Changes in Size and Number of Mesophyll Cells, Nitrogen Content and Photosynthesis with Leaf Order in Brassica spp.

Numbers of mesophyll cells per unit leaf area decreased progressivelyfrom an upper leaf with a width of 3 cm towards the lower leaves.Enlargement of mesophyll cell size with leaf order accountedfor an increase or maintenance of mesophyll cell surface areaper unit leaf area. Increase of photosynthetic rates was correlatedwith increases of mesophyll cell surface area and nitrogen contentper unit leaf area. Therefore, in spite of an increase in cellsurface area to volume ratio with increase of mesophyll cellsize, it appears that increase of mesophyll cell surface areaand nitrogen content per unit leaf area enables a high rateof photosynthesis to be maintained. Brassica, photosynthesis, mesophyll surface area, nitrogen content, cell size, mesophyll resistance, leaf age     

The diurnal time course of net photosynthesis of soybean leaves: Analysis with a physiologically based steady-state photosynthesis model

Summary A physiologically based steady-state model of whole leaf photosynthesis (WHOLEPHOT) is used to analyze observed net photosynthesis daily time courses of soybean, Glycine max (L.) Merr., leaves. Observations during two time periods of the 1978 growing season are analyzed and compared. After adjustment of the model for soybean, net photosynthesis rates are calculated with the model in response to measured incident light intensity, leaf temperature, air carbon dioxide concentration, and leaf diffusion resistance. The steady-state calculations closely approximate observed net photosynthesis. Results of the comparison reveal a decrease in photosynthetic capacity in leaves sampled during the second time period, which is associated with decreasing ability of leaves to respond to light intensity and internal air space carbon dioxide concentration, increasing mesophyll resistance, and increasing stomatal resistance.     

Effects of Polyploidy on Photosynthetic Rates, Photosynthetic Enzymes, Contents of DNA, Chlorophyll, and Sizes and Numbers of Photosynthetic Cells in the C(4) Dicot Atriplex confertifolia

Photosynthetic rates, chlorophyll content, and activities of several photosynthetic enzymes were determined per cell, per unit DNA, and per unit leaf area in five ploidal levels of the C₄ dicot Atriplex confertifolia. Volumes of bundle sheath and mesophyll protoplasts were measured in enzymatic digestions of leaf tissue. Photosynthetic rates per cell, contents of DNA per cell, and activities of the bundle sheath enzymes ribulose 1,5-bisphosphate carboxylase (RuBPC) and NAD-malic enzyme per cell were correlated with ploidal level at 99% or 95% confidence levels, and the results suggested a near proportional relationship between gene dosage and gene products. There was also a high correlation between volume of mesophyll and bundle sheath cells and the ploidal level. Contents of DNA per cell, activity of RuBPC per cell, and volumes of cells were correlated with photosynthetic rate per cell at the 95% confidence level. The mesophyll cells did not respond to changes in ploidy like the bundle sheath cells. In the mesophyll cells the chlorophyll content per cell was constant at different ploidal levels, there was less increase in cell volume than in bundle sheath cells with an increase in ploidy, and there was not a significant correlation (at 95% level) of phosphoenolpyruvate carboxylase activity or content and pyruvate,Pi dikinase activity with increase in ploidy. The number of photosynthetic cells per unit leaf area progressively decreased with increasing ploidy from diploid to hexaploid, but thereafter remained constant in octaploid and decaploid plants. Numbers of cells per leaf area were not correlated with cell volumes. The mean photosynthetic rates per unit leaf area were lowest in the diploid, similar in 4×, 6×, and 8×, and highest in the decaploid. The photosynthetic rate per leaf area was highly correlated with the DNA content per leaf area.     

Adaptations of the Photosynthetic Mechanism of Sugar Maple (Acer saccharum) Seedlings Grown in Various Light Intensities

