Altitudinal differences in the leaf fitness of juvenile and mature alpine spruce trees (Picea crassifolia)

In many plant species, leaf morphology varies with altitude, an effect that has been attributed to temperature. It remains uncertain whether such a trend applies equally to juvenile and mature trees across altitudinal gradients in semi-arid mountain regions. We examined altitude-related differences in a variety of needle characteristics of juvenile (2-m tall) and mature (5-m tall) alpine spruce (Picea crassifolia Kom.) trees growing at altitudes between 2501 and 3450 m in the Qilian Mountains of northwest China. We found that stable carbon isotope composition (delta C-13), area- and mass-based leaf nitrogen concentration (N-a, N-m), number of stomata per gram of nitrogen (St/N), number of stomata per unit leaf mass (St/LM), projected leaf area per 100 needles (LA) and leaf mass per unit area (LMA) varied nonlinearly with altitude for both juvenile and mature trees, with a relationship reversal point at about 3 100 m. Stomatal density (SD) of juvenile trees remained unchanged with altitude, whereas SD and stomatal number per unit length (SNL) of mature spruce initially increased with altitude, but subsequently decreased. Although several measured indices were generally found to be higher in mature trees than in juvenile trees, N-m, leaf carbon concentration (C.), leaf water concentration. (LWC), St/N, LA and St/LM showed inconsistent differences between trees of different ages along the altitudinal gradient. In both juvenile and mature trees, VC correlated significantly with LMA, N-m, N-a, SNL, St/LM and St/N. Stomatal density, LWC and LA were only significantly correlated with delta C-13 in mature trees. These findings suggest that there are distinct ecophysiological differences between the needles of juvenile and mature trees that determine their response to changes in altitude in semi-arid mountainous regions. Variations in the fitness of forests of different ages may have important implications for modeling forest responses to changes in environmental conditions, such as predicted future temperature increases in high attitude areas associated with climate change.

Fertilisation residues alter leaf scleromorphy in an evergreen savannah shrub (Maprounea brasiliensis, Euphorbiaceae)

In the present study, we examined how residues of nitrogen (N), phosphorus (P) and calcium (Ca) fertilisers affect leaf anatomical traits in Maprounea brasiliensis (Euphorbiaceae), a typical and dominant cerrado (Brazilian savannah) species adapted to dystrophic soils. We predicted that fertiliser residues would alter qualitative and quantitative aspects of M. brasiliensis leaves and would decrease their scleromorphy. Leaves were sampled from plants that were growing in soils previously fertilised with N, P and Ca and in plants that were growing in soils without fertiliser residues. We measured the thickness of the cuticle, the epidermis of adaxial and abaxial surfaces, thickness of palisade parenchyma and spongy parenchyma, total thickness of the leaf, total area of the midrib and leaf mass per area (LMA). We found that plants under fertiliser residues produced fewer scleromorphic leaves with low LMA, thinner cuticle and epidermis and thicker palisade and spongy parenchyma. They also showed a decrease in the size and area occupied by the leaf midvein. However, plants under fertiliser residues produced similar leaf thickness as did the plants in the control group. Our results showed that residual effects of fertilisation changed structural patterns of a typical species of cerrado. Thus, further studies about fertilisation effects on leaf traits are needed because larger areas of the central cerrado are being occupied for agricultural production. © 2013 CSIRO.

(Table 3) Leaf area and leaf nitrogen for deciduous, evergreen, forb and graminoid species at Barrow, Svalbard and Zackenberg

Arctic vegetation is characterized by high spatial variability in plant functional type (PFT) composition and gross primary productivity (P). Despite this variability, the two main drivers of P in sub-Arctic tundra are leaf area index (LT) and total foliar nitrogen (NT). LT and NT have been shown to be tightly coupled across PFTs in sub-Arctic tundra vegetation, which simplifies up-scaling by allowing quantification of the main drivers of P from remotely sensed LT. Our objective was to test the LT-NT relationship across multiple Arctic latitudes and to assess LT as a predictor of P for the pan-Arctic. Including PFT-specific parameters in models of LT-NT coupling provided only incremental improvements in model fit, but significant improvements were gained from including site-specific parameters. The degree of curvature in the LT-NT relationship, controlled by a fitted canopy nitrogen extinction co-efficient, was negatively related to average levels of diffuse radiation at a site. This is consistent with theoretical predictions of more uniform vertical canopy N distributions under diffuse light conditions. Higher latitude sites had higher average leaf N content by mass (NM), and we show for the first time that LT-NT coupling is achieved across latitudes via canopy-scale trade-offs between NM and leaf mass per unit leaf area (LM). Site-specific parameters provided small but significant improvements in models of P based on LT and moss cover. Our results suggest that differences in LT-NT coupling between sites could be used to improve pan-Arctic models of P and we provide unique evidence that prevailing radiation conditions can significantly affect N allocation over regional scales.

