Vertical leaf nitrogen distribution in relation to nitrogen status in grassland plants

Vertical gradients of leaf nitrogen (N) per unit leaf area (NLA) are viewed as plastic responses that optimize N utilization with respect to carbon assimilation. However, it has been shown that plant species, sowing density and N availability affect the steepness of the NLA gradient relative to the photon flux density (PFD) gradient. This paper tests the hypothesis that such variation is related to the N status of the plant. The N status was analysed using the concept of the critical N concentration (Ncrit) in which shoot N per unit dry mass (NSM) decreases with shoot mass, and a negative deviation of actual NSM from Ncrit indicates N shortage in the plant. The hypothesis was tested with contrasting grassland species Medicago sativa, Dactylis glomerata and Taraxacum officinale by varying PFD and N availability, plant density and hierarchical positions of individuals within stands. Combinations of all treatments showed a general negative correlation between the N allocation coefficient (i.e. the slope of the NLA-PFD relationship) and NSM for all three species. Thus, NLA, relative to PFD, gradients became steeper with increasing shoot mass and increasing N shortage in the plant. These data are consistent with the view that internal N availability is an important factor in modifying the NLA gradient.     

Leaf dynamics,self-shading and carbon gain in seedlings of a tropical pioneer tree

We examined leaf dynamics and leaf age gradients of photosynthetic capacity and nitrogen concentration in seedlings of the tropical pioneer tree, Heliocarpus appendiculatus, grown in a factorial design under controlled conditions with two levels each of nutrients, ambient light (light levels incident above the canopy), and self-shading (the gradient of light levels from upper to lower leaves on the shoot). Correlations among these parameters were examined in order to determine the influence of self-shading, and the regulation of standing leaf numbers, on leaf longevity and its association with leaf photosynthetic capacity. Leaf longevity and the number of leaves on the main shoot were both reduced in high light, while in the low light environment, they were reduced in the steeper self-shading gradient. In high nutrients, leaf longevity was reduced whereas leaf number increased. Leaf initiation rates were higher in the high nutrient treatment but were not influenced by either light treatment. Maximum-light saturated photosynthetic rate, on an area basis, was greater in the high light and nutrient treatments, while the decline in photosynthetic capacity in realtion to leaf position on the shoot was more rapid in high light and in low nutrients. Leaf longevity was negatively correlated among treatments with initial photosynthetic capacity. The leaf position at which photosynthetic capacity was predicted to reach zero was positively correlated with the number of leaves on the shoot, supporting the hypothesis that leaf numbers are regulated by patterns of self-shading. The negative association of longevity and initial photosynthetic capacity apparently arises from different associations among gradients of photosynthetic capacity, leaf numbers and leaf initiation rates in relation to light and nutrient availability. The simultaneous consideration of age and position of leaves illuminates the role of self-shading as an important factor influencing leaf senescence and canopy structure and dynamics.     

麻栎和闽楠幼苗叶功能性状及生物量对光照和施肥的响应

光照和养分条件是影响植物生长的重要环境因子,不同生活型植物对环境异质性的响应机制不同。以落叶阔叶树种麻栎和常绿阔叶树种闽楠幼苗为研究对象,设置2个光照梯度（全光照和45%全光照）和4个施肥梯度（不施肥、氮磷供应比为5、15和45）共8种处理,研究光照和施肥及其交互作用对麻栎和闽楠生物量和叶形态、生理及化学性状的影响,并探讨了叶功能性状和生物量的关系。结果表明：（1）光照、施肥及其交互作用对光合气体交换参数（除水分利用效率外）、叶绿素荧光参数、叶形态指标（除比叶面积外）、单位质量叶氮含量和根冠比影响显著（P<0.05）。此外,光照和施肥对地上生物量和总生物量影响显著（P<0.05）。（2）全光照显著增加了麻栎和闽楠单株总叶面积和地上、地下生物量及总生物量（P<0.05）,而遮荫降低了非光化学猝灭系数、光合氮利用率和根冠比,增加了单位质量叶氮含量。（3）在全光照处理中,施肥显著增加了麻栎和闽楠水分利用效率（P<0.05）;在遮荫处理中,氮磷供应比45显著增加了麻栎和闽楠净光合速率和水分利用效率（P<0.05）。（4）麻栎和闽楠在全光照中倾向于资源获取策略,在遮荫中偏向于资源保守策略。在光照和施肥处理中,麻栎和闽楠单株总叶面积与地上生物量均显著正相关（P<0.05）。总之,单株总叶面积是预测麻栎和闽楠幼苗地上生物量变化的稳定指标,施肥有助于增加低光环境下麻栎和闽楠幼苗的生态适应能力。     

