Divergent contributions of living roots to turnover of different soil organic carbon pools and their links to plant traits

Abstract

Abstract Rhizodeposits and root litter contribute critically to soil organic carbon (SOC) formation and decomposition. This root‐induced SOC turnover shows great interspecific variations. Bulk SOC consists of diverse functional pools differing in formation and stabilization. Yet, it remains unclear which plant traits regulate the effects of living roots on the turnover of different SOC pools across species. By performing 13CO2 continuous labelling of six grassland species for a growing season in a climate‐controlled chamber, we quantified the contributions of living roots to the dynamics of the fast‐cycling particulate organic C and the slow‐cycling mineral‐associated organic C, and explored their relations to plant traits. The results showed that new root‐derived SOC varied more than threefold among the six species. The variation in new root‐derived SOC was best explained by the ratio of shoot to root biomass. Plant species with higher shoot:root ratio formed more new root‐derived SOC. Most of the root‐derived C (72%) was incorporated into the particulate organic C pool. All species caused positive rhizosphere priming effects (RPE), which varied sevenfold across species. Among plant traits, specific root length was the best predictor of interspecific variations in the RPE, with greater RPE associated with higher specific root length. Most of the RPE (70%) occurred in the mineral‐associated organic C pool. Our results also showed that most plant species caused more old SOC decomposition via the RPE than new SOC formation, leading to net SOC losses, especially for the mineral‐associated organic C pool. Overall, we provide novel insights into the effects of plant traits on root‐induced turnover of particulate and mineral‐associated organic C. Our findings should be valuable for understanding how specific plant traits regulate SOC accumulation and stabilization. A free Plain Language Summary can be found within the Supporting Information of this article.