Abstract:

The enhanced UV-B radiation has different effects on the agricultural ecosystem. This article aims to explore the effects of different UV-B radiation levels on soil carbon conversion and greenhouse gas emissions in a rice field. A local traditional rice variety, Baijiaolaojing, was cultivated in a paddy of Yuanyang Terraces with an artificial simulation of different UV-B radiation levels (0, 2.5, 5.0, 7.5 kJ∙m^-2). The effects of different UV-B radiation levels on the activities of enzymes related to soil carbon conversion, contents of active organic carbon and greenhouse gas emissions from the rice paddy during rice growing period were investigated. The results indicated that an enhanced UV-B radiation of 5.0 kJ∙m^-2 significantly increased the cellulase enzymes activity by 15.4%-37.7% in the rice paddy. However, the enhanced UV-B radiation of 7.5 kJ∙m^-2 significantly decreased the activities of cellulase, beta-glucosidase, polyphenol oxidase and sucrose enzymes. The enhanced UV-B radiation significantly increased the content of soluble organic carbon, and decreased the content of oxidizable organic carbon and microbial biomass carbon in rice paddy soils. The three UV-B radiation levels significantly decreased CH₄ emissions by 7.5%-30.6% from the rice paddy during the whole rice growth period. The enhanced UV-B radiation of 5.0 kJ∙m^-2 significantly increased CO₂ and N₂O emissions, while UV-B radiation of 7.5 kJ∙m^-2 reduced CO₂ and N₂O emissions from the rice paddy. In summary, the enhanced UV-B radiation reduced the global warming potential of the three greenhouse gases from the rice paddy. Moreover, there were significantly positive correlations between the activities of polyphenol oxidase enzyme with the contents of microbial biomass carbon and easily oxidized organic carbon (P<0.05), and a very significantly positive correlation between methane emission flux with microbial biomass carbon content (P<0.01). Thus, the enhanced UV-B radiation inhibited the activity of polyphenol oxidase, reduced the content of easily oxidizable organic carbon and microbial biomass carbon, and then decreased CH₄ emissions and increased CO₂ and N₂O emissions from the rice paddy at the rice growth period.

Key words: UV-B radiation, rice field soil, active organic carbon, invertase activity, greenhouse gas emission, global warming potential

摘要：

UV-B辐射增强对整个农业生态系统产生不同程度的影响,为探讨不同UV-B辐射增幅对稻田土壤碳转化和温室气体排放的影响,在元阳梯田稻田原位种植农家水稻品种白脚老粳,通过人工模拟不同UV-B辐射增幅（0、2.5、5.0、7.5 kJ∙m^-2）,研究不同UV-B辐射增幅对水稻生长期稻田土壤碳转化酶活性、活性有机碳含量和CH₄、CO₂、N₂O排放的影响。结果表明,5.0 kJ∙m^-2 UV-B辐射处理导致稻田土壤纤维素酶活性显著增加,增幅范围为15.4%—37.7%;而7.5 kJ∙m^-2 UV-B辐射导致土壤碳转化酶（纤维素酶、β-葡萄糖苷酶、多酚氧化酶和蔗糖酶）活性显著降低。UV-B辐射增强导致土壤溶解性有机碳含量显著增加,而易氧化有机碳和微生物量碳含量减少。3个强度的UV-B辐射增幅处理均使稻田CH₄排放量显著减少,降幅范围为7.5%—30.6%;5.0 kJ∙m^-2 UV-B辐射处理显著增加稻田CO₂、N₂O排放量,而7.5 kJ∙m^-2 UV-B辐射导致稻田CO₂、N₂O排放降低;综合而言,UV-B辐射增强导致稻田3种温室气体的全球增温潜能降低。此外,土壤中多酚氧化酶活性与微生物量碳、易氧化有机碳含量呈显著正相关（P<0.05）,CH₄排放通量与微生物量碳含量呈极显著正相关（P<0.01）。可见,随UV-B辐射增强稻田土壤多酚氧化酶活性降低,进而减少易氧化有机碳和微生物量碳含量,最终导致稻田CH₄排放减少、CO₂和N₂O排放增加。

关键词: UV-B辐射, 稻田土壤, 活性有机碳, 碳转化酶活性, 温室气体排放, 全球增温潜能