延河流域植物叶性状间关系及其在不同植被带的表达

以延河流域不同植被带的地带性植物群落为研究对象,对群落优势种和主要伴生种的6种叶片性状进行测定,分析这些性状及其关系随环境梯度的变化,以了解该区域植物对环境变化的适应策略.结果表明: 植物比叶面积(SLA)与叶组织密度(LTD)、叶片单位面积氮和磷含量均呈显著负相关,与单位质量叶片磷含量呈显著正相关;各性状间的尺度关系和生存对策在不同植被带不同,典型草原带和森林草原带植物LTD SLA的尺度依赖关系比森林带植物的强,而森林带植物叶片单位〖JP2〗面积N、P含量与SLA、LTD间的尺度关系较草原带更明显,植物对环境的适应策略发生了位移.在干旱贫瘠的草原带和森林草原带,植物以防御和抗胁迫策略为主,而在环境条件相对湿润、富养的森林带,植物以快速生长和资源优化配置策略为主.     

The effects of light and nitrogen on photosynthesis,leaf characteristics,and dry matter allocation in the chaparral shrub,Diplacus aurantiacus

Summary Plants of Diplacus aurantiacus, a successional shrub common in California chaparral, were grown under controlled conditions in which either quantum flux density or nitrogen availability was varied. Photosynthesis and leaf nitrogen content were determined on a leaf area and a leaf weight basis, and whole plant growth was monitored.There was a direct relationship between photosynthesis and leaf nitrogen content on both area and weight bases. Reduced light intensity of the growth environment resulted in reductions in light-saturated photosynthesis and nitrogen content on an area basis, but not on a weight basis. With reduced nitrogen availability, photosynthesis and leaf nitrogen content per unit leaf weight decreased.Resource use efficiency increased as the resource became more limiting. The results are consistent with a model of plant growth in which net carbon gain of the leaf is maximized. Abbreviations. For brevity, the following set of abbreviations is used in presenting and discussing the results. P/area and N/area are, respectively, photosynthesis and leaf nitrogen content per unit leaf area. P/wt and N/wt are the same quantities per unit leaf dry weight. SLW (specific leaf weight) is dry weight per unit leaf area. RGR (relative growth rate) is the relative rate of increase in shoot dry matter per day     

Leaf position,light levels,and nitrogen allocation in five species of rain forest pioneer trees

We used path analysis to ask whether leaf position or leaf light level was a better predictor of within-plant variation in leaf nitrogen concentration in five species of rain forest pioneer trees (Cecropia obtusifolia, Ficus insipida, Heliocarpus appendiculatus, Piper auritum, and Urera caracasana) from the Los Tuxtlas Biological Station, Veracruz, Mexico. Three hundred seventy-five leaves on 28 plants of the five species were analyzed for leaf nitrogen concentration, leaf mass per area, and leaf light interception at different positions (= nodes) along a shoot. Mean values of leaf nitrogen concentration ranged from 0.697 to 0.993 g/m² in the five species, and varied by as much as 2.24 g/m² among leaves on individual plants. Leaf position on the shoot explained significantly more of the within-plant variation in leaf nitrogen concentration than did leaf light level in four of the five species: Cecropia obtusifolia, Heliocarpus appendiculatus, Piper auritum (branch leaves only), and Urera caracasana. However, individual species differed considerably in the patterns of nitrogen allocation and leaf mass per area among leaves on a shoot. These results suggest that leaf nitrogen deployment in these plants is, in part, developmentally constrained and related to the predictability of canopy light distribution associated with plant growth form.     

