模拟氮沉降对土壤酶活性和微生物组成的影响

氮沉降改变了草地生态系统的氮(N)素循环过程,由此带来的生态学效应已成为当前研究的热点。以乌鲁木齐周边短期围封草地为研究对象,通过模拟氮沉降实验,分析了自由放牧地和围封草地土壤酶活性和微生物组成,结合土壤养分及化学计量特征,探讨了氮沉降对短期围封草地土壤微生物组成及酶活性的影响,为该地区放牧草地的保护、恢复及管理提供理论依据。结果表明:(1)土壤有机碳(SOC)、全氮(TN)、全磷(TP)含量随围封年限的增加总体呈升高趋势,表明围封有利于提高土壤养分含量。与中国草地平均值相比,该草地土壤碳氮比(C/N)相对较高,碳磷比(C/P)、氮磷比(N/P)相对较低,表明该草地土壤有机质分解良好,有利于土壤碳(C)、磷(P)的释放,而土壤N素较为缺乏。(2)就不同围封年限而言,围封3年草地5-20cm层土壤真菌数量高于其它样地;围封3年草地表层土壤蔗糖酶与过氧化氢酶活性最高;围封7年草地放线菌数量最多,说明围封能够促进土壤微生物生长及酶活性的提高。(3)氮素添加对土壤真菌具有抑制作用,N5(4.6gN m^-2 a^-1)、N10(9.8gN m^-2 a^-1)处理显著增加了各样地土壤细菌数量,氮素添加对围封7年草地0-10cm层土壤放线菌无显著影响,而氮沉降显著增加了其它样地5-20cm层土壤放线菌数量,其中N5、N10处理下促进作用最明显;氮素添加对该草地土壤脲酶、蔗糖酶、过氧化氢酶均具有促进作用,N5、N10处理促进作用最明显。综合分析表明,氮沉降可直接或间接影响土壤微生物及酶活性,短期围封作为一种草地管理手段,对退化草地生态系统的修复具有一定作用,并可通过改善土壤理化性质、调节养分含量及其化学计量比来加速退化草地的恢复。

Effects of simulated nitrogen deposition on soil enzyme activity, microbial community composition and stoichiometric characteristics of short-term enclosed grassland around Urumqi

The increase of global nitrogen deposition has changed the nitrogen (N) cycle process of grassland ecosystems, and the resulting ecological effects have become the focus of current research. In this paper, the grassland with short-term enclosure years around Urumqi was taken as the research object. The soil enzyme activity and microbial composition of free grazing land and the enclosed grassland were analyzed by simulated nitrogen deposition experiment. Combined with soil nutrient and stoichiometric characteristics, the effects of nitrogen deposition on soil microbial composition and soil enzyme activity of short-term enclosed grassland were discussed, which provided theoretical basis for the protection, restoration and management of grazing grassland in this area. The results showed that: (1) the contents of soil organic carbon (SOC), soil total nitrogen (TN) and soil total phosphorus (TP) were generally increased with the increase of enclosure years, indicating that enclosure was beneficial to the improvement of soil nutrient content. Compared with the average value of grassland in China, the soil carbon/nitrogen (C/N) in this grassland was relatively high, and the soil carbon/phosphorus (C/P) and soil nitrogen/phosphorus (N/P) were relatively low, indicating that the decomposition of soil organic matter in this grassland was good, and was conducive to the release of soil carbon and phosphorus, while the soil nitrogen was relatively short. (2) The number of fungi in 5-20cm soil layer of the 3-year enclosed grassland was higher than that in other plots. The activities of sucrase and catalase were the highest in the surface soil of the enclosed grassland for 3 years; The number of actinomyces was the highest in the 7 years after enclosure, which indicated that enclosure could promote the growth of soil microorganisms and the improvement of soil enzyme activities. (3) Nitrogen addition inhibited soil fungi, and N5 and N10 treatments significantly increased the number of soil bacteria in various plots. