Rhizodeposition stimulates soil carbon decomposition and promotes formation of mineral-associated carbon with increased clay content

Rhizodeposition plays a key role in the formation and decomposition of soil organic carbon (SOC), but interactions with clay remain unclear. In this study, we examined how rhizodeposition contributes to SOC decomposition and the formation of particulate and mineral-associated organic C (POC and MAOC, respectively) in different soils with varying clay content. We collected soils from a grassland site covering three soil types and two depths, ranging in clay content from 15.6 to 66.4 %. We then grew ryegrass (Lolium perenne) in these soils in a glasshouse. After 76 days, plants were pulse-labelled with 13C-enriched CO2 to assess rhizodeposit C and SOC decomposition rates and the recovery of rhizodeposition in microbial biomass, POC and MAOC. The SOC decomposition showed no relationship with clay content, but a strong positive relationship with rhizodeposit C decomposition, indicating a positive rhizosphere priming effect. The rhizodeposition recovered in the MAOC was positively related to clay content and rhizodeposition recovered in microbial biomass. Our results suggest that microbial products from rhizodeposition are increasingly incorporated into MAOC with increased clay content. Our results further highlight the role of rhizodeposition for soil C decomposition and stabilisation and how both processes interact with clay content.