车桑子幼苗生物量分配与叶性状对氮磷浓度的响应差异

调整叶性状和生物量分配格局是植物适应环境变化的主要途径, 研究车桑子(Dodonaea viscosa)幼苗生物量分配与叶性状对氮磷浓度的响应对认识车桑子在氮磷浓度变化下的适应策略具有重要意义。该研究通过砂培法, 测定不同氮浓度(3、5、15、30 mmol·L^-1)与不同磷浓度(0.25、0.5、1、2 mmol·L^-1)下车桑子幼苗的生长、生物量分配、叶性状的响应特征及其相互关系。结果表明: 高浓度氮(30 mmol·L^-1)促进了车桑子幼苗生长、叶片氮含量和生物量积累, 其余氮添加条件(3、5、15 mmol·L^-1)下车桑子幼苗各性状无显著差异, 但相比高氮水平, 其生物量积累和叶片氮含量显著降低, 根冠比和氮利用效率显著增加。随着磷添加浓度的增加, 车桑子幼苗生物量显著增加, 低磷条件(0.25、0.5 mmol·L^-1)限制了车桑子幼苗生长和生物量积累, 其根冠比和磷利用效率均没有发生显著变化, 但比叶面积和叶/茎生物量比例显著增加, 叶干物质含量显著降低。氮处理下, 叶片氮含量与根冠比显著负相关; 磷处理下, 叶片氮含量与比叶面积显著正相关。同时, 氮处理下, 车桑子幼苗株高、基径、总生物量等生长性状均与根冠比显著负相关, 与叶片氮含量显著正相关, 表明根冠比和叶片氮含量的调整在车桑子适应氮限制中发挥重要作用; 而磷处理下, 株高、基径、总生物量与比叶面积显著负相关, 与叶干物质含量显著正相关, 表明叶片结构性状的调整在车桑子适应低磷环境中具有重要意义。该研究表明, 车桑子幼苗生物量分配和叶性状及性状间的权衡策略对氮、磷的响应具有明显差异性, 在今后的研究中, 应关注氮和磷对植物性状影响的差异性。     

Different responses of biomass allocation and leaf traits of Dodonaea viscosa to concentrations of nitrogen and phosphorus

调整叶性状和生物量分配格局是植物适应环境变化的主要途径, 研究车桑子(Dodonaea viscosa)幼苗生物量分配与叶性状对氮磷浓度的响应对认识车桑子在氮磷浓度变化下的适应策略具有重要意义。该研究通过砂培法, 测定不同氮浓度(3、5、15、30 mmol·L^-1)与不同磷浓度(0.25、0.5、1、2 mmol·L^-1)下车桑子幼苗的生长、生物量分配、叶性状的响应特征及其相互关系。结果表明: 高浓度氮(30 mmol·L^-1)促进了车桑子幼苗生长、叶片氮含量和生物量积累, 其余氮添加条件(3、5、15 mmol·L^-1)下车桑子幼苗各性状无显著差异, 但相比高氮水平, 其生物量积累和叶片氮含量显著降低, 根冠比和氮利用效率显著增加。随着磷添加浓度的增加, 车桑子幼苗生物量显著增加, 低磷条件(0.25、0.5 mmol·L^-1)限制了车桑子幼苗生长和生物量积累, 其根冠比和磷利用效率均没有发生显著变化, 但比叶面积和叶/茎生物量比例显著增加, 叶干物质含量显著降低。氮处理下, 叶片氮含量与根冠比显著负相关; 磷处理下, 叶片氮含量与比叶面积显著正相关。同时, 氮处理下, 车桑子幼苗株高、基径、总生物量等生长性状均与根冠比显著负相关, 与叶片氮含量显著正相关, 表明根冠比和叶片氮含量的调整在车桑子适应氮限制中发挥重要作用; 而磷处理下, 株高、基径、总生物量与比叶面积显著负相关, 与叶干物质含量显著正相关, 表明叶片结构性状的调整在车桑子适应低磷环境中具有重要意义。该研究表明, 车桑子幼苗生物量分配和叶性状及性状间的权衡策略对氮、磷的响应具有明显差异性, 在今后的研究中, 应关注氮和磷对植物性状影响的差异性。     

Effects of leaf age, nitrogen nutrition and photon flux density on the organization of the photosynthetic apparatus in leaves of a vine (Ipomoea tricolor Cav.) grown horizontally to avoid mutual shading of leaves

