Positive rhizospheric effects on soil carbon are primarily controlled by abiotic rather than biotic factors across global agroecosystems

The carbon (C) that surrounds the rhizosphere serves as the nexus between soil, plants, and atmosphere. Although it is known that rhizospheric C is sensitive to soil management and environmental changes, the influences of crop roots on rhizospheric C across global agroecosystems have not yet been systematically quantified, which limits our understanding of the terrestrial C cycle. A comprehensive meta-analysis including 748, 294, and 695 paired data of soil organic carbon (SOC), dissolved organic carbon (DOC), and soil microbial biomass carbon (SMBC) in rhizosphere and corresponding bulk soil from 154 papers, together with 25 biotic and abiotic variables, was conducted to quantify the effects of the rhizosphere on soil carbon across global agroecosystems. We found that the rhizosphere had greater SOC, DOC, and SMBC compared to the bulk soil, with 7.0%, 34.6%, and 26.1%, respectively. Rhizospheric effects on SOC and DOC varied significantly with different climate zones, aridity indices, and crop types; however, this phenomenon did not occur with SMBC. Soil available nutrients were the main driving factor behind rhizospheric SOC (relative influence of 37.0%), whereas SMBC played a small role in regulating the rhizosphere DOC, aside from the aridity index, crop type, initial soil C, and soil pH. The soil microbial structure, diversity, and function were not critical for regulating rhizospheric C. Path analysis revealed an intercorrelated network involving climate, physicochemical soil properties, and SMBC to determine the rhizospheric impacts on SOC and DOC. Understanding the size and driving factors of the rhizospheric effects on soil C is useful for determining how crop selection might affect broader C and nutrient cycling in agroecosystems.

Automated summary

This study conducted a comprehensive meta-analysis to quantify the effects of the rhizosphere on soil carbon across global agroecosystems. The results showed that the rhizosphere had significantly higher soil organic carbon, dissolved organic carbon, and soil microbial biomass carbon compared to the bulk soil. The effects of the rhizosphere on different carbon fractions varied with climate zones, aridity indices, and crop types.