Impacts of enhanced ultraviolet-B radiation on CO2 emission from soil-soybean system.

To investigate the impacts of enhanced UV-B radiation on carbon dioxide(CO2) emissions from soil-soybean system,field experiments and outdoor pot experiments were carried out during two growing seasons under the condition of simulating 20% enhancement of UV-B. Carbon dioxide emissions were measured by static chamber-gas chromatograph method. Enhanced UV-B radiation did not change the seasonal pattern of CO2 emission from soil-soybean system but significantly decreased the flux of CO2 during pod-maturity stage(49.03% and 48.13% in 2004 and 2006,respectively) and the cumulative amount of CO2(43.26% and 44.79% in 2004 and 2006,respectively) . In addition,it had no significant impact on CO2 emission before podding. A biomass clipping method was employed to distinguish the influence of enhanced UV-B on CO2 flux from soybean plant and soil in different developmental stages. Both CO2 emissions from soils during the branching-flowering stage and those from soybean plants during the pod-maturity stage were significantly decreased by enhanced UV-B. Agroecosystem CO2 emissions declined by enhanced UV-B radiation were primarily due to the decrease in CO2 emissions from soybean plants rather than from soil. Enhanced UV-B reduced the fixed carbon by 352.73 g/m2CO2 during the branching flowering-podding stage,and by 1456.25g/m2CO2 during podding-seed filling stage. Enhanced UV-B radiation could reduce CO2 emissions fluxes from soybean ecosystem and decrease the fixed carbon.