Plant-mediated effects of elevated CO₂ and rice cultivars on soil carbon dynamics in a paddy soil

Soil organic carbon (SOC) sequestration under elevated CO₂ concentration (eCO₂ ) is a function of carbon (C) input and C retention. Nitrogen (N) limitation in natural ecosystems can constrain plant responses to eCO₂ and their subsequent effects on SOC, but the effect of eCO₂ on SOC in N-enriched agroecosystems with cultivars highly responsive to eCO₂ is largely unknown. We reported results of SOC dynamics from a field free-air CO₂ enrichment experiment with two rice cultivars having distinct photosynthetic capacities under eCO₂ . A reciprocal incubation experiment was further conducted to disentangle the effect of changes in litter quality and soil microbial community on litter-derived C dynamics. eCO₂ significantly increased total SOC content, dissolved organic C and particulate organic C under the strongly responsive cultivar, likely due to enhanced organic C inputs originated from CO₂ stimulation of shoot and root biomass. Increases in the residue C : N ratio and fungal abundance induced by eCO₂ under the strongly responsive cultivar reduced C losses from decomposition, possibly through increasing microbial C use efficiency. Our findings suggest that applications of high-yielding cultivars may substantially enhance soil C sequestration in rice paddies under future CO₂ scenarios.