Sugar maple (Acer saccharum Marsh.) seedlings were grown in a nursery for three years in 13, 25, 45 and 100 per cent of full daylight. During the third year of growth, the rates of their apparent photosynthesis and respiration were measured periodically with an infra-red gas analyzer at various light intensities and normal CO₂ concentration. In addition, the rates of apparent photosynthesis of a single attached leaf of the same seedlings were measured at saturating light intensity, hut varying CO₂ concentrations. An increase in the light intensity in which seedlings were grown had no effect on their height or mean leaf area, hut resulted in thicker leaves, an increase in the total leaf area per seedling due to an increase in the number of leaves, an increase in the dry weight especially of roots and a decrease in the chlorophyll content of leaves. Throughout the growing season seedlings grown in full daylight, as compared with those grown in lower light intensities, had the lowest rates of apparent photosynthesis measured at standard conditions (21,600 lux light intensity and 300 ul/l of CO₂), when this was expressed per unit leaf area, hut the highest rates on a per seedling basis. Thus dry matter production attained at the end of the growing season correlated positively with the photosynthetic rate per seedling, but not per unit leaf area. The rates of apparent photosynthesis of seedlings grown at lower light intensities were more responsive to changes in light intensity or CO₂ concentration than those of seedlings grown in full daylight intensity.     

Photosynthetic characteristics of leaves developed at different irradiances and temperatures: an extension of the current hypothesis

Photosynthetic characteristics at high measurement irradiance were analyzed for single leaves of two C₃ and one C₄ species grown under twenty one combinations of irradiance level, irradiance duration, and air temperature in order to test the idea that photosynthetic characteristies developed by leaves in different environments are controlled by the daily amount of photosynthesis. Photosynthetic rates per unit area and mesophyll conductances at 25°C and air levels of CO₂ and O₂, and parameters for two photosynthesis models were used to characterize the photosynthetic properties of the leaves. Leaves with highest values of the photosynthetic parameters for each species were often developed in environments with irradiance levels below saturation for photosynthesis, and with only 12 hours of irradiance per day. Lower air temperature during growth increased the photosynthetic characteristics for a given irradiance regime. Photosynthetic characteristics had higher correlation coefficients with daily photosynthesis of mature leaves divided by 24-hour leaf elongation rates of young leaves, than with daily photosynthesis alone, indicating that photosynthetic characteristics may be related to a balance between photosynthesis and leaf expansion.     

Photosynthetic characteristics of leaves developed at different irradiances and temperatures: an extension of the current hypothesis.

Photosynthetic characteristics at high measurement irradiance were analyzed for single leaves of two C₃ and one C₄ species grown under twenty one combinations of irradiance level, irradiance duration, and air temperature in order to test the idea that photosynthetic characteristics developed by leaves in different environments are controlled by the daily amount of photosynthesis. Photosynthetic rates per unit area and mesophyll conductances at 25°C and air levels of CO₂ and O₂, and parameters for two photosynthesis models were used to characterize the photosynthetic properties of the leaves. Leaves with highest values of the photosynthetic parameters for each species were often developed in environments with irradiance levels below saturation for photosynthesis, and with only 12 hours of iradiance per day. Lower air temperature during growth increased the photosynthetic characteristics for a given irradiance regime. Photosynthetic characteristics had higher correlation coefficients with daily photosynthesis of mature leaves divided by 24-hour leaf elongation rates of young leaves, than with daily photosynthesis alone, indicating that photosynthetic characteristics may be related to a balance between photosynthesis and leaf expansion.     

Structure of the Photosynthetic Apparatus in Leaves of Freshwater Hydrophytes: 2. Quantitative Characterization of Leaf Mesophyll and the Functional Activity of Leaves with Different Degrees of Submersion

The structure of leaf photosynthetic elements was investigated on 42 boreal plant species characterized by different degrees of submergence (helophytes, neustophytes, and hydatophytes). Six main types of mesophyll structures were identified. Quantitative characteristics for the mesostructure of the photosynthetic apparatus in these groups were determined, such as the size and abundance of cells and chloroplasts in the mesophyll and epidermis, the number of plastids per cell in each tissue, the total surface area of the mesophyll cells, epidermal cells, and chloroplasts per unit leaf area. Analysis showed that quantitative characteristics of the photosynthetic apparatus in hydrophytes are determined by two factors: (a) the degree of leaf submergence and (b) the type of mesophyll structure. With an increasing degree of immersion in water, the mesophyll types change in a sequence isopalisade dorsoventral homogeneous. The leaves become thinner, their weight per unit area diminishes, cells and chloroplasts become less numerous (on a per unit leaf area basis), but their dimensions become larger. Adaptation to aquatic medium is also manifested in the increasing contribution of the epidermal tissue to the overall photosynthesis: in submerged leaves, the epidermis accounts for more than 50% of the photosynthetic activity. The occurrence of six structural types of leaves contrasting in their characteristics was confirmed by discriminatory analysis according to the qualitative parameters of mesophyll.     

