Global patterns of plant carbon use efficiency and their climate drivers deduced from MODIS satellite data and process-based models

Defined as the ratio between net primary production (NPP) and gross primary production (GPP), carbon use efficiency (CUE) represents the capacity of plants to assimilate carbon from the atmosphere. Although carbon-cycle models could provide GPP and NPP outputs, yet the performance of their ratio has not been fully researched. In this study, we investigated the spatial patterns of plant CUE deduced from a MODIS satellite data and five carbon-cycle models, and then analyzed the responses of CUE to climate drivers. Results show that process models give an average CUE of 0.45±0.05 (range from 0.35 to 0.52), slightly lower than the value of 0.49 obtained from MODIS data. The different datasets broadly agree on the spatial variation of CUE, including a strong latitudinal gradient, with greater CUE at high latitudes. However, there are still some discrepancies; these mainly occur in temperate regions, and can largely be attributed to systematic differences in autotrophic respiration. In both the satellite-based dataset and process models, plant CUE declines non-linearly with increase in temperature, while the trend is relatively stable with enhanced precipitation, indicating that plant CUE appears to be mainly controlled by mean annual temperature rather than mean annual precipitation. Our findings suggest an urgent need to refine the simulations to better account for global patterns of CUE by improving the representation of processes that are not yet accurately simulated in current datasets and incorporating other missing processes.