The relevance of seed size in modulating leaf physiology and early plant performance in two tree species

he size of seeds and the microsite of seed dispersal may affect the early establishment of seedlings through different physiological processes. Here, we examined the effects of seed size and light availability on seedling growth and survival, and whether such effects were mediated by water use efficiency. Acorns of Quercus petraea and the more drought-tolerant Quercus pyrenaica were sowed within and around a tree canopy gap in a sub-Mediterranean forest stand. We monitored seedling emergence and measured predawn leaf water potential (Ψpd), leaf nitrogen per unit area (Na), leaf mass per area, leaf carbon isotope composition (δ13C) and plant growth at the end of the first summer. Survival was measured on the next year. Path analysis revealed a consistent pattern in both species of higher δ13C as Ψpd decreased and higher δ13C as seedlings emerged later in the season, indicating an increase in 13C as the growing season is shorter and drier. There was a direct positive effect of seed size on δ13C in Q. petraea that was absent in Q. pyrenaica. Leaf δ13C had no effect on growth but the probability of surviving until the second year was higher for those seedlings of Q. pyrenaica that had lower δ13C on the first year. In conclusion, leaf δ13C is affected by seed size, seedling emergence time and the availability of light and water, however, leaf δ13C is irrelevant for first year growth, which is directly dependent on the amount of seed reserves.

Importance of water source in controlling leaf leaching losses in a dwarf red mangrove (Rhizophora mangle L.) wetland

The southern Everglades mangrove ecotone is characterized by extensive dwarf Rhizophora mangle L. shrub forests with a seasonally variable water source (Everglades – NE Florida Bay) and residence times ranging from short to long. We conducted a leaf leaching experiment to understand the influence that water source and its corresponding water quality have on (1) the early decay of R. mangle leaves and (2) the early exchange of total organic carbon (TOC) and total phosphorus (TP) between leaves and the water column. Newly senesced leaves collected from lower Taylor River (FL) were incubated in bottles containing water from one of three sources (Everglades, ambient mangrove, and Florida Bay) that spanned a range of salinity from 0 to 32‰, [TOC] from 710 to 1400 μM, and [TP] from 0.17 to 0.33 μM. We poisoned half the bottles in order to quantify abiotic processes (i.e., leaching) and assumed that non-poisoned bottles represented both biotic (i.e., microbial) and abiotic processes. We sacrificed bottles after 1,2, 5, 10, and 21 days of incubation and quantified changes in leaf mass and changes in water column [TOC] and [TP]. We saw 10–20% loss of leaf mass after 24 h—independent of water treatment—that leveled off by Day 21. After 3 weeks, non-poisoned leaves lost more mass than poisoned leaves, and there was only an effect of salinity on mass loss in poisoned incubations—with greatest leaching-associated losses in Everglades freshwater. Normalized concentrations of TOC in the water column increased by more than two orders of magnitude after 21 days with no effect of salinity and no difference between poisoned and non-poisoned treatments. However, normalized [TP] was lower in non-poisoned incubations as a result of immobilization by epiphytic microbes. This immobilization was greatest in Everglades freshwater and reflects the high P demand in this ecosystem. Immobilization of leached P in mangrove water and Florida Bay water was delayed by several days and may indicate an initial microbial limitation by labile C during the dry season.

INVERTEBRATE CONTRIBUTION TO LEAF BREAKDOWN IN PYNN’S BROOK, NL.

Leaf bags of fine and coarse mesh were placed at two locations, one with an open tree canopy, the other with a closed tree canopy, in Pynn’s Brook on June 30th 2015. Bags were collected after 2, 30, 37 and 44 days. After collection, invertebrates were counted and leaf material remaining was determined to measure leaf breakdown rate. There was no significant difference in leaf mass remaining (R) between the two sites. Comparisons between mesh types found a difference in leaf breakdown at two collection days. The difference at 2 days was small (2.7%) and may not be biologically meaningful. At 37 days, the difference was larger (8.41%) and may be related to a larger proportion of shredder taxa, seen in coarse mesh bags, or higher absolute numbers of invertebrates. The invertebrate community was dominated by Diptera spp. across all collection days and mesh types, but after 37 days, communities in coarse mesh bags had a higher proportion of shredder orders than did fine mesh bags.

