Estimating Ecosystem Maximum Light Use Efficiency Based On The Water Use Efficiency Principle

Light use efficiency (LUE) defines the vegetation efficiency of converting radiative energy into biochemical energy through photosynthesis. Estimating the maximum LUE (epsilon (max)) is critical yet challenging for quantifying gross primary production (GPP) using LUE-based models. This study describes an analytical method for estimating epsilon (max) based on water use efficiency (WUE) as determined by plant water use and carbon gain. Unlike other complex parameterization schemes, this WUE-based method is simple and requires four variables relatively easy to acquire. The WUE-based epsilon (max) estimates compare favorably well with values based on traditional curve fitting method and that reported in the literature, and clearly distinguished epsilon (max) between C-3 (1.48 +/- 0.33 g C MJ-1 PAR) and C-4 (2.63 +/- 0.21 g C MJ-1 PAR) dominated ecosystems. The range in epsilon (max) estimates was narrow across different years and sites within a biome. The WUE-based epsilon (max) estimate is theoretically constrained by vegetation water use and can be directly incorporated into LUE models for GPP estimation across ecosystems.