Effects of Elevated CO₂ on the Abundance of Rhizosphere Bacteria,Fungi and Denitrification Bacteria in Different Soybean Cultivars

The CO₂-induced rhizospheric microbes response is essential to soil carbon cycling. In order to investigate the interactive effects of elevated CO₂(eCO₂) and soybean cultivars on the abundance of rhizosphere microorganisms in Northeast China, we conducted an OTC (open top chamber) experiment using 4 soybean cultivars (i. e. Xiaohuangjin, Suinong 8 hao, Suinong 14 and Heinong 45) grown in a Mollisol under ambient CO₂ (390 ppm) and eCO₂ (550 ppm), respectively. Also, we used Real-time quantitative PCR targeting 16S rRNA, ITS and nirS genes in the experiment. The results showed that the copy numbers of 16S rRNA gene were significantly affected by elevated CO₂ (p=0.006) and soybean cultivars (p=0.013). The elevated CO₂ increased the abundance of bacteria regardless of soybean cultivars, while the interactive effects of elevated CO₂ and soybean cultivars on the abundance of bacteria were not significant. The elevated CO₂, soybean cultivars and their interactive effects on the fungal abundance were all significant (p<0.001), which indicated that fungi was more sensitive than bacteria to the elevated CO₂. On the other hand, the elevated CO₂ (p=0.169), soybean cultivars(p=0.404) and their interactive effects (p=0.059) on the copy numbers of denitrification bacterial nirS gene were all not significant.