Effects of UV-B-enhanced straw decomposition on soil nitrogen transformation microorganisms and enzyme activities
To clarify the effect of enhanced UV-B radiation on the chemical composition of rice straw,the characteristics of straw decomposition after enhanced UV-B radiation and its indirect effect on nitrogen transformation in paddy soil were explored.In this study,a field experiment was performed in terraced fields in Yuanyang(1 600 m above sea level),taking the local rice variety Baijiao Laojing as the research object.The effects of enhanced UV-B radiation(5.00 kJ·m-2)on the chemical composition of rice straw,straw degradation,and soil nitrogen transformation were studied.The results showed that:Enhanced UV-B radiation significantly decreased the cellulose content of rice straw,increased the lignin content,and increased straw lignin/nitrogen.The degradation rates of cellulose,lignin,and total nitrogen decreased by 38.7%,18.1%,and 25.8%,respectively.Compared with straw under natural light,the straw applied after UV-B radiation significantly decreased the number of soil nitrogen-fixing bacteria,ammonifying bacteria,nitrifying bacteria,and denitrifying bacteria,increase the activities of soil protease,ammonia monooxygenase,and nitrate reductase,and increased the soil nitrification and denitrification rates.The correlation analysis showed that the straw lignin/nitrogen was significantly negatively correlated with the straw degradation rate.The degradation rates of straw cellulose,lignin,and total nitrogen were significantly positively correlated with the nitrate reductase activity,and the latter was significantly,positively correlated with the N2O emission flux.The number of nitrifying bacteria was negatively correlated with the content of NO-3-N.This study showed that enhanced UV-B radiation inhibited the degradation of straw cellulose,lignin,and total nitrogen by increasing the straw lignin/nitrogen,decreased the number of soil ammonifying bacteria,increased the activities of ammonia monooxygenase and nitrate reductase,promoted the transformation of soil NH+4-N to NO-3-N,and increased the N2O emission flux.
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