Effect of solar ultraviolet-B radiation during springtime ozone depletion on photosynthesis and biomass production of Antarctic vascular plants

We assessed the influence of springtime solar UV-B radiation that was naturally enhanced during several days due to ozone depletion on biomass production and photosynthesis of vascular plants along the Antarctic Peninsula. Naturally growing plants of Colobanthus quitensis (Kunth) Bartl. and Deschampsia antarctica Desv. were potted and grown under filters that absorbed or transmitted most solar UV-B. Plants exposed to solar UV-B from mid-October to early January produced 11% to 22% less total, as well as above ground biomass, and 24% to 31% less total leaf area. These growth reductions did not appear to be associated with reductions in photosynthesis per se: Although rates of photosynthetic O(2) evolution were reduced on a chlorophyll and a dry-mass basis, on a leaf area basis they were not affected by UV-B exposure. Leaves on plants exposed to UV-B were denser, probably thicker, and had higher concentrations of photosynthetic and UV-B absorbing pigments. We suspect that the development of thicker leaves containing more photosynthetic and screening pigments allowed these plants to maintain their photosynthetic rates per unit leaf area. Exposure to UV-B led to reductions in quantum yield of photosystem II, based on fluorescence measurements of adaxial leaf surfaces, and we suspect that UV-B impaired photosynthesis in the upper mesophyll of leaves. Because the ratio of variable to maximal fluorescence, as well as the initial slope of the photosynthetic light response, were unaffected by UV-B exposure, we suggest that impairments in photosynthesis in the upper mesophyll were associated with light-independent enzymatic, rather than photosystem II, limitations.     

Variation of photosynthetic capacity with leaf age in an alpine orchid, Cypripedium flavum

Photosynthetic rate, chlorophyll fluorescence, leaf nitrogen and chlorophyll content of Cypripedium flavum were studied at different leaf ages. The photosynthetic capacity changed significantly with leaf age. Net photosynthesis and chlorophyll content peaked when leaf age was 60 days, decreasing at 30, 90 and 120 days. Stomatal conductance showed the highest value at 60 days, while mesophyll conductance decreased with increasing leaf age. Both leaf nitrogen content per unit area and leaf nitrogen content per unit mass decreased with increasing leaf age. The age-dependent variation in photosynthetic capacity could be linked to the changes in biochemical efficiency, leaf nitrogen content and CO₂ diffusion limitation.     

Changes in the photosynthetic apparatus of maize in response to simulated natural temperature fluctuations

The response of the photosynthetic apparatus to low temperature periods differed among three hybrids of maize (Zea mays L.) grown in a phytotron. Light-saturated photosynthetic rates, leaf chlorophyll content, and mesophyll cell photosynthetic unit density all declined with increasing duration of low temperature. No single metabolic or physiological parameter appeared to control the response of the three hybrids to low temperature stress. Among all temperature treatments, net photosynthetic rate on a leaf area basis was more closely correlated with leaf chlorophyll content than with any other measured parameter. Final shoot dry weight was most highly correlated with stomatal conductance to CO₂.     

Improved growth and water use efficiency of cherry saplings under reduced light intensity

Cherry (Prunus avium L.) saplings were grown under natural sunlight (controls) or moderate shading (up to 30%, depending on the incident light intensity and the hour of the day). Reduced light intensity increased the dry mass of each of the plant components studied. Consequently, the total dry mass of shaded plants was significantly greater than that of controls at the end of the growing season. However, the diurnal trend in the level of photosynthesis (per unit of leaf area) of shaded plants was similar to the controls in August, but lower in September. As the growing season proceeded, reduced photosynthetic rates, thinner mesophyll and larger specific leaf area in the shaded plants indicated that leaf development had adapted to shaded conditions throughout the growing season. It is suggested that increased growth of shaded plants was caused by a higher initial relative growth rate and a greater whole-plant photosynthesis. Shading consistently reduced transpiration over the season, therefore improving water use efficiency of shaded leaves. Our results suggest that a moderate reduction in light intensity can be a useful method for improving growth and saving water in hot and dry environments.     

