A model of daily canopy photosynthesis was constructed taking light and leaf nitrogen distribution in the canopy into consideration. It was applied to a canopy of Solidago altissima. Both irradiance and nitrogen concentration per unit leaf area decreased exponentially with increasing cumulative leaf area from the top of the canopy. The photosynthetic capacity of a single leaf was evaluated in relation to irradiance and nitrogen concentration. By integration, daily canopy photosynthesis was calculated for various canopy architectures and nitrogen allocation patterns. The optimal pattern of nitrogen distribution that maximizes the canopy photosynthesis was determined. Actual distribution of leaf nitrogen in the canopy was more uniform than the optimal one, but it realized over 20% more photosynthesis than that under uniform distribution and 4.7% less photosynthesis than that under the optimal distribution. Redeployment of leaf nitrogen to the top of the canopy with ageing should be more effective in increasing total canopy photosynthesis in a stand with a dense canopy than in a stand with an open canopy.

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 detergentinsoluble fractions. It was assumed that the detergentinsoluble 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.

There is a strong correlation between leaf thickness and the light-saturated rate of photosynthesis per unit leaf area ( P max ). However, when leaves are exposed to higher light intensities after maturation, P max often increases without increasing leaf thickness. To elucidate the mechanism with which mature leaves increase P max , 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 P max . The transfer also increased the area of chloroplasts facing the intercellular space ( S c ) and maintained a strong correlation between P max and S c . The mesophyll cells of LL leaves had open spaces along cell walls where chloroplasts were absent, which enabled the leaves to increase P max when they were exposed to high light (LH). However, the LH leaves were not thick enough to allow further increase in P max to the level in HH leaves. Thus leaf thickness determines an upper limit of P max of leaves subjected to a change from low to high light conditions. Shade leaves would only increase P max when they have open space to accommodate chloroplasts which elongate after light conditions improve.

Summary1. Nitrogen (N) is an essential limiting resource for plant growth, and its efficient use may increase fitness. We investigated photosynthetic N-use efficiency (photosynthetic capacity per unit N) in relation to N allocation to Rubisco and to cell walls in Polygonum cuspidatum Sieb. et Zucc. which germinated in May (early germinators) and August (late germinators). 2. There was a significant difference between early and late germinators in photosynthetic capacity as a function of leaf N content per unit area. Higher photosynthetic N-use efficiency in late germinators was caused primarily by a larger allocation of N to Rubisco. 3. Nitrogen allocation to cell walls was smaller in late germinators. The shorter growth period in late germinators was associated with higher photosynthetic capacity, which was achieved by allocating more N to photosynthetic proteins at the expense of cell walls. 4. The trade-off between N allocation to photosynthesis and to structural tissues suggests that plants change N allocation to increase either the rate or duration of carbon assimilation. Such plastic change would help plants maintain themselves and cope with environmental changes.

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.Key-words : acclimation potential; chloroplasts; leaf anatomy; leaf nitrogen; mature leaves; photosynthetic capacity; sun/ shade acclimation; transfer experiment.

Photosynthetic capacity was measured on detached leaves sampled in a canopy of Solidago altissima L. Non‐rectangular hyperbola fitted the light response curve of photosynthesis and significant correlations were observed between leaf nitrogen per unit area and four parameters which characterize the light‐response curve. Using regressions of the parameters on leaf nitrogen, a model of leaf photosynthesis was constructed which gave the relationships between leaf nitrogen, photon flux density (PFD) and photosynthesis. Curvilinear relations were obtained between leaf nitrogen and photosynthetic rate on both an instantaneous and a daily basis. Nitrogen use efficiency (NUE, photosynthesis per unit leaf nitrogen) was calculated against leaf nitrogen under varying PFDs. The optimum nitrogen content per unit leaf area that maximizes NUE shifted to higher values with increasing PFD. Field measurements of PFD showed high positive correlations between the distribution of leaf nitrogen in the canopy and relative PFD. The predicted optimum leaf nitrogen content for each level in the canopy, to achieve maximized NUE during a clear day, was close to the actual nitrogen distribution as found through sampling.

Summary0 We compared allometric growth patterns\ canopy structure and light interception for individual shoots of di}erent species in a tall!grass meadow[ 1 The vertical distributions of above!ground biomass\ leaf area\ height and leaf angles were measured\ both early and late in the season\ for individual shoots of Miscanthus sinensis "the dominant species#\ Lespedeza bicolor\ Lysimachia clethroides\ Astilbe thunber`ii and Potentilla freyniana[ A canopy model was developed to calculate light absorption by individual shoots[ Light absorption per unit mass "F mass # was used to quantify the e.ciency with which plants utilized biomass to capture light[ 2 The leaf mass ratio "LMR#\ average speci_c leaf area "SLA# and therefore the leaf area ratio "LAR# decreased with shoot height and light availability[ Light absorption per unit leaf area "F area # increased with shoot height\ and this increase was observed to be much stronger at greater than at smaller shoot heights[ 3 In the taller species "Miscanthus and Lespedeza# F mass "the product of LAR and F area # increased\ while in the shortest species "Potentilla# it decreased with shoot height[ Clones of Miscanthus and Lespedeza may thus increase total light capture by allocating shoot biomass among fewer taller shoots\ and a clone of Potentilla by producing a larger number of shorter shoots[ 4 Shoots of the shorter species were equally e.cient in capturing light "i[e[ they had similar F mass # early in the season\ but less e.cient later in the season than shoots of the taller species[ Shorter species appear to be able to use the earlier part of the season for e.cient light capture\ while shoots of taller species gain an advantage from their height later in the season[ 5 This study shows how di}erent above!ground growth patterns of the species in a tall!grass meadow allow them to use di}erent positions in vertical space and di}erent periods of the season to absorb light e.ciently[ This is a clear example of niche separation and helps to explain the coexistence of these species[ Keywords] allometry\ canopy model\ coexistence\ Miscanthus sinensis\ niche sep! aration Journal of Ecolo`y "0888# 76\ 472Ð486

This paper demonstrates a new analysis of photon flux partitioning among species and an evaluation of the efficiency of photon flux capturing in terms of biomass investment. For that purpose, distributions of aboveground biomass, leaf area, and photon flux density (PPFD) were determined with the stratified harvest method in a stand of a tall herbaceous community on a floating fen at the time of peak standing crop. The stand contained 11 species and the photon flux absorbed by each species in the stand was estimated. Three tall dominant species absorbed 75% of the incident PPFD, while eight short subordinate species absorbed 2.5%. Tall species in the canopy received higher PPFD averaged over leaf area (°area). However, the PPFD absorbed per unit aboveground biomass (°mass) of the tall species was not higher than that of the subordinate species. °mass is a product of the leaf area ratio (LAR, the ratio of leaf area to aboveground biomass) and °area. There was a trade—off relationship between LAR and °area. To have a high °area, plants place their leaves at higher positions in the canopy, which necessarily decreases LAR. Aboveground biomass was regarded as an investment (cost) to capture PPFD (benefit). °mass, as a ratio of benefit to cost, indicates an efficiency of biomass investment to capture photon flux. Tall species appeared to have an advantage over subordinate species in receiving a large fraction of incident PPFD, while subordinate species have an advantage in efficiently using their biomass to capture PPFD.