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1.
Does the photosynthetic light‐acclimation need change in leaf anatomy?   总被引:23,自引:3,他引:20  
There is a strong correlation between leaf thickness and the light‐saturated rate of photosynthesis per unit leaf area (Pmax). However, when leaves are exposed to higher light intensities after maturation, Pmax often increases without increasing leaf thickness. To elucidate the mechanism with which mature leaves increase Pmax, the change in anatomical and physiological characteristics of mature leaves of Chenopodium album, which was transferred from low to high light condition, were examined. When compared with leaves subjected to low light continuously (LL leaves), the leaves transferred from low to high light (LH leaves) significantly increased Pmax. The transfer also increased the area of chloroplasts facing the intercellular space (Sc) and maintained a strong correlation between Pmax and Sc. The mesophyll cells of LL leaves had open spaces along cell walls where chloroplasts were absent, which enabled the leaves to increase Pmax when they were exposed to high light (LH). However, the LH leaves were not thick enough to allow further increase in Pmax to the level in HH leaves. Thus leaf thickness determines an upper limit of Pmax of leaves subjected to a change from low to high light conditions. Shade leaves would only increase Pmax when they have open space to accommodate chloroplasts which elongate after light conditions improve.  相似文献   
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3.
Photosynthetic nitrogen use efficiency (PNUE, photosynthetic capacity per unit leaf nitrogen) is one of the most important factors for the interspecific variation in photosynthetic capacity. PNUE was analysed in two evergreen and two deciduous species of the genus Quercus. PNUE was lower in evergreen than in deciduous species, which was primarily ascribed to a smaller fraction of nitrogen allocated to the photosynthetic apparatus in evergreen species. Leaf nitrogen was further analysed into proteins in the water‐soluble, the detergent‐soluble, and the detergent‐insoluble fractions. It was assumed that the detergent‐insoluble protein represented the cell wall proteins. The fraction of nitrogen allocated to the detergent‐insoluble protein was greater in evergreen than in deciduous leaves. Thus the smaller allocation of nitrogen to the photosynthetic apparatus in evergreen species was associated with the greater allocation to cell walls. Across species, the fraction of nitrogen in detergent‐insoluble proteins was positively correlated with leaf mass per area, whereas that in the photosynthetic proteins was negatively correlated. There may be a trade‐off in nitrogen partitioning between components pertaining to productivity (photosynthetic proteins) and those pertaining to persistence (structural proteins). This trade‐off may result in the convergence of leaf traits, where species with a longer leaf life‐span have a greater leaf mass per area, lower photosynthetic capacity, and lower PNUE regardless of life form, phyllogeny, and biome.  相似文献   
4.
A model of leaf photosynthesis of C3, plants has been developed to describe their nitrogen economy. In this model, photosynthetic proteins are categorized into five groups depending on their functions. The effects of investment of nitrogen in each of these groups on the maximal rate of photosynthesis and/or the initial slope of the light-response curve are described as simple equations. Using this model, the optimal pattern of nitrogen partitioning which maximizes the daily rate of CO2 exchange is estimated for various light environments and leaf nitrogen contents. When the leaf nitrogen content is fixed, the amount of nitrogen allocated to Calvin cycle enzymes and electron carriers increases with increasing irradiance, while that allocated to chlorophyll-protein complexes increases with decreasing irradiance. For chlorophyll-proteins of photosystem II, the amount of light-harvesting complex II relative to that of the core complex increases with decreasing irradiance. At any irradiance, partitioning into ribulose bisphosphate carboxylase increases with increasing leaf nitrogen content Taking the total leaf nitrogen content and the daily CO2 exchange rate as ‘cost’ and ‘benefit’, respectively, the optimal amount and partitioning of nitrogen are examined for various conditions of light environment and nitrogen availability. The leaf nitrogen content that maximizes the rate of daily carbon fixation increases with increasing growth irradiance. It is also predicted that, at low nitrogen availabilities, low leaf nitrogen contents are advantageous in terms, of nitrogen use efficiency. These trends predicted by the present model are largely consistent with those reported for actual plants. The differences in the total amount of leaf nitrogen and in the organization of photosynthetic components that have been reported for plants from different environments would therefore be of adaptive significance, because such differences can contribute to realization of efficient photosynthesis. These results are fürther discussed in an ecological context.  相似文献   
5.
