Covariation between gross primary production and ecosystem respiration across space and the underlying mechanisms: A global synthesis

Gross primary production (GPP) and ecosystem respiration (RE) are two important processes in the terrestrial carbon cycle. Understanding the relationships between GPP and RE across space, as well as the underlying mechanisms, is helpful for understanding the terrestrial carbon cycle and predicting the global carbon budget. In this study, we investigated the correlation between the spatial variations in GPP and RE by compiling carbon flux data from 264 sites across the Asian, European, North American, South American, African, and Oceanian regions. The results indicated that GPP and RE covaried across space regionally and globally (P < 0.001). The spatial variations in GPP explained 66-98% of the variations in RE in the six regions (approximately explained 60-76% when considered the effects of self-correlation caused by current flux partitioning algorithm), and it explained 90% of RE variations at the global scale (about 70% when considered the effects of self-correlation). RE/GPP values were not significantly different among the six regions or between the two hemispheres. RE/GPP values consistently averaged at 0.87 ± 0.04 along the spatial variations in climate and vegetation index. This covariation between GPP and RE across space is largely attributed to the parallel responses of GPP and RE to the common climatic and vegetation factors, but the underlying mechanism lies in productivity as the primary and direct substrate supplier for respiration which fundamentally constrains RE. These results suggest that the variation in photosynthate availability is the dominant driver for respiration across space and that this process must be fully considered in the cross-site RE comparisons.