Foliar morphology and canopy nitrogen as predictors of light-use efficiency in terrestrial vegetation

The net primary productivity (NPP) of a plant community is often positively and linearly related to the amount of photosynthetically active radiation absorbed by its canopy (APAR). The slope of this relationship is governed by the efficiency (ε) of APAR use in biomass production (NPP = APAR×ε). This intuitive model offers a promising means of generating large-scale NPP estimates, but its utility is compromised by our inability to explain considerable differences in ε across species, functional groups, and environments. Using data from the literature, we examined the possibility that variation in ε was governed largely by two chemical and morphological characteristics of the vegetation, canopy nitrogen content (Ncanopy) and the canopy average for leaf mass per unit area (Marea). Specifically, we hypothesized that ε was positively related to the quotient of Ncanopy (adjusted for the fraction of incident PAR absorbed by the canopy, fPAR) and Marea. This ε index accounts for the dependence of light utilization on the quantity of photosynthetic “machinery” (Ncanopy) and its inherent efficiency, which is inversely related to Marea. Across a wide array of C3 species, functional groups and environments, ε (based on aboveground NPP) was strongly and positively related to [Ncanopy/fPAR]/Marea (r2 = 0.85, P < 0.0001). Adoption of the index as a basis for estimating ε could improve APAR-based predictions of terrestrial NPP, agricultural crop yield and vegetation responses to global change. © 2002 Elsevier Science B.V. All rights reserved.