Temperature sensitivity of microbial respiration of paddy soils amended with rice residues produced under elevated CO2 and warming

Rice (Oryza sativa L.) residues (root and straw) are unique substrates for microbes in paddy soils. Microbial respiration (R-H) of paddy soils is likely to be affected by substrate quality. However, no relevant study on the effects of changed rice residue chemistry by climate change on the temperature sensitivity (Q(10)) of the R-H of soils amended with the residues is available. To fill this knowledge gap, we conducted an incubation experiment (at 15, 25, and 35 C-degrees) with rice residues of which lignin, nonstructural carbohydrate (NSC), and carbon-to-nitrogen ratio (C/N) were modified by growing the rice plants under different CO2 and air temperature (T-air). Co-elevated CO2 and T-air decreased lignin and C/N but increased the NSC contents of the residues, leading to the greater R-H in the soils amended with rice residues produced under co-elevated CO2 and T-air compared to other CO2 or T-air treatments. However, the Q(10) values of the R-H of soils amended with rice residues produced under different CO2 and T-air were marginally changed, probably due to other confounding factors such as soil enzyme activity and nutrient availability. Despite that, there was a negative relationship between NSC and Q(10) for soils amended with straw of which C/N is lower than root, agreeing with the kinetic theory on "substrate quality-Q(10) relationship". Our result suggests that residue chemistry may not affect the Q(10) of soils with root residue, but for straw-amended soils, less-recalcitrant NSC rather than more-recalcitrant lignin of straw may be critical in determining the Q(10) of the soils.