To investigate the effect of elevated CO2 on the size inequality and size structure, even‐aged monospecific stands of an annual, Chenopodium album, were established at ambient and doubled CO2 with high and low nutrient availabilities in open top chambers. The growth of individual plants was monitored non‐destructively every week until flowering. Elevated CO2 significantly enhanced plant growth at high nutrients, but did not at low nutrients. The size inequality expressed as the coefficient of variation tended to increase at elevated CO2. Size structure of the stands was analyzed by the cumulative frequency distribution of plant size. At early stages of plant growth, CO2 elevation benefited all individuals and shifted the whole size distribution of the stand to large size classes. At later stages, dominant individuals were still larger at elevated than at ambient CO2, but the difference in small subordinate individuals between two CO2 levels became smaller. Although these tendencies were found at both nutrient availabilities, difference in size distribution between CO2 levels was larger at high nutrients. The CO2 elevation did not significantly enhance the growth rate as a function of plant size except for the high nutrient stand at the earliest stage, indicating that the higher biomass at elevated CO2 at later stages in the high nutrient stand was caused by the larger size of individuals at the earliest stage. Thus the effect of elevated CO2 on stand structure and size inequality strongly depended on the growth stage and nutrient availabilities.  相似文献   
6.
Comparative ecophysiology of leaf and canopy photosynthesis   总被引:22,自引:7,他引:15  
Leaves and herbaceous leaf canopies photosynthesize efficiently although the distribution of light, the ultimate resource of photosynthesis, is very biased in these systems. As has been suggested in theoretical studies, if a photosynthetic system is organized such that every photosynthetic apparatus photosynthesizes in concert, the system as a whole has the sharpest light response curve and is most adaptive. This condition can be approached by (i) homogenization of the light environment and (ii) acclimation of the photosynthetic properties of leaves or chloroplasts to their local light environments. This review examines these two factors in the herbaceous leaf canopy and in the leaf. Changes in the inclination of leaves in the canopy and differentiation of mesophyll into palisade and spongy tissue contribute to the moderation of the light gradient. Leaf and chloroplast movements in the upper parts of these systems under high irradiances also moderate light gradients. Moreover, acclimation of leaves and chloroplasts to the local light environment is substantial. These factors increase the efficiency of photosynthesis considerably. However, the systems appear to be less efficient than the theoretical optimum. When the systems are optically dense, the light gradients may be too great for leaves or chloroplasts to acclimate. The loss of photosynthetic production attributed to the imperfect adjustment of photosynthetic apparatus to the local light environment is most apparent when the photosynthesis of the system is in the transition between the light-limited and light-saturated phases. Although acclimation of the photosynthetic apparatus and moderation of light gradients are imperfect, these markedly raise the efficiency of photosynthesis. Thus more mechanistic studies on these adaptive attributes are needed. The causes and consequences of imperfect adjustment should also be investigated.  相似文献   
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Elevated atmospheric CO2 concentration ([CO2]) stimulates seed mass production in many species, but the extent of stimulation shows large variation among species. We examined (1) whether seed production is enhanced more in species with lower seed nitrogen concentrations, and (2) whether seed production is enhanced by elevated [CO2] when the plant uses more N for seed production. We grew 11 annuals in open top chambers that have different [CO2] conditions (ambient: 370 μmol mol−1, elevated: 700 μmol mol−1). Elevated [CO2] significantly increased seed production in six out of 11 species with a large interspecific variation (0.84–2.12, elevated/ambient [CO2]). Seed nitrogen concentration was not correlated with the enhancement of seed production by elevated [CO2]. The enhancement of seed production was strongly correlated with the enhancement of seed nitrogen per plant caused by increased N acquisition during the reproductive period. In particular, legume species tended to acquire more N and produced more seeds at elevated [CO2] than non-nitrogen fixing species. Elevated [CO2] little affected seed [N] in all species. We conclude that seed production is limited primarily by nitrogen availability and will be enhanced by elevated [CO2] only when the plant is able to increase nitrogen acquisition.  相似文献   
8.
