地表UV-B辐射增强对土壤-大豆系统N2O排放的影响

通过大田试验和室外盆栽试验,采用人工增加紫外辐射的方法模拟UV-B辐射增强,用静态箱-气相色谱法测定N_2O排放通量,研究地表UV-B辐射增强对土壤-大豆系统N_2O排放的影响.结果表明:在相同的气象条件和田间管理措施下,UV-B辐射增强没有改变土壤-大豆系统N_2O排放通量的季节性变化规律.但从植株结荚到成熟,UV-B辐射增强降低了土壤-大豆系统N_2O排放通量,进而降低了N_2O的累积排放量.收割实验发现,在分枝开花期,UV-B辐射增强对土壤N_2O排放影响明显,降低了土壤N_2O排放通量;从结荚至鼓粒期,UV-B辐射增强主要通过降低植株地上部分N_2O排放通量来降低土壤-大豆系统的N_2O排放.UV-B辐射增强显著降低了植株的生物量,并影响到植株的氮代谢和土壤NH_4~+-N与微生物氮.UV-B辐射增强可能会导致农田生态系统N_2O排放量降低.

Impacts of enhanced UV-B radiation on N2O emissions from soil-soybean systems

Global warming and enhanced ultraviolet radiation on the earth′ surface are of the two most concerns in the global change. These two environmental problems are primarily caused by increasing of greenhouse gas concentration in atmosphere and exhaustion of stratospheric ozone, respectively. It is well documented that enhanced ultraviolet radiation has an effect on crop growth, which may also have impacts on greenhouse gases emissions from agroecosystem. To investigate the impacts of enhanced UV-B radiation on nitrous oxide (N_2O) emissions from soil-soybean systems, field and outdoor pot experiments were carried out during two growing seasons under the condition of simulating 20% enhancement of UV-B. Nitrous oxide emissions were measured by static chamber-gas chromatograph method. Results indicated that the enhanced UV-B radiation did not change the seasonal pattern of N_2O emission from soil-soybean system, while it declined the flux and cumulative amount of N_2O during pod-maturity stage. A biomass clipping method was employed to distinguish the influence of enhanced UV-B on N_2O flux from soybean plant and soil in different developmental stages. Both N_2O emissions from soils during the branching-flowering stage and those from soybean plants during the pod-filling stage were significantly decreased by the enhanced UV-B. Agroecosystem N_2O emissions declined by enhanced UV-B radiation were primarily due to the decrease in N_2O emissions from soybean plants rather than from soil. In contrast with the control, enhanced UV-B radiation remarkably decreased soybean biomass, changed the process of the nitrogen metabolism of soybean plant, and significantly raised the soil available nitrogen and soil microbial biomass ratio of C/N. The results of this study suggested that enhanced UV-B radiation could reduce N_2O emissions from agricultural ecosystems.