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 delta C-13 technique. Roots of rice grown with elevated [CO2] were significantly depleted in C-13 by more than 6 parts per thousand compared to those with ambient [CO2], leading to a low delta C-13 of SOC via rhizodeposition of C-13-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 (T-air) conditions, respectively. The greater roots-derived C under elevated T-air than that under ambient T-air collaborated with increased root biomass by elevated T-air. However, SOC balance analysis revealed that 0.16 and 0.21 kg m(-2) of autochthonous SOCs were decomposed under ambient and elevated T-air, respectively, during the growth season. Therefore, elevated T-air 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.