及分形特征等方面对青藏高原东缘高山林线乔木种群生态学特征进行了研究，并在此基础上探讨了人类活动对林线种群生态特征及林线格局的影响。结果表明，林线区乔木树种多以单种群形式存在，林线区群落结构简单，乔木层多为单一树种组成，其生长型较之郁闭林发生了急剧的变化：树木高度急剧下降，而发展多茎多分枝的生长型。生长型的转变是高山林线乔木对恶劣自然条件的形态适应。 研究发现，在青藏高原东缘，阴坡林线乔木主要是冷杉（Abies spp.），阳坡主要由圆柏（Sabina spp.）组成，少数地方还有云杉（Picea spp.）。阴坡乔木种群结构多表现为增长型，幼苗和幼树在种群中占较大比重，种群潜在自然更新能力较强，但幼龄个体死亡率非常高，存活曲线多接近Deevey-Ⅲ型；阳坡乔木种群幼苗个体数极少，幼树相对增加。野外调查表明，人为活动较频繁的阳坡林线区幼苗数量极少甚至缺失，而受人为活动干扰较小的样地中幼苗和幼树数量明显增多，从一个侧面说明放牧等人类活动可能对林线种群的更新带来较大影响，而对卡卡沟围栏内外的样地分析也进一步证明了这一结果。 所研究林线乔木种群各龄级的空间格局在不同尺度上表现为聚集、随机和均匀分布，以聚集分布为主；各龄级在不同尺度上表现出显著的相关性，幼苗通常与另外两个龄级的关联性较密切。各龄级间显著的相关性表明不同龄级个体在空间交错分布，有利于对各种资源的充分利用，对种群的生存和发展非常有利，反映了高山生态系统恶劣生境中种群的一种适应对策。 林线乔木种群各龄级分布格局的计盒维数有差别，林线种群的计盒维数总是小于郁闭林种群的计盒维数。另外，郁闭林各龄级计盒维数通常也高于林线各龄级，表明不同海拔或者不同群落类型中的乔木树种具有不同的水平空间占据能力。林线区种群分布格局的计盒维数都很低，占据现实水平空间的程度较低，具有相对较高的生态间隙维，其潜在占据空间的能力较高，群落还可提供给种群的最大空间限度较大，但实际上由于受群落中种内、种间的竞争及林线区恶劣的生态环境条件的限制，其潜在空间占据能力可能难以表现出来。 青藏高原东缘高海拔地带以季节性游牧为主要的资源利用和生产方式，阳坡森林郁闭度低于阴坡，灌丛数量和种类较阴坡少，融雪早且积雪时间短，所以阳坡包括高山林线区成为当地牧民游牧路线的必经之地。牲畜的践踏、啃食使得幼龄乔木树种个体数量大大减少，严重阻碍了林线乔木种群的自然更新，同时种群占据空间的能力也明显降低。因此可以认为，在青藏高原东部地区，山地游牧等人为干扰叠加于恶劣的自然条件，阳坡林线的自然更新潜力受到抑制，其生存状态较之阴坡林线显著恶化，并可使阳坡林线高度逐渐降低。高山林线区森林一旦破坏在短时间内很难有效更新和恢复，因此，对于处于恶劣高山生境中的乔木种群应加强保护，同时适度控制人为干扰强度和幅度以减少其直接和间接破坏，防止阳坡林线退化并促进高山生态系统的自然恢复。 Eastern Qinghai-Tibetan Plateau has the highest timberline of the world. On the basis of field surveys and literature reviews, three typical alpine timberlines were chosen for in-depth studies, i.e., Baima Snow Mountain in northwest Yunnan, Zhegu Mountain and the waterhead area of Minjiang River in west Sichuan. Using the methodologis of population ecology, we analyzed the population structure, survival characteristics, spatial point patterns and fractal dimensions of the timberline tree populations and discussed the impacts of grazing on the structure and spatial pattern of alpine timberline. Compared with closed forests, the community structure of timberline is simpler, usually with one or two species constituting the tree layer. Differences also exist in the growth forms: the trees were significantly shorter with more stems and branches, reflecting morphological adaptation of trees to the severe conditions at timberline. In the eastern Qinghai-Tibetan Plateau, Abies spp. often formed alpine timberline in the north-facing slope while Sabina spp. and sometimes Picea spp. in the south- facing slope. The population structures of north-facing slope showed an increasing trend, with numerous seedlings and saplings. However, the survival curves tend to follow Deevy-III because of high dead ratio of young individuals. There are only few seedlings in the south-facing slope with heavy grazing, demonstrating that human disturbance may prevent regeneration at alpine timberline, which was confirmed by comparisons between fenced enclosures and control plots in the Kaka Valley. Depending on the spatial scales on consideration, the individuals of different age-classes showed clumping, random or even distribution, but mostly with clumping distribution. At all scales, individuals in different age-classes were all significantly correlated with each other while the seedlings were usually more correlated to two other age classes. This high degree of correlation among different age classes indicates that individuals of different age classes are spatially interlocked with each other, which helps sufficient utilization of various resources and is conducive to the survival and development of population. It is another adaptation strategy for trees at the severe environment. The spatial patterns of different age classes had different box dimension. In general, the box dimensions of total individuals and each age class at timberline are always smaller than that of closed forests, suggesting that space occupation capacity is not the same for populations at different altitude or in different communities. Populations on both the south- and the north-facing slopes had a very low box dimensions (far away from the max., 2), however, the lower the box dimension, the bigger the potential space provided by community. In fact, because of inner- and inter- competition as well as the severe conditions at timberline, this kind of potential ability can hardly be realized. Mountain pastoralism is the major type of as well as the only most effective way of resource uses in the high elevation regions of the eastern Qinghai-Tibetan Plateau. Due to lower canopy cover, less bushes and short snow-cover time, south-facing slopes became the favorite pastures. Damages from livestock through tramping, browsing and others have greatly reduced the number of young individuals. As a result, the potential of timberline trees to regenerate and their ability to occupy more space are greatly inhitibted. We conclude that human disturbances (mountain pastoralism) as well as harsh environmental conditions co-worked to inhibit the regeneration of tree populations in the south-facing slope and made south slopes more difficult than the north-facing slopes for trees to survive and develop, resulting a gradual retreat of timberline in the north-facing slopes. Forests at alpine timberline are susceptible to disturbance and difficult to regenerate and restore once damaged and controlling human disturbances is important for protecting the forest ecosystems at the timberline area.

