Global Patterns and Climate Controls of Terrestrial Ecosystem Light Use Efficiency

Defined as the ratio of gross primary productivity (GPP) and the absorbed photosynthetically active radiation (APAR), light use efficiency (LUE) is a critical parameter describing the ability of vegetation to convert the energy in absorbed light to photosynthesis carbon uptake. However, the spatial patterns and climate drivers of LUE at global scale still remain poorly documented, resulting in large uncertainty in the estimation of global photosynthetic productivity and its relationship with climate. In this study, we investigate the global patterns and climate controls of annual mean LUE with data-driven estimates of global LUE and ten carbon cycle models. Global annual mean LUE estimated from data-driven model is 0.87±0.25 gC MJ^-1, slightly higher than mean of the simulations from ten process-based models (process model hereafter), which is 0.73±0.22 gC MJ^-1. In both data-driven model and process model, LUE varies greatly with latitudes and vegetation types. Evergreen broad forests have the highest LUE while closed shrublands have the lowest LUE. However, process model estimates lower LUE in most biomes compared with data-driven model. Spatially, LUE from data-driven model shows the highest LUE in western Europe, followed by tropical regions as well as southeastern North America, and high latitude regions have the lowest LUE, while LUE from process model is highest in tropical regions, followed by eastern Siberia. For process model, LUE over 70% of the vegetation land is controlled by precipitation, which is higher than data-driven model (about 61%). Further analyses find the sensitivities of LUE to temperature and solar radiation in process model gradually change from negative to positive as the precipitation increases, indicating the significant response of LUE to the interaction of precipitation and temperature/solar radiation. This study provides a better understanding of global pattern and climate control of LUE, highlighting the importance of interactions of climatic factors in regulating response of photosynthesis to climate change.