Effects of elevated CO₂ and warming on the root-associated microbiota in an agricultural ecosystem

Plant root-associated microbial communities profoundly affect plant nutrition and productivity. Although elevated atmospheric CO₂ and warming affect above- and belowground plant processes, it remains unclear how root-associated microbial communities respond to elevated CO₂ and warming. In this study, an open-air field experiment was conducted to assay the interactive effects of elevated CO₂ (500 ppm) and warming (+2°C) on the root-associated microbiota and soil enzyme activities in a rice-wheat rotation ecosystem. The results revealed that elevated CO₂ significantly increased rhizosphere soil organic carbon (SOC) and total nitrogen contents. In addition, glucosidase, β-xylosidase, and phosphatase activities significantly increased. The richness and Shannon diversity indices were significantly higher in rhizosphere soil than in root endosphere. Elevated CO₂ and warming significantly impacted the rhizosphere soil microbiota and altered their composition by changing the relative abundance of some specific groups. Soil pH, SOC, and available potassium content significantly altered the dominant bacterial phyla in the rhizosphere. SOC affected root endophytic bacterial phyla. Bacterial and fungal genera were significantly correlated with soil variables in the rhizosphere than in the root endosphere. These results indicate that microbial communities in the rhizosphere are more sensitive to elevated CO₂ and warming than those in the root endosphere.