Forage mass and morphological composition of Marandu palisade grass pasture under rest periods.

2016

Seasonal changes in pasture quality and diet selection and their relationship with liveweight gain of steers grazing tropical grass and grass-legume pastures in northern Australia.

The variation in liveweight gain in grazing beef cattle as influenced by pasture type, season and year effects has important economic implications for mixed crop-livestock systems and the ability to better predict such variation would benefit beef producers by providing a guide for decision making. To identify key determinants of liveweight change of Brahman-cross steers grazing subtropical pastures, measurements of pasture quality and quantity, and diet quality in parallel with liveweight were made over two consecutive grazing seasons (48 and 46 weeks, respectively), on mixed Clitoria ternatea/grass, Stylosanthes seabrana/grass and grass swards (grass being a mixture of Bothriochloa insculpta cv. Bisset, Dichanthium sericeum and Panicum maximum var. trichoglume cv. Petrie). Steers grazing the legume-based pastures had the highest growth rate and gained between 64 and 142 kg more than those grazing the grass pastures in under 12 months. Using an exponential model, green leaf mass, green leaf %, adjusted green leaf % (adjusted for inedible woody legume stems), faecal near infrared reflectance spectroscopy predictions of diet crude protein and diet dry matter digestibility, accounted for 77, 74, 80, 63 and 60%, respectively, of the variation in daily weight gain when data were pooled across pasture types and grazing seasons. The standard error of the regressions indicated that 95% prediction intervals were large (+/- 0.42-0.64 kg/head.day) suggesting that derived regression relationships have limited practical application for accurately estimating growth rate. In this study, animal factors, especially compensatory growth effects, appeared to have a major influence on growth rate in relation to pasture and diet attributes. It was concluded that predictions of growth rate based only on pasture or diet attributes are unlikely to be accurate or reliable. Nevertheless, key pasture attributes such as green leaf mass and green leaf% provide a robust indication of what proportion of the potential growth rate of the grazing animals can be achieved.

Eriophyid mites on spotted gums: population and histological damage studies of an emerging pest

A suite of co-occurring eriophyid mite species are significant pests in subtropical Australia, causing severe discolouration, blistering, necrosis and leaf loss to one of the region's most important hardwood species, Corymbia citriodora subsp. variegata (F. Muell.) K. D. Hill & L. A. S. Johnson (Myrtaceae). In this study, we examined mite population dynamics and leaf damage over a 1-year period in a commercial plantation of C. citriodora subsp. variegata. Our aims were to link the incidence and severity of mite damage, and mite numbers, to leaf physical traits (moisture content and specific leaf weight (SLW)); to identify any seasonal changes in leaf surface occupancy (upper vs. lower lamina); and host tree canopy strata (upper, mid or lower canopy). We compared population trends with site rainfall, temperature and humidity. We also examined physical and anatomical changes in leaf tissue in response to mite infestation to characterize the plants' physiological reaction to feeding, and how this might affect photosynthesis. Our main findings included positive correlations with leaf moisture content and mite numbers and with mite numbers and damage severity. Wet and dry leaf mass and SLW were greater for damaged tissue than undamaged tissue. Mites were distributed equally throughout the canopy and on both leaf surfaces. No relationships with climatic factors were found. Damage symptoms occurred equally and were exactly mirrored on both leaf surfaces. Mite infestation increased the overall epidermal thickness and the number and size of epidermal cells and was also associated with a rapid loss of chloroplasts from mesophyll cells beneath damage sites. The integrity of the stomatal complex was severely compromised in damaged tissues. These histological changes suggest that damage by these mites will negatively impact the photosynthetic efficiency of susceptible plantation species.

