Effects Of Warming And Enhanced UV-B Radiation On Soil Carbon Nitrogen Exchange And Biomass Of Soybean-winter Wheat Rotation System

Global warming, as well as the enhancement of surface ultraviolet-B radiation due to stratospheric ozone depletion is a major environmental issue, which has attracted wide attention from governments and the international academic community. As an important source or sink of the greenhouse gas emissions, the agroecosystem is intensively affected by climate change. In this study, field experiments including soybean and winter-wheat growing seasons in the open-top chambers were performed. There are four treatments in the soybean growing season, which are the control (CK), the 20% enhancement of UV-B radiation (U), the diurnal warming treatment (T), and the diurnal warming with 20% enhancement of UV-B radiation treatment (UT). Each treatment has three replicates. There are two treatments in the winter-wheat growing season, which are the control (CK), and the 20% enhancement of UV-B radiation (U). Infrared radiation heating pipes are used for diurnal waeming. The UV-B radiation is enhanced by using the UV-B radiation lamps. To investigate the effects of diurnal warming and enhanced UV-B radiation on CO2 and N2O emission from the cropland soil, soil CO2 and N2O fluxes were analyzed by static chamber-gas chromatography method. Furthermore, this study will provide a basis for the assessment on the trend of soil greenhouse gas emission from agroecosystem.Results showed that during the soybean growing season, different treatments of warming and enhanced UV-B radiation did not change the seasonal patterns of soil CO2 emission fluxes. Compared with CK, U, T, and UT treatments did not significantly change soil CO2 emission fluxes. Compared with UT, U significantly increased soil CO2 emission fluxes during the trileaf-branching stage, and warming reduced soil CO2 emission fluxes during the trileaf-branching stage. There was a significantly exponential relationship between soil CO2 emission fluxes of U, T, UT and soil temperature. Moreover, U, T, and UT increased the temperature sensitivity of soil CO2 emission fluxes in soybean plots. No significantly exponential relationship between soil respiration and soil moisture was found.In the soybean growth season, enhanced UV-B radiation treatment has changed the seasonal patterns of soil N2O emission fluxes during the trileaf-branching stage. Compared to CK, T significantly changed soil N2O emission fluxes during the trileaf-branching stage, the flowering-podding stage and the whole growth period, and U significantly changed soil N2O emission fluxes during the flowering-podding stage and the whole growth period. UT, compared to CK, significantly changed soil N2O emission fluxes during the trileaf-branching stage and the whole growth period. There was a significantly exponential relationship between soil temperature and soil N2O emission fluxes of CK and U, while T and UT did not have such significantly exponential relationship. And U, T, and UT reduced the temperature sensitivity of soil N2O emission fluxes in soybean-planted plots. However, there was a significantly exponential relationship between soil N2O emission flux and soil moisture.During the soybean growth season, compared to CK, U significantly reduced the aboveground biomass and the total biomass of the soybean, and T significantly reduced the aboveground biomass. UT, compared to CK, significantly reduced the aboveground biomass and the total biomass of the soybean. U, T and UT treatments did not significantly change the underground biomass of soybean.During the winter wheat growth season, enhanced UV-B radiation did not change the seasonal patterns of soil CO2 emission fluxes under the background of warming. Compared to CK, U significantly increased soil CO2 emission fluxes during the turning-green stage in the winter wheat plots. There was a significantly exponential relationship between soil temperature and soil CO2 emission fluxes for CK and U treatments, and the temperature sensitivity of soil CO2 emission fluxes in the winter wheat-planted plots could be reduced by diurnal enhanced UV-B radiation under the background of warming. However, there was a significantly exponential relationship between soil CO2 emission flux and soil moisture.During the winter wheat growth season, enhanced UV-B radiation did not change the seasonal patterns of soil N2O emission fluxes under the background of warming. Compared with CK, U significantly increased soil N2O emission fluxes during the turning-green stage, and U significantly reduced soil N2O emission fluxes during the elongation-booting stage. There was no significantly exponential relationship between soil temperature and soil N2O emission flux for CK and U treatments. There was a significantly exponential relationship between soil moisture and soil N2O emission flux for CK. However, there was no significantly exponential relationship between soil moisture and soil N2O emission flux for the U treatment.During the winter-wheat growth season, compared to CK, U treatment significantly reduced the aboveground biomass, underground biomass and total biomass of the winter wheat.