Belowground interplant carbon transfer promotes soil carbon gains in diverse plant communities

Diverse plant communities are known to increase soil carbon (C) levels compared to monocultures, but an incomplete understanding of the underlying mechanisms of this phenomenon limits the development of strategies for optimizing soil C sequestration. Here, we hypothesized that the identity of neighboring plants influences the amounts of C that a plant inputs into the soil, the resultant formation of soil pore architecture, and the fate of the plant's C inputs. To test this hypothesis, we combined ¹³CO₂ plant pulse labeling with X-ray computed micro-tomography (μCT) in assessing plant-assimilated C from three species common to North American prairie: switchgrass, big bluestem, and wild bergamot. The plants were grown in a greenhouse in monoculture and in all-pair combinations. The ¹³C labeling was conducted so as to ensure that only one member of each pair has received ¹³C. The results demonstrated that greater belowground C exchange among neighboring plants enhanced inputs of plant-assimilated C into soil, suggesting that the involvement of plant community members in belowground C transfer, rather than community's diversity per se, drives rapid soil C accrual. Moreover, the magnitudes of C losses as well as properties of soil pore architecture also depend not only on the identity of the C source plant itself but also on the identities of its neighbors. These findings propose belowground interspecific C transfer as a previously overlooked mechanism for enriching and stabilizing soil C and suggest genomic and management potentials for selecting species that participate in intensive interspecific assimilate exchange in order to promote rapid and stable soil C gains.