Eriophyid mites on spotted gums: population and histological damage studies of an emerging pest

A suite of co-occurring eriophyid mite species are significant pests in subtropical Australia, causing severe discolouration, blistering, necrosis and leaf loss to one of the region's most important hardwood species, Corymbia citriodora subsp. variegata (F. Muell.) K. D. Hill & L. A. S. Johnson (Myrtaceae). In this study, we examined mite population dynamics and leaf damage over a 1-year period in a commercial plantation of C. citriodora subsp. variegata. Our aims were to link the incidence and severity of mite damage, and mite numbers, to leaf physical traits (moisture content and specific leaf weight (SLW)); to identify any seasonal changes in leaf surface occupancy (upper vs. lower lamina); and host tree canopy strata (upper, mid or lower canopy). We compared population trends with site rainfall, temperature and humidity. We also examined physical and anatomical changes in leaf tissue in response to mite infestation to characterize the plants' physiological reaction to feeding, and how this might affect photosynthesis. Our main findings included positive correlations with leaf moisture content and mite numbers and with mite numbers and damage severity. Wet and dry leaf mass and SLW were greater for damaged tissue than undamaged tissue. Mites were distributed equally throughout the canopy and on both leaf surfaces. No relationships with climatic factors were found. Damage symptoms occurred equally and were exactly mirrored on both leaf surfaces. Mite infestation increased the overall epidermal thickness and the number and size of epidermal cells and was also associated with a rapid loss of chloroplasts from mesophyll cells beneath damage sites. The integrity of the stomatal complex was severely compromised in damaged tissues. These histological changes suggest that damage by these mites will negatively impact the photosynthetic efficiency of susceptible plantation species.

Photosynthesis of ground vegetation in boreal Scots pine forests

Research on carbon uptake in boreal forests has mainly focused on mature trees, even though ground vegetation species are effective assimilators and can substantially contribute to the CO2 uptake of forests. Here, I examine the photosynthesis of the most common species of ground vegetation in a series of differently aged Scots pine stands, and at two clear-cut sites with substantial differences in fertility. In general, the biomass of evergreen species was highest at poor sites and below canopies, whereas grasses and herbs predominated at fertile sites and open areas. Unlike mosses, the measured vascular species showed clear annual cycles in their photosynthetic activity, which increased earlier and decreased later in evergreen vascular species than in deciduous species. However, intraspecific variation and self-shading create differences in the overall level of photosynthesis. Light, temperature history, soil moisture and recent possible frosts could explain the changes in photosynthesis of low shrubs and partially also some changes in deciduous species. Light and the occurrence of rain events explained most of the variation in the photosynthesis of mosses. The photosynthetic production of ground vegetation was first upscaled, using species-specific and mass-based photosynthetic activities and average biomass of the site, and then integrated over the growing season, using changes in environmental factors. Leaf mass-based photosynthesis was highest in deciduous species, resulting in notably higher photosynthetic production at fertile sites than at poor clear-cut sites. The photosynthetic production decreased with stand age, because flora changed towards evergreen species, and light levels diminished below the canopy. In addition, the leaf mass-based photosynthetic activity of some low shrubs declined with the age of the surrounding trees. Different measuring methods led to different momentary rate of photosynthesis. Therefore, the choice of measuring method needs special attention.

Caracterização das estratégias ecofisiológicas de samambaias em resposta à inundação na restinga de Maricá, Rio de Janeiro, Brasil

As matas inundáveis e brejos presentes nas restingas desencadeiam uma série de processos que influenciam as características físico-químicas e biológicas do solo, levando as plantas a apresentarem mecanismos de aclimatação ou adaptação ao estresse da inundação, como alterações morfológicas e fisiológicas de forma a minimizar os efeitos da falta de oxigênio. Dentre as espécies vegetais de samambaias ocorrentes em ambientes inundáveis nas restingas, se destacam três espécies: Acrostichum danaeifolium Langsd. & Fisch., Blechnum serrulatum Rich. e Thelypteris interrupta (Willd.) K.Iwats. O objetivo deste trabalho é caracterizar os aspectos ecofisiológicos que os esporófitos dessas samambaias apresentam para sobreviver em ambientes de inundação na restinga de Maricá, estado do Rio de Janeiro. Neste sentido, foi determinada a caracterização física e química dos sítios de ocorrências destas samambaias, as variações foliares entre elas, espessura, densidade, massa por unidade de folha, teor de clorofilas e atributos quantitativos das células epidérmicas, além da quantificação e determinação à distribuição dos carboidratos. Para as variáveis dos vegetais foram feitas coletas na estação chuvosa e seca e para variáveis do solo na estação seca. Os sítios analisados se mostraram extremamente ácidos, de baixa fertilidade e com toxidez por macro e micro nutrientes, indicando que as samambaias apresentam tolerância a estes fatores. Na época chuvosa (inundação), as samambaias apresentaram queda na densidade foliar, acompanhada de um aumento de massa por unidade de folha. Esta habilidade de conseguir ganhar massa seca por área classifica todas as samambaias analisadas como tolerantes à inundação. Os altos valores de carboidratos solúveis nas folhas indicam aumento da degradação do amido foliar e o menor teor de carboidrato solúvel encontrado nos caules explicita a redução na respiração das raízes destas plantas sob anoxia/ hipoxia, para evitar a oxidação e o incremento do estoque de amido de reserva, elucidando estratégia de tolerância à inundação. A menor disponibilidade de água na estação seca afeta diretamente os atributos foliares diminuindo o índice estomático, a suculência e a massa por unidade de folha, no qual reflete na queda das concentrações de clorofilas. Os menores valores nas concentrações de clorofila têm influencia direta na presença de amidos foliar que são estocado e, alterando toda a dinâmica dos carboidratos nestas espécies. A análise do sítio onde cresce Acrostichum danaeifolium indica níveis críticos de Na no solo e provavelmente, a produção de mucilagem no caule e no pecíolo é uma estratégia de tolerância ao ambiente salino e inundado. O elevado índice de cobertura de Blechnum serrulatum em ambientes inundados indica que esta espécie possui adaptações a solos hidromórficos, entre elas, grande capacidade de estocagem de amido no caule. A maior sinuosidade das células epidérmicas em T. interrupta permite uma alta suculência mantendo o status hidrológico da folha em ambas as estações. Os resultados apresentados, além de agregar informações sobre a biologia das samambaias nos neotrópicos, irão contribuir para a compreensão da dinâmica de ocupação de espécies herbáceas em ambientes alagáveis nas restingas brasileiras

