An antagonistic effect of elevated CO2 and warming on soil N2O emissions related to nitrifier and denitrifier communities in a Chinese wheat field

Aims Although elevated atmospheric CO2 and global warming are important climate factors that affect soil carbon sequestration and greenhouse gases emission from agricultural soils, it remains unclear how these factors affect the soil microbial communities that involved in nitrous oxide (N2O) emission. The objectives of this study were to evaluate the interactive effects of elevated CO2 and warming on soil microbial community and its relationship with soil N2O emission. Methods Soil N2O emission was monitored in a Free-Air CO2 Enrichment facility equipped with warming during wheat growth season. The abundance and community composition of ammonia-oxidizing bacteria (AOB) and archaea (AOA) and denitrifiers (nirK, nirS and nosZ) in the rhizosphere were determined using real-time PCR and Illumina MiSeq sequencing technique. Results Elevated CO2 increased N2O emission, the abundance of AOB and nirK, the concentration of rhizospheric soil organic carbon (SOC) and total nitrogen (TN); while it decreased the concentration of soil available phosphorus and potassium. Warming decreased soil pH, and the abundance of AOB, nirK and nosZ; and the effect of warming on soil N2O emission, SOC, TN and AOB abundance was significantly interacted with elevated CO2. Under elevated CO2, warming decreased soil N2O emission but increased the concentration of rhizosphere SOC and TN. Pyrosequencing showed that AOB, nirK, and nosZ community compositions were altered by elevated CO2 levels, and redundancy analyses further showed that variations in SOC, TN and pH determined these community compositions. Soil N2O emission was positively corelated with soil pH, the content of SOC and nitrate, and the abundance of AOB and nirK. Conclusions Our results demonstrated that future climate change of elevated CO2 plus warming will not lead to a significant increase in agricultural soil N2O emission. Ammonia oxidizer (AOB) and denitrifier (nirK) are the key soil microbial community that regulate the response of soil N2O emission to elevated CO2 and warming.