Biomass, chemical composition, and microbial decomposability of rice root and straw produced under co-elevated CO2 and temperature

Rice residue including root and straw are unique carbon (C) source in paddy soils. However, the potential changes in quantity and chemical composition of rice residue under co-elevated atmospheric CO 2 concentration ([CO 2 ]) and air temperature (T air ) and the legacy effect of the changed chemical composition on residue decomposition have not been investigated. This study was conducted to investigate biomass, chemical composition, and decomposability of rice root and straw produced under elevated [CO 2 ] and T air . Root and straw biomass increased by elevated [CO 2 ] and elevated T air , respectively, and the greatest biomass was achieved under co-elevated [CO 2 ]-T air for both root and straw. The concentration of lignin (recalcitrant) decreased while that of nonstructural carbohydrates (less recalcitrant) increased by co-elevated [CO 2 ]-T air . The ratio of lignin-to-nitrogen (lignin/N) decreased by co-elevated [CO 2 ]-T air compared to ambient [CO 2 ]-T air due to increased N and decreased lignin concentrations. Decomposability of root (lignin/N, 36.4) produced under co-elevated [CO 2 ]-T air was greater than that under ambient co-elevated [CO 2 ]-T air (lignin/N, 53.7); however, there was no difference in decomposability for straw, which had relatively narrow range of lignin/N (27.3–36.5) regardless of [CO 2 ]-T air conditions. The results of this study provide a novel insight into the changes in quantity and quality of rice residue under elevated [CO 2 ]-T air that are necessary to predict changes in paddy soil C sequestration under global warming.