Global Spectrum of Vegetation Light‐Use Efficiency

Vegetation light‐use efficiency (LUE) is a critical parameter of vegetation photosynthesis, but its global variations and the drivers remain poorly understood. Here, we used data from 172 flux tower sites to characterize the global distribution of ecosystem‐level LUE spanning various vegetation and climate. The global growing season average LUE was 1.30 ± 0.55 g C MJ−1 for 2000–2014. The main factors driving LUE variations included environmental conditions (e.g., temperature), plant traits (e.g., foliar nitrogen concentration and isohydricity) and their interactions, which together accounted for about 76% of the observed global variations in LUE. However, an ensemble of 11 dynamic global vegetation models largely underestimated LUE, and hardly captured the key drivers. Our results highlight that a paradigm shift from vegetation functional type‐based scheme to trait‐climate spectrum‐based scheme is necessary for the next‐generation models to accurately simulate the response of vegetation carbon uptake to climate change. Plain Language Summary Vegetation light‐use efficiency (LUE) is a key factor for reliable estimations of gross primary production, which is an important component of terrestrial carbon cycle. Thorough knowledge of global vegetation LUE and the drivers is required for better understanding the response of terrestrial ecosystems to climate change. Using measurements from 172 flux tower sites and satellite observations, we found large spatial variations in LUE globally. These large variations were primarily driven by environmental factors, plant functional traits and their interactions. However, dynamic global vegetation models strongly underestimated LUE over most sites globally, and could not represent the response of LUE to main drivers, suggesting the potential model improvements through incorporating the trait‐based approaches. Our findings address the urgency of accounting for the synergism of plant traits and their interactions with environmental factors for better diagnosing and predicting the response of vegetation photosynthesis to climate change. Key Points Global growing season average vegetation light‐use efficiency (LUE) is 1.30 ± 0.55 g C MJ−1 during the period of 2000–2014 Environmental conditions, plant traits and their interactions synergistically determine global LUE variations Dynamic global vegetation models largely underestimate LUE, and hardly capture its response to key drivers