Effects of leaf age, nitrogen nutrition and photon flux density (PFD) on the organization of the photosynthetic apparatus in leaves were investigated in a vine, Ipomoea tricolor Cav., which was grown horizontally so as to avoid mutual shading of leaves. The plants were grown hydroponically at two nitrate levels under two growth light treatments. For one group of the plants, leaves were exposed to full sunlight. For another group, respective leaves were artificially shaded in a manner that simulated changes in the light gradient with the development of an erect herbaceous canopy: old leaves were placed under progressively shadier conditions with growth of the plants (canopy-type shading). In all the treatments, chlorophyll (Chl) content gradually decreased with leaf age. Photosystem I (PSI) per Chl was constant, independent of leaf age, nitrogen nutrition and/or PFD. Photosystem II (PSII) and cytochrome / per Chl, and Chl a/b ratio were independent of leaf age and/or nitrogen nutrition but decreased with the decrease in growth PFD. Ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39, RuBPCase) per Chl steeply decreased with decrease in PFD. When leaves grown at the same PFD were compared, RuBPCase/Chl was lower in the plants grown under lower nitrogen availability and also decreased with leaf age in the plants grown without shading. These decreases were attributed to the curvilinear relationship between RuBPCase and Chl in leaves grown at full sunlight, that was independent of nitrogen availability and leaf age. From these results, it is concluded that the composition of the photosynthetic apparatus is independent of leaf age but changes depending on the light environment and total amount of photosynthetic components of the leaf.Abbreviations Chl chlorophyll - cyt f cytochrome f - PFD photon flux density - RuBPCase ribulose-1,5-bisphosphate carboxylase The author thanks Drs. K. Sonoike, Y. Kashino, K. Okada, H. Hatanaka, Y. Suzuki and A. Aoyama for technical advise. The author also thanks Drs. I. Terashima, A. Makino (Tohoku University, Sendai, Japan), Dr. J.R. Evans (Research School of Biological Sciences, Australian National University, Canberra) and Prof. A. Watanabe for valuable suggestions.     

敦煌阳关湿地芦苇叶性状对土壤水分的响应

为了了解干旱区湿地不同水分梯度下芦苇叶性状的构建模式及对不同水分环境的适应策略差异性,以敦煌阳关渥洼池湿地植物芦苇(Phragmites australis)为研究对象,分析不同水分梯度下芦苇叶性状对土壤水分的响应。结果表明:(1)低水分梯度下的叶厚度(LT)和叶片磷含量(LPC)显著高于中、高水分梯度(P0.05),高水分梯度下的叶碳含量(LCC)也显著高于中、低水分梯度(P0.05)。(2)芦苇叶性状之间的关系也因水分的变化而有所不同。就整体而言,叶片碳含量与叶干物质含量(LDMC)极显著正相关(P0.01);叶厚度与叶片磷含量极显著正相关(P0.01),比叶面积(SLA)与叶氮含量(LNC)极显著正相关(P0.01)、与叶碳氮比(C/N)极显著负相关(P0.01)。(3)在水分作为限制因素的条件下,叶片碳含量与比叶面积对水分的响应最为突出。土壤含水量与叶厚度、叶碳含量和叶片磷含量均显著负相关(P0.05)。芦苇在低水分环境下采取高收入低投入的积极型生存策略,高水分下则采取低获取高消耗的保守型生存策略,说明了芦苇在适应异质生境的自我调节机制。     

Effects of light and nutrient availability on the growth,allocation, carbon/nitrogen balance,phenolic chemistry,and resistance to herbivory of two freshwater macrophytes

Phenotypic responses of Potamogeton amplifolius and Nuphar advena to different light (7% and 35% of surface irradiance) and nutrient environments were assessed with field manipulation experiments. Higher light and nutrient availability enhanced the growth of P. amplifolius by 154% and 255%, respectively. Additionally, biomass was allocated differently depending on the resource: high light availability resulted in a higher root/shoot ratio, whereas high nutrient availability resulted in a lower root/shoot ratio. Low light availability and high nutrient availability increased the nitrogen content of leaf tissue by 53% and 40% respectively, resulting in a 37% and 31% decrease in the C/N ratio. Root nitrogen content was also increased by low light and high nutrient availability, by 50% (P=0.0807) and 77% respectively, resulting in a 20% and 40% decrease in root C/N ratio. Leaf phenolics were significantly increased 72% by high light and 31% by high nutrient availability, but root phenolic concentrations were not altered significantly. None of these changes in tissue constituents resulted in altered palatability to crayfish. N. advena was killed by the same high nutrient treatment that stimulated growth in P. amplifolius, preventing assessment of phenotypic responses to nutrient availability. However, high light availability increased overall growth by 24%, but this was mainly due to increased growth of the rhizome (increased 100%), resulting in a higher root/shoot ratio. High light tended to increase the production of floating leaves (P=0.09) and significantly decreased the production of submersed leaves. High light availability decreased the nitrogen content by 15% and 25% and increased the phenolic concentration by 88% and 255% in floating and submersed leaves, respectively. These differences in leaf traits did not result in detectable differences in damage by herbivores.     

