Global patterns of rhizosphere effects on soil carbon and nitrogen biogeochemical processes

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The rhizosphere controls soil carbon (C) and nitrogen (N) cycling via rhizodeposition. However, rhizosphere effects on soil C mineralization (Cmin) and net N mineralization (Nmin) rates have rarely been quantified at the global scale. We performed a meta-analysis of 1875 pairwise observations from 155 articles to assess rhizosphere effects on soil Cmin and net Nmin at the global scale. The results showed that rhizosphere effects significantly enhanced soil Cmin and net Nmin by 25.43 and 26.77%, respectively, and these rhizosphere effects were higher in humid regions than in arid regions and higher under woody plants than under herbaceous plants. The rhizosphere effects on soil Cmin and net Nmin were significantly correlated with latitude, mean annual precipitation, soil organic carbon (only for net Nmin), available N and microbial biomass carbon. We conclude that geographical characteristics and bulk soil properties were most important in determining rhizosphere effects on soil biogeochemical processes, although plant life forms also showed significant effects. These results support the microbial activation hypothesis and N mining hypothesis, demonstrate the coupled nature of soil C and N cycling in the rhizosphere, and indicate the importance of rhizosphere effects for turning over soil organic matter and increasing nutrient concentrations. Overall, the results from this meta-analysis provide novel insights into rhizosphere effects on soil Cmin and net Nmin among precipitation regions and plant life forms, which can contribute to the prediction of how rhizosphere regulate soil C and N biogeochemical cycling in terrestrial ecosystems at large scales.