Long-term elevated atmospheric CO2 and warming affect the root-associated microbiomes of rice and wheat

Abstract Background: Plant root-associated microbial communities profoundly affect plant nutrition and productivity. Although elevated atmospheric CO2 and warming have been suggested to affect above- and belowground plant processes, it remains unclear how root-associated microbial communities respond to elevated CO2 and warming, particularly in agroecosystems. Result: Here, an open-air field experiment was conducted to assay the interactive effects of elevated CO2 (500 ppm) and warming (+2℃) on the root-associated microbiomes and soil enzyme activities in a rice-wheat rotation ecosystem. The results revealed a significant increase in rhizosphere soil organic carbon (SOC) and total nitrogen contents from elevated CO2. In addition, glucosidase, β-xylosidase, and phosphatase activities increased significantly. The rhizosphere soils of rice and wheat had significantly higher richness and Shannon diversity indices than the root endosphere. Besides, the bacterial and fungal compositions were significantly altered between the two compartments. Elevated CO2 and warming had more impact on the rhizosphere soil microbiomes and altered their composition by changing the relative abundance of some particular groups. Soil pH, SOC, and available potassium significantly altered the dominant bacterial phyla in the rhizosphere. In contrast, the SOC affected the root endophytic bacterial phyla. Moreover, more bacterial and fungal genera were significantly correlated with soil variables in the rhizosphere than in the root endosphere. Elevated CO2 had significant effects on the numbers of bacterial genera, including Burkholderia, Rhizobium, Pantoea, Gemmatimonas, Dongia, Defluviicoccus, Anaeromyxobacter, and Povalibacter, that significantly correlated with soil variables. Conclusion: These results indicate that the microbial communities in the rhizosphere of rice and wheat are more sensitive to elevated CO2 and warming than the root endophytic microbiomes. Moreover, the dissimilarity of root-associated bacteria is greater than that of the fungal community in the root endosphere.