A Model Allocating Growth Among Leaf Proteins, Shoot Structure, and Root Biomass to Produce Balanced Activity

A model is developed that considers the allocation of carbonand nitrogen substrates to a protein compartment in the shoots,shoot structural components, and root biomass. Inclusion ofa shoot-protein compartment allows variation in shoot-specificactivity to be modelled as a function of leaf nitrogen concentration.Allocation to the biomass compartments is controlled by twopartitioning variables that are defined by explicitly usingthe balanced activity hypothesis. The model produces balancedactivity where the shoot-specific activity, as well as rootand shoot biomass, vary in response to the above-ground (lightand CO₂) and below-ground (nitrogen) environments. The predictedpatterns of both root: shoot ratio and leaf nitrogen concentrationin response to environmental resource availability are qualitativelyconsistent with general trends observed in plants. Biomass allocation, plant growth, modelling, leaf nitrogen, root: shoot ratio, balanced activity     

Functional correlates of leaf demographic response to gap release in saplings of a shade-tolerant tree,<Emphasis Type="Italic"> Elateriospermum tapos</Emphasis>

For a shade-tolerant SE Asian tropical tree, Elateriospermum tapos (Euphorbiaceae), we studied field-established saplings in gaps and the shaded understory to test the hypothesis that differences in leaf demography and leaf life span under contrasting light regimes should be functionally correlated with architecture, self-shading and nitrogen distribution within the sapling crown. Rates of leaf production and net leaf gain were greater for saplings in gaps than those in the understory. Median leaf life span was approximately 26 months in the gap saplings, while it was estimated to be greater than 38 months in the understory saplings. Consequently, gap saplings had a greater standing leaf number and experienced greater degrees of self-shading than understory saplings. Light availability at individual leaves, estimated by a combination of canopy photos and a three-dimensional architecture model, were negatively correlated with leaf age in gap saplings but not so in understory saplings. Leaf nitrogen content per unit area (N_area) was influenced more by light availability than by leaf age in the gap saplings. In contrast, in understory saplings, N_area was neither correlated with light availability nor with leaf age, and did not decrease significantly before 38 months in leaf age. We conclude that saplings of this shade-tolerant species apparently prolong their leaf life span in the shaded understory through slower rates of leaf production, lower standing number of leaves and lower degrees of self shading than in gap, and that the rate of decline of N_area with leaf age depends on architecture and self-shading regimes that respond to changes in light regimes.     

Leaf age dependent changes in within-canopy variation in leaf functional traits: a meta-analysis

Within-canopy variation in leaf structural and photosynthetic characteristics is a major means by which whole canopy photosynthesis is maximized at given total canopy nitrogen. As key acclimatory modifications, leaf nitrogen content (N _A) and photosynthetic capacity (A _A) per unit area increase with increasing light availability in the canopy and these increases are associated with increases in leaf dry mass per unit area (M _A) and/or nitrogen content per dry mass and/or allocation. However, leaf functional characteristics change with increasing leaf age during leaf development and aging, but the importance of these alterations for within-canopy trait gradients is unknown. I conducted a meta-analysis based on 71 canopies that were sampled at different time periods or, in evergreens, included measurements for different-aged leaves to understand how within-canopy variations in leaf traits (trait plasticity) depend on leaf age. The analysis demonstrated that in evergreen woody species, M _A and N _A plasticity decreased with increasing leaf age, but the change in A _A plasticity was less suggesting a certain re-acclimation of A _A to altered light. In deciduous woody species, M _A and N _A gradients in flush-type species increased during leaf development and were almost invariable through the rest of the season, while in continuously leaf-forming species, the trait gradients increased constantly with increasing leaf age. In forbs, N _A plasticity increased, while in grasses, N _A plasticity decreased with increasing leaf age, reflecting life form differences in age-dependent changes in light availability and in nitrogen resorption for growth of generative organs. Although more work is needed to improve the coverage of age-dependent plasticity changes in some plant life forms, I argue that the age-dependent variation in trait plasticity uncovered in this study is large enough to warrant incorporation in simulations of canopy photosynthesis through the growing period.     