Ecophysiological studies of sonoran Desert plants

Summary Photosynthetic responses to light and temperature are compared for two genetically related chromosomal races of Machaeranthera gracilis. The ancestral foothills race occurs in cooler, more mesic environments, while the derived desert race occurs in more arid environments. The desert race exhibited greater rates of net photosynthesis at all levels of irradiance than did plants of the foothills race. This enhancement is due primarily to a greater quantum yield and leaf density. High light pretreatment significantly increased the photosynthetic capacity of the desert race, with little or no effect on the foothills race. Furthermore, the leaf density of the desert race was affected proportionately more than the foothills race by light pretreatment. The desert race also possessed higher stomatal and mesophyll conductances to CO₂. Both races exhibited enhanced photosynthetic capacities when grown in a warm thermoperiod (35/25 C), relative to a cool thermoperiod (25/15 C), concomitant with slight increases in leaf density. There was a lack of thermal acclimation for both photosynthesis and respiration of the two races. The greater photosynthetic capactity of the desert race is suggested as an evolutionary modification which could account for invasion into and survival in the sonoran Desert.     

Leaf Factors Affecting Light-Saturated Photosynthesis in Ecotypes of Solidago virgaurea from Exposed and Shaded Habitats

Plants of Solidago virgaurea L. from exposed and shaded habitats differ with respect to the response of the photosynthetic apparatus to the level of irradiance during growth. An analysis was carried out on leaf characteristies which might be responsible for the differences established in the rates of Hght-saturated CO₂ uptake. The clones were grown in controlled environment chambers at high and low levels of irradiance. Light-saturated rates of photosynthesis and transpiration were measured at natural and lower ambient CO₂ concentrations. A low temperature dependence of light-saturated CO₂ uptake at natural CO₂ concentrations, and a strong response to changes in stomatal width, suggested that the rate of CO₂ transfer from ambient air towards reaetion sites in chloroplasts was mainly limiting the pholosynthetic rate. Resistances to transfer of CO₂ for different parts of the pathway were calculated. There was a weak but significant correlation between stomatal conductance and the product stomatal frequency ± pore length. Mesopbyll conductance and dry weight per unit area were highly correlated in leaves not damaged by high irradiance. This suggests that mesophyll conductance increases with increasing cross sectional area (per unit leaf area) of the pathways of CO₂ transfer in the mesophyll from cell surfaces to reaction sites. The higher light-saturated photosynthesis in clones from exposed habitats when grown at high irradiance than when grown at low irradiance was attributable mainly to a lower mesophyll resistance. In shade clones the effect upon CO₂ uptake of the increase in leaf thickness when grown at high irradiance was counteracted by the associated inactivation of the photosynthetic apparatus. The difference in CO₂ uptake present between clones from exposed and shaded habitats when preconditioned to high irradiance resulted from differences in both mesophyll and stomatal resistances. A few hybrid clones of an F₁-population from a cross between a clone from an exposed habitat and a clone from a shaded habitat reacted, on the whole, in the same way as the exposed habitat parent. When grown at high irradiance, the hybrid clones showed higher photosynthetic rates than either parent; this was largely attributable to the unusually low stomatal resistance of the hybrid leaves.     

Activation of NADP-Malate Dehydrogenase, Pyruvate,Pi Dikinase, and Fructose 1,6-Bisphosphatase in Relation to Photosynthetic Rate in Maize

The activity and extent of light activation of three photosynthetic enzymes, pyruvate,Pi dikinase, NADP-malate dehydrogenase (NADP-MDH), and fructose 1,6-bisphosphatase (FBPase), were examined in maize (Zea mays var Royal Crest) leaves relative to the rate of photosynthesis during induction and under varying light intensities. There was a strong light activation of NADP-MDH and pyruvate,Pi dikinase, and light also activated FBPase 2- to 4-fold. During the induction period for whole leaf photosynthesis at 30°C under high light, the time required to reach half-maximum activation for all three enzymes was only 1 minute or less. After 2.5 minutes of illumination the enzymes were fully activated, while the photosynthetic rate was only at half-maximum activity, indicating that factors other than enzyme activation limit photosynthesis during the induction period in C₄ plants.

Under steady state conditions, the light intensity required to reach half-maximum activation of the three enzymes was similar (300-400 microEinsteins per square meter per second), while the light intensity required for half-maximum rates of photosynthesis was about 550 microEinsteins per square meter per second. The light activated levels of NADP-MDH and FBPase were well in excess of the in vivo activities which would be required during photosynthesis, while maximum activities of pyruvate,Pi dikinase were generally just sufficient to accommodate photosynthesis, suggesting the latter may be a rate limiting enzyme.