Interspecific variation in the response to transfer from low to high growth irradiance with respect to anatomical and photosynthetic characteristics was studied in mature leaves of three tree species, Betula ermanii Cham., Acer rufinerve Sieb. et Zucc. and Fagus crenata Blume, which occur in different successional stages in temperate deciduous forests. Transfer from low to high irradiance increased the light-saturated rate of photosynthesis per unit leaf area ( P max) significantly in B. ermanii and A. rufinerve , but not in F. crenata . Leaves of B. ermanii grown at low irradiance were relatively thick and had vacant spaces along the mesophyll cell surfaces which was not occupied by chloroplasts or other organelles. After transfer to high irradiance, chloroplasts enlarged to fill the space along with P max without an increase in leaf thickness. Leaves of A. rufinerve were plastic in mesophyll cell surface area and in leaf thickness, both of which increased after the transfer to high irradiance, along with an increase in the amount of chloroplasts and in P max. On the other hand, F. crenata had little mesophyll cell surface unoccupied by chloroplasts and leaf anatomy was not changed after the transfer. In all species, P max was strongly correlated with chloroplast surface area adjacent to the exposed mesophyll surface across different growth irradiances. An increase in P max was observed only when chloroplast volume also increased. We conclude that light acclimation potential is primarily determined by the availability of unoccupied cell surface into which chloroplasts expand, as well as by the plasticity of the mesophyll that allows an increase in its surface area.  相似文献   
9.
HIKOSAKA  KOUKI 《Annals of botany》1997,80(6):721-730
A new hypothesis for temperature acclimation by the photosyntheticapparatus is presented. An optimization model is developed toexamined effects of changes in the organization of photosyntheticcomponents on leaf photosynthesis under various growth temperatureswhere the photosynthetic apparatus is not damaged. In this model,photosynthetic rate is limited either by the capacity of ribulosebisphosphate carboxylase (RuBPCase) to consume ribulose bisphosphate(RuBP), or by the capacity of RuBP regeneration. For temperaturedependence of the RuBPCase activity, data fromSpinacia oleraceaL.,which have a temperature optimum of 30 °C, are used. Fortemperature dependence of the capacity of RuBP regeneration,two contrasting curves that have temperature optima of 30 °C(Eucalyptus paucifloraSieb. ex Spreng) and 40 °C (LarreadivaricataCav.) are applied. The temperature dependence of eachprocess is fixed for respective species, but the rate of eachprocess varies with changes in the amounts of components. Thecost of proteins, in terms of nitrogen, required to carry outeach process is calculated when nitrogen is partitioned differentlyamong photosynthetic components. The optimal nitrogen partitioningthat maximizes daily photosynthesis at a given temperature isobtained. The predicted temperature optimum of the photosyntheticrate inLarrea divaricataexhibits large shifts with changes intarget temperature, while shifts are negligible inEucalyptuspauciflora. It is suggested that the shift in temperature optimumof photosynthetic rate is large when the temperature dependencesof the capacities of RuBPCase and RuBP regeneration differ fromeach other.Copyright 1997 Annals of Botany Company Optimization model; nitrogen use efficiency; photosynthetic acclimation; temperature dependence  相似文献   
10.
Nitrogen distribution within a leaf canopy is an important determinant of canopy carbon gain. Previous theoretical studies have predicted that canopy photosynthesis is maximized when the amount of photosynthetic nitrogen is proportionally allocated to the absorbed light. However, most of such studies used a simple Beer's law for light extinction to calculate optimal distribution, and it is not known whether this holds true when direct and diffuse light are considered together. Here, using an analytical solution and model simulations, optimal nitrogen distribution is shown to be very different between models using Beer's law and direct–diffuse light. The presented results demonstrate that optimal nitrogen distribution under direct–diffuse light is steeper than that under diffuse light only. The whole‐canopy carbon gain is considerably increased by optimizing nitrogen distribution compared with that in actual canopies in which nitrogen distribution is not optimized. This suggests that optimization of nitrogen distribution can be an effective target trait for improving plant productivity.  相似文献   
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