Biomass allocation and leaf chemical defence in defoliated seedlings of Quercus serrata with respect to carbon-nitrogen balance

BACKGROUND AND AIMS: Both nutrient availability and defoliation affect the carbon-nutrient balance in plants, which in turn influences biomass allocation (e.g. shoot-to-root ratio) and leaf chemical composition (concentration of nitrogen and secondary compounds). In this study it is questioned whether defoliation alters biomass allocation and chemical defence in a similar fashion to the response to nutrient deficiency. METHODS: Current-year seedlings of Quercus serrata were grown with or without removal of all leaves at three levels of nutrient availability. KEY RESULTS: Plant nitrogen concentration (PNC), a measure of the carbon-nutrient balance in the plant, significantly decreased immediately after defoliation because leaves had higher nitrogen concentrations than stems and roots. However, PNC recovered to levels similar to or higher than that of control plants in 3 or 6 weeks after the defoliation. Nitrogen concentration of leaves produced after defoliation was significantly higher than leaf nitrogen concentration of control leaves. Leaf mass per plant mass (leaf mass ratio, LMR) was positively correlated with PNC but the relationship was significantly different between defoliated and control plants. When compared at the same PNC, defoliated plants had a lower LMR. However, the ratio of the leaf to root tissues that were newly produced after defoliation as a function of PNC did not differ between defoliated and control plants. Defoliated plants had a significantly lower concentration of total phenolics and condensed tannins. Across defoliated and control plants, the leaf tannin concentration was negatively correlated with the leaf nitrogen concentration, suggesting that the amount of carbon-based defensive compounds was controlled by the carbon-nutrient balance at the leaf level. CONCLUSIONS: Defoliation alters biomass allocation and chemical defence through the carbon-nutrient balance at the plant and at the leaf level, respectively.     

Sagebrush carbon allocation patterns and grasshopper nutrition: the influence of CO2 enrichment and soil mineral limitation

Summary Artemisia tridentata seedlings were grown under carbon dioxide concentrations of 350 and 650 l l^–1 and two levels of soil nutrition. In the high nutrient treatment, increasing CO₂ led to a doubling of shoot mass, whereas nutrient limitation completely constrained the response to elevated CO₂. Root biomass was unaffected by any treatment. Plant root/shoot ratios declined under carbon dioxide enrichment but increased under low nutrient availability, thus the ratio was apparently controlled by changes in carbon allocation to shoot mass alone. Growth under CO₂ enrichment increased the starch concentrations of leaves grown under both nutrient regimes, while increased CO₂ and low nutrient availability acted in concert to reduce leaf nitrogen concentration and water content. Carbon dioxide enrichment and soil nutrient limitation both acted to increase the balance of leaf storage carbohydrate versus nitrogen (C/N). The two treatment effects were significantly interactive in that nutrient limitation slightly reduced the C/N balance among the high-CO₂ plants. Leaf volatile terpene concentration increased only in the nutrient limited plants and did not follow the overall increase in leaf C/N ratio. Grasshopper consumption was significantly greater on host leaves grown under CO₂ enrichment but was reduced on leaves grown under low nutrient availability. An overall negative relationship of consumption versus leaf volatile concentration suggests that terpenes may have been one of several important leaf characteristics limiting consumption of the low nutrient hosts. Digestibility of host leaves grown under the high CO₂ treatment was significantly increased and was related to high leaf starch content. Grasshopper growth efficiency (ECI) was significantly reduced by the nutrient limitation treatment but co-varied with leaf water content.     