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.

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.

Effects of nitrogen fertilization on soil respiration in temperate grassland in Inner Mongolia, China

Nitrogen addition to soil can play a vital role in influencing the losses of soil carbon by respiration in N-deficient terrestrial ecosystems. The aim of this study was to clarify the effects of different levels of nitrogen fertilization (HN, 200 kg N ha(-1) year(-1); MN, 100 kg N ha(-1) year(-1); LN, 50 kg N ha(-1) year(-1)) on soil respiration compared with non-fertilization (CK, 0 kg N ha(-1) year(-1)), from July 2007 to September 2008, in temperate grassland in Inner Mongolia, China. Results showed that N fertilization did not change the seasonal patterns of soil respiration, which were mainly controlled by soil heat-water conditions. However, N fertilization could change the relationships between soil respiration and soil temperature, and water regimes. Soil respiration dependence on soil moisture was increased by N fertilization, and the soil temperature sensitivity was similar in the treatments of HN, LN, and CK treatments (Q (10) varied within 1.70-1.74) but was slightly reduced in MN treatment (Q (10) = 1.63). N fertilization increased soil CO2 emission in the order MN > HN > LN compared with the CK treatment. The positive effects reached a significant level for HN and MN (P < 0.05) and reached a marginally significant level for LN (P = 0.059 < 0.1) based on the cumulative soil respiration during the 2007 growing season after fertilization (July-September 2007). Furthermore, the differences between the three fertilization treatments and CK reached the very significant level of 0.01 on the basis of the data during the first entire year after fertilization (July 2007-June 2008). The annual total soil respiration was 53, 57, and 24% higher than in the CK plots (465 g m(-2) year(-1)). However, the positive effects did not reach the significant level for any treatment in the 2008 growing season after the second year fertilization (July-September 2008, P > 0.05). The pairwise differences between the three N-level treatments were not significant in either year (P > 0.05).

Seasonal patterns of gross primary production and ecosystem respiration in an alpine meadow ecosystem on the Qinghai-Tibetan Plateau

We measured the net ecosystem CO2 exchange (NEE) in an alpine meadow ecosystem (latitude 37degrees29'-45'N, longitude 101degrees12'-23'E, 3250 m above sea level) on the Qinghai-Tibetan Plateau throughout 2002 by the eddy covariance method to examine the carbon dynamics and budget on this unique plateau. Diurnal changes in gross primary production (GPP) and ecosystem respiration (R-e) showed that an afternoon increase of NEE was highly associated with an increase of R-e. Seasonal changes in GPP corresponded well to changes in the leaf area index and daily photosynthetic photon flux density. The ratio of GPP/R-e was high and reached about 2.0 during the peak growing season, which indicates that mainly autotrophic respiration controlled the carbon dynamics of the ecosystem. Seasonal changes in mean GPP and R-e showed compensatory behavior as reported for temperate and Mediterranean ecosystems, but those of GPP(max) and R-emax were poorly synchronized. The alpine ecosystem exhibited lower GPP (575 g C m(-2) y(-1)) than, but net ecosystem production (78.5 g C m(-2) y(-1)) similar to, that of subalpine forest ecosystems. The results suggest that the alpine meadow behaved as a CO2 sink during the 1-year measurement period but apparently sequestered a rather small amount of C in comparison with similar alpine ecosystems.