There was a large (5-fold) light activation of FBPase in isolated bundle sheath strands of maize, whereas there was little light activation of the enzyme in isolated mesophyll protoplasts. In mesophyll protoplasts the enzyme was largely located in the cytoplasm, although there was a low amount of light-activated enzyme in the mesophyll chloroplasts. The results suggest the chloroplastic FBPase in maize is primarily located in the bundle sheath cells.

     

Photosynthetic performance along a light gradient as related to leaf characteristics of a naturally occurring <Emphasis Type="Italic">Cypripedium flavum</Emphasis>

Photosynthesis, leaf structure, nitrogen content and nitrogen allocation in photosynthetic functions of Cypripedium flavum were studied in a naturally varying light regime. Light-saturated leaf net photosynthetic rate (A (max)) was strongly correlated with leaf dry mass per area (LMA), mesophyll conductance (g (m)) and area-based leaf nitrogen content (N(area)), with all variables increasing with increasing irradiance. Such coordinate variation of all these parameters illustrates the plastic response of leaf structure to high light (HL). Leaf N(area) was greater under HL than in low light (LL). The fractions of leaf nitrogen partitioning in carboxylation (P (R)) and bioenergetics (P (B)) were positively related to LMA. In contrast, P (R) and P (B) decreased with increasing mass-based leaf nitrogen content (N(mass)). However, no correlation was found between leaf nitrogen investment in light harvesting (P (L)) and either LMA or N(mass). Like maximum rate of carboxylation (V (cmax)) and electron transport (J (max)), the J (max)/V (cmax) ratio, which was strongly correlated to LMA, also increased significantly with irradiance. Under HL, leaf maximum photosynthetic nitrogen efficiency (ANUE) and intrinsic water use efficiency (WUE) were greater than in LL conditions, despite a small difference in WUE. This suggests that a functional balance in the photosynthetic machinery favors leaf photosynthetic plasticity of C. flavum in response to different light conditions. Given an ample soil nitrogen supply, C. flavum may offset its susceptibility to HL by efficient nitrogen use and higher stomatal and mesophyll conductance against photoinhibition so as to keep leaf photosynthesis positive.     

Effects of day and night temperature and temperature variation on photosynthetic characteristics

Net photosynthetic rates and mesophyll conductances were measured under standardized conditions for leaves of two C₃ and one C₄ annual species grown at temperatures of 20 to 32°C. Plants were grown with varying day and night temperatures, and also at constant temperatures equal to all the day and night temperatures used. Plants were grown with 8, 12, and 16 hours of light per day. This design allowed determination of whether photosynthetic characteristics were best correlated with day, night, mean, or time-weighted mean temperatures, The results showed that for Glycine max (L.) Merr. (C₃) night temperature was most important in determining photosynthetic characteristics, while in Helianthus annuus L. (C₃) and Amaranthus hypochondriacus L. (C₄) the time-weighted mean temperature was most important. The results for all species were consistent with the hypothesis that development of photosynthetic characteristics is related to a balance between the rate of leaf expansion and the rate of photosynthesis under the growth conditions.     

Effects of polyploidy on photosynthesis

In polyploid plants the photosynthetic rate per cell is correlated with the amount of DNA per cell. The photosynthetic rate per unit leaf area is the product of the rate per cell times the number of photosynthetic cells per unit area. Therefore, the photosynthetic rate per unit leaf area will increase if there is a less than proportional increase in cell volume at higher ploidal levels, or if cell packing is altered to allow more cells per unit leaf area. In autopolyploids (Medicago sativa, C₃ species, and Pennisetum americanum, C₄ species) there is a doubling of photosynthesis per cell and of cell volume in the tetraploid compared to the diploid. However, there is a proportional decrease in number of cells per unit leaf area with this increase in ploidy such that the rate of photosynthesis per leaf area does not change. There is more diversity in the relationship between ploidal level (gene dosage) and photosynthetic rates per unit leaf area in allopolyploids. This is likely to reflect the effects of natural selection on leaf anatomy, and novel genetic interactions from contributed genomes which can occur with allopolyploidy. In allopolyploid wheat (C₃ species) a higher cell volume per unit DNA at the higher ploidal level is negatively correlated with photosynthesis rate per unit leaf area. Although photosynthesis per cell increases with ploidy, photosynthesis per leaf area decreases, being lowest in the allohexaploid, cultivated bread wheat (Triticum aestivum). Alternatively, doubling of photosynthetic rate per cell with doubling of DNA, with apparent natural selection for decreased cell volume per unit DNA, results in higher rates of photosynthesis per leaf area in octaploid compared to tetraploid Panicum virgatum (C₄) which may be a case of allopolyploidy. Similar responses probably occur in Festuca arundinacea. Therefore, in some systems anatomical factors affecting photosynthesis are also affected by ploidal level. It is important to evaluate that component as well as determining the effect on biochemical processes. Current information on polyploidy and photosynthesis in several species is discussed with respect to anatomy, biochemistry and bases for expressing photosynthetic rates.Abbreviations Chl chlorophyll - RuBPC ribulose-1,5-bisphosphate carboxylase     

