Differential responses of soil bacterial communities to elevated CO2 between strongly CO2-responsive and weakly CO2-responsive rice cultivars

Effects of elevated CO2 (eCO2) on paddy soil microbial communities remain unclear, particularly when different rice cultivars exposed to eCO2. We thus compared responses of soil bacterial communities to ambient CO2 (aCO2) and eCO2 (aCO2 + 200 μmol CO2 mol-1) between two weakly CO2-responsive (Wuyunjing27, W27; Huaidao5, H5) and two strongly CO2-responsive rice cultivars (Yongyou1540, Y1540; LongIIyou1988, L1988) throughout six growth stages (early tillering, late tillering, jointing, heading, grain filling and ripening) in a paddy field in Jiangdu, China in 2018. No significant changes in soil bacterial diversities were observed between eCO2 and aCO2 or between cultivars for any single growth stage at the OTU level, but α diversity significantly changed at the phylum level except for the ripening stage. For a single cultivar, particularly two strongly CO2-responsive cultivars, over their whole growth stage, eCO2 enhanced differences in bacterial β diversity at both OTU and phylum levels under H5, Y1540 and L1988. Soil bacterial community complexity at the phylum level under eCO2 was weakened under W27, H5 and Y1540, but enhanced under L1988. eCO2-induced changes in soil DOC under these four cultivars had significantly positive impact on bacterial abundances. However, structural equation modeling illustrated that changes in soil DOC induced by eCO2 significantly decreased soil bacterial community richness. eCO2 did not significantly affect relationships between soil bacterial community diversities and rice yields, but displayed significantly negative correlations between strongly CO2-responsive rice cultivars' yields and relative abundances of Proteobacteria at the ripening stage. Dynamics that how soil microbial communities can differentiate their eCO2 responses between strongly- and weakly-responsive rice cultivars will provide a new insight into promoting rice productivity and soil health.