Canopy structure and leaf nitrogen distribution in a stand of Lysimachia vulgaris L. as influenced by stand density

Summary A hypothesis that a dense stand should develop a less uniform distribution of leaf nitrogen through the canopy than an open stand to increase total canopy photosynthesis was tested with experimentally established stands of Lysimachia vulgaris L. The effect of stand density on spatial variation of photon flux density, leaf nitrogen and specific leaf weight within the canopy was examined. Stand density had little effect on the value of the light extinction coefficient, but strongly affected the distribution of leaf nitrogen per unit area within a canopy. The open stand had more uniform distribution of leaf nitrogen than the dense stand. However, different light climates between stands explained only part of the variation of leaf nitrogen in the canopy. The specific leaf weight in the canopy increased with increasing relative photon flux density and with decreasing nitrogen concentration.     

Photosynthetic light acclimation in two rainforest Piper species with different ecological amplitudes

Summary Piper auritum (H.B. & K.), a pioneer tree restricted to open sites and Piper hispidum (Swartz), a shrub common in sites ranging from recent clearings to shaded understory, both adjust photosynthetic characteristics in response to light availability during growth. The sensitivity of photosynthetic capacity to light availability during growth was indistinguishable for the two species growing in their natural habitat. Photosynthetic capacity was strongly correlated with leaf nitrogen in both species, and the relationship was similar between species. Dark respiration and leaf specific mass were more sensitive to light during growth in P. hispidum, the species with the broad habitat ange, than in P. auritum. In general, similarities between the species were more striking than differences between them. The differences in dark respiration could have important implications for carbon balance. The difference in the responsiveness of leaf specific mass to light indicates that the broad-ranging species maintains access to modes of response little utilized by the open-site specialist. We did not and, in the gas exchange characteristics, any evidence that the open site specialist is better suited than the generalist to high-light sites.This CIW DPB publication number 962     

云南文山石漠化区车桑子叶脉密度与叶氮含量关系对生境的响应

植物叶脉特征和叶氮含量的变化影响着叶片经济谱的形成,为验证叶片结构中叶脉网络构建提供了理论依据。该文以单位质量叶氮含量(N_(mass))和单位面积叶氮含量(N_(area))分别表示叶氮含量,采取主成分分析、线性回归分析的方法,研究了云南文山石漠化区旷地(Ⅰ)、林缘(Ⅱ)和林下(Ⅲ)3种自然生境下车桑子的叶脉密度(Vein density,VD)与N_(mass)和N_(area)的异速关系。结果表明:从乔灌群落的旷地到林下,车桑子的比叶面积、叶绿素总含量、光能利用率和N_(mass)逐渐增大,光饱和点、光补偿点、水分利用效率、VD、N_(area)逐渐减小,净光合速率、蒸腾速率、气孔导度呈先增大后减小的趋势。VD与叶氮含量呈不同程度的相关性,在生境I和III,VD与N_(mass)和N_(area)分别具有显著的负相关(P0.05)和正相关(P0.05);在生境Ⅱ,VD与N_(mass)和N_(area)分别呈不显著负相关(P0.05)和正相关(P0.05)。车桑子在旷地强光生境,高VD的叶片含有低N_(mass)高N_(area),而林下荫蔽生境偏向于相反的配置模式,反映了石漠化区植物较强的叶脉可塑性及其与氮利用性状的权衡机制。     

刨花楠不同相对生长速率下林木叶片碳氮磷的适应特征

分别对9年生与13年生刨花楠林木叶片氮磷养分之间关系及林木生物量相对生长速率与叶片碳氮磷化学计量比关系进行分析,探讨不同相对生长速率下的林木叶片N、P养分适应特征,并检验相对生长速率假说理论对刨花楠树种的适应性。结果表明:两种年龄刨花楠林木生物量相对生长速率、叶片C、N、P含量及其计量比值均存在显著差异;同一年龄的林木叶片N、P之间存在显著相关性,二者具有协同相关性;9年生林木叶片P含量及C∶P、N∶P与生物量相对生长速率呈二次曲线相关,而13年生林木叶片N、P含量及C∶N、C∶P、N∶P则与生物量相对生长速率均呈线性相关。研究表明,在能满足植物生长所需养分供给的土壤环境中,叶片N、P含量与林木相对生长速率间呈线性正相关,但当土壤中养分供应满足不了植物高速生长时,植物则会对有限的养分资源进行适应性调整。