UV-B辐射增强对稻田土壤氮转化的影响

本文旨在探讨UV-B辐射增强对稻田土壤氮转化的影响。在元阳梯田原位种植当地传统水稻品种——白脚老粳,研究UV-B辐射增强(0、2.5、5.0 k J·m~(-2)和7.5 k J·m~(-2))对水稻生长期稻田土壤氮转化相关酶活性、无机氮含量及N_2O排放量的影响。结果表明:5.0 kJ·m~(-2)UV-B辐射增强处理导致水稻分蘖期和孕穗期土壤亚硝酸还原酶、脲酶活性显著降低;孕穗期时所有处理亚硝酸还原酶活性显著高于其他时期,分蘖期时所有处理脲酶活性显著高于其他时期;与对照相比,3个UV-B辐射增强处理导致成熟期硝酸还原酶、蛋白酶活性显著增加;孕穗期时2.5、5.0、7.5 k J·m~(-2)UV-B辐射增强处理硝酸还原酶活性显著高于其他时期,分蘖期时所有处理蛋白酶活性显著高于其他时期的相同处理。2.5 k J·m~(-2)UV-B辐射增强处理在水稻整个生育期中,除拔节期外NH_4~+-N含量均显著降低,5.0 kJ·m~(-2)UV-B辐射增强处理导致稻田土壤NO_3~--N含量在整个水稻生育期显著升高。UV-B辐射增强显著降低拔节期和孕穗期N_2O排放通量,成熟期则显著增加。相关分析发现,稻田土壤N_2O排放通量与NH_4~+-N含量呈极显著正相关,而NH_4~+-N含量与NO_3~--N含量及脲酶活性呈极显著正相关(P0.01)。从水稻生长的生育期来看,UV-B辐射提高了土壤硝酸还原酶、蛋白酶活性,抑制了亚硝酸还原酶、脲酶活性,促进了NH_4~+-N向NO_3~--N的转化,从而抑制了拔节期、孕穗期N_2O的排放。

Effects of enhanced UV-B radiation on nitrogen transformation in paddy soil

This paper aims to explore the effect of enhanced UV-B radiation on nitrogen transformation in rice paddy soil. A local traditional rice variety, Baijiaolaojing, was planted in Yuanyang terraced fields. The effects of enhanced UV-B radiation(0 kJ·m^-2, 2.5 kJ·m^-2, 5.0 kJ·m^-2, and 7.5 kJ·m^-2)on the activities of enzymes related to soil nitrogen conversion, inorganic nitrogen contents, and N₂O emission in rice paddy soils during rice growing period were investigated. The results showed that enhanced UV-B radiation(5.0 kJ·m^-2)significantly decreased the activities of nitrite reductase and urease in the soils at tillering and booting stages of rice. The activities of nitrite reductase at booting stage and urease at tillering stage were significantly higher than those at other stages. Compared to control treatment, the three enhanced UV-B radiation treatments significantly increased the activities of nitrate reductase and protease at the mature stage. Nitrate reductase activity at enhanced UV-B radiation treatments of 2.5, 5.0 kJ·m^-2, and 7.5 kJ·m^-2 at booting stage was significantly higher than that in other stages, and the protease activity for all treatments at tillering stage was significantly higher than that in other stages. Enhanced UV-B radiation at 2.5 kJ·m^-2 significantly decreased NH₄⁺-N content during the whole rice growth period except the jointing stage, while 5.0 kJ·m^-2 UV-B radiation significantly increased NO₃^--N content in paddy soil during the whole rice growth period. Enhanced UV-B radiation significantly reduced N₂O emission at jointing and booting stages, while it significantly increased N₂O emission at the mature stage. Correlation analysis indicated that N₂O emission flux from rice paddy soil significantly correlated with the NH₄⁺-N content, while the NH₄⁺-N content was significantly positively correlated with the NO₃^--N content and urease activity(P<0.01). At the rice growth period, enhanced UVB radiation increased the activities of nitrate reductase and protease, inhibited the activities of nitrite reductase and urease, promoted the transformation of NH₄⁺-N to NO₃^--N in rice paddy soils, and thus reduced N₂O emission at jointing and booting stages.