Wybiórczość siedliskowa dzięcioła średniego Dendrocopos medius w zróżnicowanych ekosystemach leśnych

Wydział Biologii

Inter-annual variability of precipitation constrains the production response of boreal Pinus sylvestris to nitrogen fertilization

© 2015 Published by Elsevier B.V.Tree growth resources and the efficiency of resource-use for biomass production determine the productivity of forest ecosystems. In nutrient-limited forests, nitrogen (N)-fertilization increases foliage [N], which may increase photosynthetic rates, leaf area index (L), and thus light interception (IC). The product of such changes is a higher gross primary production and higher net primary production (NPP). However, fertilization may also alter carbohydrate partitioning from below- to aboveground, increasing aboveground NPP (ANPP). We analyzed effects of long-term N-fertilization on NPP, and that of long-term carbon storing organs (NPPS) in a Pinus sylvestris forest on sandy soil, a wide-ranging forest type in the boreal region. We based our analyses on a combination of destructive harvesting, consecutive mensuration, and optical measurements of canopy openness. After eight-year fertilization with a total of 70gNm^-2, ANPP was 27±7% higher in the fertilized (F) relative to the reference (R) stand, but although L increased relative to its pre-fertilization values, IC was not greater than in R. On the seventh year after the treatment initiation, the increase of ANPP was matched by the decrease of belowground NPP (78 vs. 92gCm^-2yr^-1; ~17% of NPP) and, given the similarity of IC, suggests that the main effect of N-fertilization was changed carbon partitioning rather than increased canopy photosynthesis. Annual NPPS increased linearly with growing season temperature (T) in both treatments, with an upward shift of 70.2gCm^-2yr^-1 by fertilization, which also caused greater amount of unexplained variation (r²=0.53 in R, 0.21 in F). Residuals of the NPPS-T relationship of F were related to growing season precipitation (P, r²=0.48), indicating that T constrains productivity at this site regardless of fertility, while P is important in determining productivity where N-limitation is alleviated. We estimated that, in a growing season average T (11.5±1.0°C; 33-year-mean), NPPS response to N-fertilization will be nullified with P 31mm less than the mean (325±85mm), and would double with P 109mm greater than the mean. These results suggest that inter-annual variation in climate, particularly in P, may help explaining the reported large variability in growth responses to fertilization of pine stands on sandy soils. Furthermore, forest management of long-rotation systems, such as those of boreal and northern temperate forests, must consider the efficiency of fertilization in terms of wood production in the context of changes in climate predicted for the region.

Problems of dynamic in mediterranean forests

The mediterranean forest ecosystems constitute a complex unit which is marked off the Northern and middle European ones by its climate, ecology and management.The ecosystems are related to a climate with estival droughtlasting from 1 to 6 months and the peculiar species which constitute them are generally not worth much.The anthropic pressure exerts especially by grazing and moreover they have been stricken by dramatic fires for many decades. Their large variety related to the bioclimatic and edaphic heterogeneity of the region can explain why the data concerning their functioning and dynamics are still fragmentary. Besides, their ecological and pedological characteristics make uneasy the use of schemes and patterns designed for middle european forests.

The pace of Holocene vegetation change - testing for synchronous developments

Mid to high latitude forest ecosystems have undergone several major compositional changes during the Holocene. The temporal and spatial patterns of these vegetation changes hold potential information to their causes and triggers. Here we test the hypothesis that the timing of vegetation change was synchronous on a sub-continental scale, which implies a common trigger or a step-like change in climate parameters. Pollen diagrams from selected European regions were statistically divided into assemblage zones and the temporal pattern of the zone boundaries analysed. The results show that the temporal pattern of vegetation change was significantly different from random. Times of change cluster around8.2, 4.8, 3.7, and 1.2 ka, while times of higher than average stability were found around 2.1 and 5.1 ka.Compositional changes linked to the expansion of Corylus avellana and Alnus glutinosa centre around 10.6 and 9.5 ka, respectively. A climatic trigger initiating these changes may have occurred 0.5 to 1 ka earlier, respectively. The synchronous expansion of C. avellana and A. glutinosa exemplify that dispersal is not necessarily followed by population expansion. The partly synchronous, partly random expansion of A. glutinosa in adjacent European regions exemplifies that sudden synchronous population expansions are not species specific traits but vary regionally.