Effects of elevated CO2 and O3 and N fertilization on amount of soil microbial biomass carbon in spring wheat growing season

Experimental platform of Open-top chambers (OTC) was established in 2006 over a spring wheat system, it located at the National Field Observation and Research Station of Shenyang Agro-ecosystems, a member of Chinese Ecosystem Research Network (CERN) established in 1987. We compared the dynamics of soil microbial biomass C with high (225.0 kg N hm(-2)) and low (150.0 kg N hm(-2)) application rate of chemical fertilizer N exposed to the elevated CO2, O-3, CO2 plus O-3 and CK after the spring wheat growing season in 2010. The results showed that under elevated CO2 concentration at the jointing stage, high application rate of chemical fertilizer N significantly declined the amount of soil microbial biomass C by 64.97%, compared with the low N application rate of chemical fertilizer N (p<0.01). In treatment with low application rate of chemical fertilizer N, elevated O-3 concentration significantly declined the amount of soil microbial biomass C by 52.49% (p<0.05), compared with CK. In treatment with high application rate of chemical fertilizer N, the interaction of CO2 and O-3 increased significantly the amount of soil microbial biomass C by 50.03 % (p<0.05), compared with CK. At the ripening stage, under elevated CO2 concentration and interaction of CO2 and O-3, high application rate of chemical fertilizer N significantly decreased the amount of soil microbial biomass C by 32.92% and 41.45%, compared with low N application rate of chemical fertilizer N, respectively (p<0.05): In treatment with low application rate of chemical fertilizer N, elevated CO2 and interaction of CO2 and O-3 significantly increased the amount of soil microbial biomass C by 25.32% and 38.59% (p<0.05), compared with CK, respectively.