大尺度环境梯度上羊草种群适应性研究

　　由于全球气候变化，干旱化问题已经成为制约植物生存、影响农作物产量的主要环境因子，因此有关植物在大尺度环境梯度上对环境因子变化的适应性研究已经成为生态学研究的热点。目前环境变化对植被生产力的影响已经有了广泛研究，但是关于植物在形态解剖和渗透调节等生理特征上对大尺环境梯度变化的适应机制研究报道却很少。本研究以北纬43°16′-44°36′；东经125°17′-115°43′范围内的羊草草地为研究对象，探讨羊草主要形态解剖特征、生理渗透调节特征等的变化规律及其与环境因子的关系，以期揭示大尺度环境梯度上羊草种群对环境变化的响应规律和适应策略。本研究的主要结果如下： 在大尺度环境梯度下，羊草种群的气孔密度和气孔指数表现出非常相似的变化趋势，均为由东向西呈先降后升的变化趋势，且与降水等因子的相关关系为V型二次曲线。这是因为气孔的蒸腾作用是植物散失水分的主要途径，同时蒸腾作用产生的蒸腾拉力是植物根部吸收水分的主要动力，因此这种V型曲线正是它在野外对如何调节体内失水和吸水的一种权衡的结果。由于羊草叶片的营养生长和器官建成主要在7月份，这也导致了该月的平均降水对气孔密度和气孔指数有很重要的影响作用。 在该梯度下，羊草叶片厚度和LMA（Leaf mass per unit area, 单位面积叶重）等形态性状指标、叶片解剖学特征等表现出有规律的变化趋势。具体表现为从东向西随着气候由湿润到干旱的变化，叶片厚度、LMA呈增加趋势；同样维管束、木质部及导管直径和叶片厚度等变化趋势相似，从东向西逐渐增加,它们均与七月份温度显著相关。这说明外界环境变化对羊草的形态性状和解剖特征等产生了显著的影响，而且羊草也会通过改变形态解剖特征等来适应大尺度环境梯度变化。 在本研究中，羊草叶片脯氨酸和可溶糖份含量等生理指标也随着环境梯度的变化呈现出明显的规律变化，主要表现为由东至西随降水量的减少而逐渐增加；叶片钠离子和钾离子含量虽然有一定变化，但是它们与气候因子变化并不一致，而分别与土壤里钠离子和钾离子含量呈显著的相关关系。这说明自东向西随着干旱程度的增加，脯氨酸和可溶糖份含量对羊草适应环境变化起着主要的渗透调节作用。 自然条件下，羊草主要有两种生态型，根据叶片颜色的差异分别为灰绿型(GG)和黄绿型(YG)。它们在分布上也表现出很大的差异，其中灰绿型羊草分布范围更广，且更耐盐碱。我们分别选取查干花和绍根两个样点镶嵌生长的两种生态型羊草，对它们的叶片形态解剖特征和渗透调节特征进行比较。结果显示无论是在查干花还是绍根地区，在同一生境条件下，黄绿型羊草叶片厚度、LMA、及维管束直径、木质部直径和导管直径等均比灰绿型高，而气孔密度和气孔指数比灰绿型低，在形态上表现出明显的旱生化特征。而灰绿型羊草叶片则有较高的脯氨酸含量、可溶糖份含量及钾离子含量，较低的钠离子含量，表现出较强的渗透调节能力、更强的选择性排钠离子和吸收钾离子的能力。为此我们推断在相同生境下两种生态型羊草在应对干旱和盐碱胁迫时在形态和生理上采取不同的适应策略，而且这两种策略是互相补充，这就解释了两种生态型羊草能够镶嵌生长的现象。

