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 kg N hm-2) application rate of chemical fertilizer N exposed to the elevated CO2, O3, CO2 plus O3 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 O3 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 O3 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 O3, 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 O3 significantly increased the amount of soil microbial biomass C by 25.32% and 38.59% (p<0.05), compared with CK, respectively.