Abstract
According to the light-use efficiency model, differential biomass production among willow varieties may be attributed either to differences in the amount of light intercepted, the efficiency with which the intercepted light is converted to aboveground biomass, or both. In this study, variation in aboveground biomass production (AGBP) was analyzed in relation to fraction of incoming radiation intercepted (IPAR(F)) and light-use efficiency (LUE) for five willow varieties. The plants were grown in a short-rotation woody crop (SRWC) system and were in their first year of regrowth on a 5 year old root system. The study was conducted during a two-month period (June 15th-August 15th, 2001) when growing conditions were deemed most favorable. The objectives were: (1) to assess the relative importance of IPAR(F) in explaining variation in AGBP, and (2) to identify the key drivers of variation in LUE from a suite of measured leaf and canopy-level traits. Aboveground biomass production varied nearly three-fold among genotypes (3.55-10.02 Mg ha(-1)), while LUE spanned a two-fold range (1.21-2.52 g MJ(-1)). At peak leaf area index (LAI), IPAR(F) ranged from 66%-92%. Nonetheless, both IPAR(F) and LUE contributed to AGBP. An additive model combining photosynthesis on leaf area basis (A(area)), leaf mass per unit area (LMA), and light extinction coefficient (k) produced the most compelling predictors of LUE. In a post-coppice willow crop, the ability to maximize IPAR(F) and LUE early in the growing season is advantageous for maximizing biomass production.