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.

增温对川西北高寒草甸植物群落结构及几种主要植物生长和生理的影响

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 ℃，并预测在本世纪将上升1.4-5.8 ℃。气候变暖对陆地植物和生态系统影响深远，并已成为全球变化研究的重要议题。高海拔、高纬度地带的生态系统对气候变化最敏感。而在高原和高山极端环境影响下所形成的高寒草甸生态系统极其脆弱，对由于温室效应引起的全球气候变化极其敏感，对这些变化的响应更具有超前性。 本研究以川西北高寒草甸植物群落及几种主要物种为研究对象，采用国际山地综合研究中心（ITEX）普遍所采用的增温方法-----开顶式生长室（OTC）模拟气候变暖来研究增温对高寒草甸植物群落结构、物质分配及其主要物种生长和生理的影响，以探讨高寒草甸植物响应与适应气候变暖的生物学和生态学机制。主要研究结论如下： 1、OTC的增温效果 由于地温、地表温度和气温的平均值在OTC内分别高出对照样地0.28℃、0.46℃和1.4℃，这说明本研究所采用的开顶式生长室（OTC）起到了增温的作用；同时，由于温室内与温室外接受的降水量相同，温室内由于热量条件的改善，土壤蒸发和植被的蒸腾作用增强，直接导致了OTC内土壤表层相对湿度的减少。 2、群落结构对增温的响应 由于增温时间较短，增温内外样地的物种组成并未发生改变；但增温后一定程度上改变了植物群落的小气候环境，从而导致物种间的竞争关系被破坏，种间竞争关系的破坏引起群落优势种组成发生相应的改变，在对照样地，鹅绒委陵菜、甘青老鹳草、遏蓝菜和蚤缀是占绝对优势的物种，而在OTC内，小米草、尼泊尔酸模、垂穗披碱草、发草和羊茅的重要性显著增加。 禾草和杂草由于对增温的生物学特性及其资源利用响应的不同，加之增温造成土壤含水量下降等环境因子的改变。与对照样地相比较，OTC内禾草的盖度及生物量都显著增加，而杂草的盖度和生物量则显著下降。 3、植物生长期对增温的响应 OTC内立枯和调落物的生物量在生长季末（10月份）都要小于对照样地的立枯和调落物生物量，而OTC内的地上鲜体生物量在10月份却略高于对照样地。这说明OTC内植物的衰老或死亡得以延缓，而植物的生长期得以延长。 4、群落生物量及分配对增温的响应 OTC内的地上鲜体生物量(10月份除外)和地下0-30cm的根系生物量与对照样地相比较，都出现了不同程度的减少；土壤根系的分配格局也发生了明显的改变，其中，OTC内0-10cm土层的生物量分配比例增加，而20-30cm土层生物量分配比例的减少。 5、群落碳、氮对增温的响应 增温后，OTC内植物群落地上活体和地下活根的碳浓度不同程度的高于对照样地，植物群落的碳库在OTC内也略高于对照样地；而OTC内植物群落地上活体和地下活根的氮浓度不同程度的低于对照样地，其植物群落的氮库与对照样地相比也略有下降。 6、几种主要植物的生长及物质分配对增温的响应 垂穗披碱草在增温后株高、比叶面积和地上生物量均显著地增加；尼泊尔酸模在增温后比叶面积和单株平均生物量积累显著地增加，而各组分中，增温处理使叶的生物量显著增加，而根的生物量却显著下降；鹅绒委陵菜在增温后株高、比叶面积和单株平均生物量积累显著地减少，而各组分中，增温处理使叶和茎的生物量显著减少，根的生物量却显著地增加。 尼泊尔酸模的LMR、RMR、R/S、根部碳含量、碳和氮在叶片与根部的分配比例在增温后显著地增加，而SMR、根部氮含量、碳和氮在茎部的分配比例在增温后却显著地降低；鹅绒委陵菜的RMR、R/S、碳和氮在根部的分配比例在增温后显著地增加，而SMR、LMR、碳在叶片的分配比例在增温后却显著地降低 7、几种主要植物的光合生理过程对增温的响应 增温使垂穗披碱草和尼泊尔酸模叶片中的叶绿素a、叶绿素b、总叶绿素含量显著增加；而鹅绒委陵菜叶片的叶绿素a、叶绿素b、总叶绿素含量在增温后显著减少，类胡萝卜素含量在增温后却显著增加。 增温对3种植物的气体交换产生了显著影响。其中，垂穗披碱草和尼泊尔酸模叶片的光响应曲线在增温后明显高于对照处理，A、E、gs、Pmax、、Rday、AQY和LSP显著增加，而LCP则显著降低；鹅绒委陵菜的光响应曲线在增温后则明显的低于对照处理，A、E、gs、Pmax、、Rday、AQY和LSP显著减少，而LCP则显著增加。 增温后垂穗披碱草和尼泊尔酸模叶片的Fv/Fm、Yield和qP显著增加；而鹅绒委陵菜叶片的Fv/Fm、Yield和qP则显著减少，qN却显著地增加。 8、几种主要植物的抗氧化酶系统对增温的响应 增温使垂穗披碱草和尼泊尔酸模体内抗氧化酶活性和非酶促作用有所提高，植物膜脂过氧化作用降低；鹅绒委陵菜叶片中酶促反应和非酶促反应在增温后也显著提高，但可能由于增温后的土壤干旱超过了鹅绒委陵菜叶的抗氧化保护能力，抗氧化酶活性及非酶促反应（脯氨酸、类胡萝卜素）的提高不足以完全清除干旱诱导形成的过量活性氧，因此叶片的膜脂过氧化程度仍然显著提高。 Enrichment of atmospheric greenhouse gases resulted from human activities such as fossil fuel burning and deforestation has increased global mean temperature by 0.6 ℃ in the 20th century and is predicted to increase in this century by 1.4-5.8 ℃. The global warming will have profound, long-term impacts on terrestrial plants and ecosystems. The ecoologcial consequences arising from global warming have also become the very important issuses of global change research. The terrestrial habitats of high-elevation and high-latitude ecosystems are regarded as the most sensitive to changing climate. The alpine meadow ecosystme, which resulted from the composite effects of mountain extreme climatic factors in Tibetan Plateau, is thus thought to be especially vulnerable and sensitive to global warming. In this paper, the response of plant community and several main species in the alpine meadow of Northewst Sichuan to experimemtal warming was studied by using open-top chambers (OTC). The aim of the this study was to research the warming effects on plant community structure, substance allocation, growth and physiological processes of several mian species, and to explore the biological and ecological mechanism of how the alpine meadow plants acclimate and adapt to future global warming. The results were as follows: 1. Warming effects of OTC The mean soil temperature, soil surface temperature and air temperature in OTC manipulation increased by 0.28℃、0.46℃ and 1.4℃ compared to the control during the growing season. This suggested that the OTC used in our study had increased temperature there. Meanwhile, the OTC manipulation slightly altered thermal conditions, but the same amount of precipitation was supplied to both the OTC manipulation and the control, so higher soil evaporation and plant transpiration in OTC manipulation directly lead to the decrease of soil surface water content. 