Climate-driven global changes in carbon use efficiency

Aim: Carbon use efficiency [net primary production (NPP)/gross primary production (GPP) ratio] is a parameter related to the allocation of photosynthesized products by plants and is commonly used in many biogeochemical cycling models. But how this parameter changes with climates is still unknown. Faced by an aggravated global warming, there is a heightened necessity in unravelling the dependence of the NPP/GPP ratio on climates. The objective of this study was to examine how ongoing climate change is regulating global patterns of change in the NPP/GPP ratio. The study finding would elucidate whether the global vegetation ecosystem is becoming more or less efficient in terms of carbon storage under climatic fluctuation. Location: The global planetary ecosystem. Methods: The annual NPP/GPP ratio of the global terrestrial ecosystem was calculated over a 10-year period based on Moderate Resolution Imaging Spectroradiometer data and an ecosystem productivity model. The temporal dynamics of the global NPP/GPP ratio and their dependence on climate were investigated. Results: The global NPP/GPP ratio exhibited a decreasing trend from 2000 to 2009 due to decreasing NPP and stable GPP over this period. The temporal dynamics of the NPP/GPP ratio were strongly controlled by temperature and precipitation. Increased temperature lowered the NPP/GPP ratio, and increased precipitation led to a higher NPP/GPP ratio. Conclusions: The NPP/GPP ratio exhibits a clear temporal pattern associated with climatic fluctuations at a global scale. The associations of the NPP/GPP ratio with climatic variability challenge the conventional assumption that the NPP/GPP ratio should be consistent independent of environmental conditions. More importantly, the findings of this study have fundamental significance for our understanding of ongoing global climatic change. In regions and time periods experiencing drought or increased temperatures, plant ecosystems would suffer a higher ecosystem respiration cost and their net productivity would shrink.