Agricultural and Forest Meteorology 115 (2003) 163–171 Foliar morphology and canopy nitrogen as predictors of light-use efficiency in terrestrial vegetation D. Scott Green a,∗ , John E. Erickson b , Eric L. Kruger b a Ecosystem Science and Management, University of Northern British Columbia, Prince George, BC, Canada V2N 4Z9 b Department of Forest Ecology and Management, University of Wisconsin, Madison, WI 53706, USA Received 22 April 2002; received in revised form 10 October 2002; accepted 17 October 2002 Abstract The net primary productivity (NPP) of a plant community is often positively and linearly related to the amount of photosyn- thetically 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, func- tional 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 (N canopy ) and the canopy average for leaf mass per unit area (M area ). Specifically, we hypothesized that ε was positively related to the quotient of N canopy (adjusted for the fraction of incident PAR absorbed by the canopy, f PAR ) and M area . This ε index accounts for the dependence of light utilization on the quantity of photosynthetic “machinery” (N canopy ) and its inherent efficiency, which is inversely related to M area . Across a wide array of C 3 species, functional groups and environments, ε (based on aboveground NPP) was strongly and positively related to [N canopy /f PAR ]/M area (r 2 = 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. Keywords: Light-use efficiency; Leaf nitrogen content; Leaf mass per area; Leaf area index; Net primary productivity 1. Introduction Vegetation requires light energy to convert atmos- pheric CO 2 into essential organic compounds required for plant growth and maintenance. Accordingly, plant biomass production by terrestrial vegetation has been observed to be strongly and positively related to the canopy absorption of photosynthetically active radi- ation (APAR; Monteith, 1972). The proportional re- lationship between net primary productivity (NPP) ∗ Corresponding author. Tel.: +1-250-960-5817; fax: +1-250-960-5539. E-mail address: greens@unbc.ca (D. Scott Green). and APAR, known as the light-use efficiency (LUE) or epsilon (ε) model, is commonly used to explain and/or predict NPP variation in agricultural and for- est ecosystems (Monteith, 1977; Jarvis and Leverenz, 1983; Ruimy et al., 1994; Runyon et al., 1994; Field et al., 1995; Gower et al., 1999; Sinclair and Muchow, 1999). It is also viewed as a potentially effective ap- proach for modeling the responses of NPP to global change (Field et al., 1995; Haxeltine and Prentice, 1996; Hui et al., 2001). The relationship between plant productivity and APAR is governed by ε (defined either as NPP/APAR or the slope of NPP vs. APAR), which integrates all photosynthetic and respiratory processes. The ε 0168-1923/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0168-1923(02)00210-1