2. The reponse of community structure to experimental warming The species richness was not changed by the short-term effect of OTC manipulation. However, experimental warming changed the microenvironment of plant community, therefore competitive balances among species were shift, leading to changes in species dominance. In the present study, the dominant plant species in the control plots were some forbs including Potentilla anserine, Geranium pylzowianum, Thlaspi arvense and Arenaria serpyllifolia, however, the importance value of some gramineous grasses including Elymus nutans, Deschampsia caespitosa, Festuca ovina, and some forbs including Euphrasia tatarica and Rumex acetosa significantly increased in OTC. The different biology characteristics and resource utilizations between gramineous grasses and forbs, and enhanced temperature caused change in some environment factors such as soil water content. As a result, the coverage and biomass of gramineous grasses significantly increased in OTC compared to the control, however, the coverage and biomass of forbs singnifciantly decreased in OTC compared to the control. 3. The reponse of plant growing season to experimental warming Both the standing dead and fallen litter biomass in OTC were lower than those in the control in October, and the biomass of aboveground live-vegetation in OTC was higher than that of the control. The results indicated that the senescence of plants was postponed, and the growing season was prolonged in our research. 4. The reponse of community biomass accumulation and its allocation to experimental warming Experimental warming caused the decrease of aboveground live biomass and belowground root biomass except for the aboveground live biomass in October. Experimental warming also had pronounced effects on the pattern of root biomass allocation. In the present study, the root biomass in 0-10cm soil layer increased in OTC manipulation compared to the control, however, the root biomass in the 20-30cm soil layer decreased in OTC manipulation compared to the control. 5. The reponse of community C and N content to experimental warming The C concentration and stock in aboveground live and belowground root both increased in OTC manipulation compared to the control. However, the N concentration and stock in aboveground live and belowground root both decreased in OTC manipulation compared to the control. 6. The reponse of gowth and biomass, C and N alloction of several species to experimental warming Experimental warming significantly increased the height, SLA (specific leaf area) and aboveground biomass of Elymus nutans in OTC manipulation compared to the control. The SLA and total biomass of Rumex acetosa also significantly increased in OTC manipulation compared to control, among the different components of Rumex acetosa, leaf biomass significantly increased, but root biomass significantly decreased in OTC manipulation compared to the control. However, the height, SLA and total biomass of Potentilla anserina significantly decreased in OTC manipulation compared to the control, among the different component of Potentilla anserina, leaf