不同光照强度对西洋参光合特性,营养成分和产量的影响

在２１．６％自然光强下生长的西洋参叶片,光合作用的光饱和点和光补偿点皆比１１％自然光强下的高．在恒定条件下,光合作用最适温度为２８℃．２１．６％自然光强下的光合产物,较多地分配到根部,１１％自然光强下则分配到果实中的高．光合速率在一定范围内随透光强度的增加而提高,以透光３０％的叶片为最高．其日变化呈双峰曲线．叶绿素含量在一定范围内随光强的增加而降低,叶绿素ｂ含量的变化亦为同样趋势．叶片结构以弱光和强光相比,在上表皮角质层花纹、下表皮气孔数、叶肉细胞形状、叶绿体数及其基粒片层结构都有明显差别．参的产量随光强的增加而显著增加,但以透光３０％时增长幅度最大,４０％时增长变小．根中总皂苷和氨基酸含量在一定范围内随光强而增加,至透光４０％时又下降．     

Study on Leaf Anatomy and Photosynthesis of Cymbidium sinense

The leaf surface of Cymbidium sinense(Andr.) Willd was covered with cuticle and wax. The stomata were distributed in the dorsum of the leaf, the density being 100–130 mm-2 There was a stomatal cover on each stoma. The mesophyll was not differentiated into spongy tissue and palisade tissue. No chloroplast was observed in the vascular bundle sheath cells. The chloroplast in the mesophyll cells had well developed grana, with lightly stacked thylakoids and osmiophilic granules. The highest quantum yield of functional leaf was 0.082. The light compensation point of photosynthesis was about 5 μE·m-2·s-1, the light saturation point was about 200 μE·m-2·s-1. The photosynthetic ra,e of Cymbidium sinense was very low, generally 2.0–2.6 μmol CO2· m-2·s-1. The optimum temperature of photosynthesis of one-year-old leaf was 25℃. The photosynthe,ic rate of the three-year-old leaf declined with temperature rise. The ratio of chlorophyll a/b was about 2.7. The CO2 compensation point of photosynthesis was 105–220 ppm. All these data show that Cymbidium sinense belongs to the typical shade plants with low photosynthetic rate and high CO2 compensation point that explains that the growth of Cymbidium sinense is slow in nature.     

A model of dynamics of leaves and nitrogen in a plant canopy: an integration of canopy photosynthesis,leaf life span,and nitrogen use efficiency

A model of dynamics of leaves and nitrogen is developed to predict the effect of environmental and ecophysiological factors on the structure and photosynthesis of a plant canopy. In the model, leaf area in the canopy increases by the production of new leaves, which is proportional to the canopy photosynthetic rate, with canopy nitrogen increasing with uptake of nitrogen from soil. Then the optimal leaf area index (LAI; leaf area per ground area) that maximizes canopy photosynthesis is calculated. If leaf area is produced in excess, old leaves are eliminated with their nitrogen as dead leaves. Consequently, a new canopy having an optimal LAI and an optimal amount of nitrogen is obtained. Repeating these processes gives canopy growth. The model provides predictions of optimal LAI, canopy photosynthetic rates, leaf life span, nitrogen use efficiency, and also the responses of these factors to changes in nitrogen and light availability. Canopies are predicted to have a larger LAI and a higher canopy photosynthetic rate at a steady state under higher nutrient and/or light availabilities. Effects of species characteristics, such as photosynthetic nitrogen use efficiency and leaf mass per area, are also evaluated. The model predicts many empirically observed patterns for ecophysiological traits across species.