Sequestration of roots-derived carbon in paddy soil under elevated CO2 with two temperature regimes as assessed by isotope technique

Paddy soils are considered to have a great soil organic carbon (SOC) sequestration potential. The present study was conducted to estimate the amount of new C derived from rice-roots in a paddy soil under global warming with elevated CO2 concentration ([CO2]) using δ13C technique. Roots of rice grown with elevated [CO2] were significantly depleted in 13C by more than 6% compared to those with ambient [CO2], leading to a low δ13C of SOC via rhizodeposition of 13C-depleted C under elevated [CO2]. The net C storage derived from roots was estimated to be 0.25 and 0.31 kg m-2 under ambient and elevated air temperature (Tair) conditions, respectively. The greater roots-derived C under elevated Tair than that under ambient Tair collaborated with increased root biomass by elevated Tair. However, SOC balance analysis revealed that 0.16 and 0.21 kg m-2 of autochthonous SOCs were decomposed under ambient and elevated Tair, respectively, during the growth season. Therefore, elevated Tair may enhance incorporation of new C derived from roots to SOC pool due to increased belowground biomass, but warming may also increase decomposition of old SOC by stimulating temperature-sensitive microbial activities.