The global contribution of roots to total soil respiration

Abstract Aim Soil respiration ( R S ) is one of the largest fluxes in the global carbon cycle. It is composed of respiration by roots and heterotrophic organisms, with each component having distinctive drivers and sensitivities and, consequently, varying feedback potential to climate change. Global drivers of the total flux of R S are widely studied and generally accepted, but our understanding of the factors governing its component fluxes lags far behind. Location Global. Time period 1962–2015. Major taxa studied Plant roots and soil microbes. Methods Combining a newly updated global database of R S partitioning measurements with biotic and abiotic variables, we examined the world‐wide distribution of the proportion of the annual root respiration ( R root ) contribution to R S ( R root : R S ). We investigated how R root : R S varies by ecosystem type, measurement method and climate. We used a random forest model to predict the relationship between field measurements of R root : R S ( n = 880) and 14 biotic and abiotic factors, including climate, nitrogen deposition, soil, mycorrhiza, biomass and satellite‐derived greenness. Finally, we present a global map of predicted R root : R S at 0.5° resolution. Results Consistent with previous studies, we found no clear trends of mean R root : R S across ecosystem types and measurement methods. The area‐weighted overall mean of predicted R root : R S was .42 ( SD ± .18; i.e., 42% of total global R S was generated by plant roots). Predicted R root : R S and related environmental factors did exhibit clear spatial patterns between climatic regions, with higher R root : R S in dry and cold regions and lower R root : R S in temperate and tropical regions. Main conclusions Given that R root : R S is linked to plant carbon use efficiency (CUE, the ratio of net primary production to gross primary production), but generated from measurements completely independent of plant CUE, it might provide crucial insights into ecosystem‐ to global‐scale carbon cycling. This study thus provides a framework to explore global carbon allocation under global climate change.