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Abstract The observation of acclimation in leaf photosynthetic capacity to differences in growth irradiance has been widely used as support for a hypothesis that enables a simplification of some soil-vegetation-atmosphere transfer (SVAT) photosynthesis models. The acclimation hypothesis requires that relative leaf nitrogen concentration declines with relative irradiance from the top of a canopy to the bottom, in 1 : 1 proportion. In combination with a light transmission model it enables a simple estimate of the vertical profile in leaf nitrogen concentration (which is assumed to determine maximum carboxylation capacity), and in combination with estimates of the fraction of absorbed radiation it also leads to simple ‘big-leaf’ analytical solutions for canopy photosynthesis. We tested how forests deviate from this condition in five tree canopies, including four broadleaf stands, and one needle-leaf stand: a mixed-species tropical rain forest, oak (Quercus petraea (Matt.) Liebl), birch (Betula pendula Roth), beech (Fagus sylvatica L.) and Sitka spruce (Picea sitchensis (Bong.) Carr). Each canopy was studied when fully developed (mid-to-late summer for temperate stands). Irradiance (Q , µ mol m-2 s-1 ) was measured for 20 d using quantum sensors placed throughout the vertical canopy profile. Measurements were made to obtain parameters from leaves adjacent to the radiation sensors: maximum carboxylation and electron transfer capacity (V a , J a , µ mol m-2 s-1 ), day respiration (R da , µ mol m-2 s-1 ), leaf nitrogen concentration (N m , mg g-1 ) and leaf mass per unit area (L a , g m-2 ). Relative to upper-canopy values, V a declined linearly in 1 : 1 proportion with N a . Relative V a also declined linearly with relative Q , but with a significant intercept at... [ABSTRACT FROM AUTHOR]

Analyzes the effect of elevated carbon dioxide concentration on photosynthesis in European forest species using meta-analysis techniques. Relationship between the down-regulation of photosynthesis and poor nutrient status or accumulation of starch; Induction of nutrient limitation by carbon availability.