and stem biomass significantly decreased, but root biomass significantly increased in OTC manipulation compared to the control. The LMR (leaf mass ratio), RMR (root mass ratio), R/S (shoot/root biomass ration) and root C concentration of Rumex acetosa significantly increased in OTC manipulation compared to outside control, also, Rumex acetosa allocated relatively more C and N content to leaf and root in response to experimental warming, however, the SMR (stem mass ration) and root N concentration of Rumex acetosa significantly decreased in OTC manipulation compared to outside control, also, Rumex acetosa allocated relatively less C and N content to stem in response to experimental warming. The RMR and R/S of Potentilla anserina significantly increased in OTC manipulation compared to outside control, also, Potentilla anserina allocated relatively more C and N content to root in response to experimental warming, however, the SMR and LMR of Potentilla anserina significantly decreased in OTC manipulation compared to outside control, also, Potentilla anserina allocated relatively less C and N content to leaf in response to experimental warming. 7. The reponse of physiological processes of several species to experimental warming Experimental warming significantly increased chlorophyll a, chlorophyll b and total chlorophyll of Elymus nutans and Rumex acetosa in OTC manipulation compared to outside control. However, chlorophyll a, chlorophyll b, total chlorophyll and carotenoid of Potentilla anserina in OTC manipulation significantly decreased compared to outside control. Experimental warming had pronounced effects on gas exchange of Elymus nutans, Rumex acetosa and Potentilla anserine. In the present study, warming markedly increased the light response curves of Elymus nutans and Rumex acetosa in OTC manipulation compared to outside control, and also singnificantly increased A (net photosynthesis rate), E (transpiration rate), gs (stomatal conductance), Pmax (maximum net photosynthetic rate), Rday (dark respiration rate), AQY (apparent quantum yield) and LSP (light saturation point), but LCP (photosynthetic light compensation) of Elymus nutans and Rumex acetosa in OTC manipulation singnificantly decreased compared to outside control. However, warming markedly decreased the light response curves of Potentilla anserina in OTC manipulation compared to outside control, and also singnificantly decreased A, E, gs, Pmax, Rday, AQY and LSP, but LCP of Potentilla anserina in OTC manipulation singnificantly increased compared to outside control. Experimental warming singnificantly increased the chlorophyll fluorescence kinetics parameters such as Fv/Fm, Yield and qP of Elymus nutans and Rumex acetosa and qN of Potentilla anserina in OTC manipulation, but Fv/Fm, Yield and qP of Potentilla anserina in OTC manipulation singnificantly decreased. 8. The reponse of antioxidative systems of several species to experimental warming Experimental warming tended to increase the activities of antioxidative enzymes and stimulate the role of non-enzymes of Elymus nutans and Rumex acetosa. As a result, MDA content of Elymus nutans and Rumex acetosa decreased. The activities of antioxidative enzymes and non-enzymes of Potentilla anserina also significantly increased in OTC manipulation, but more O2- was produced because of lower soil water content, and the O2- accumulation exceeded the defense ability of antioxidative systems and non-enzymes fuctions. As a result, MDA content of Potentilla anserine still increased in OTC manipulation compared to outside control.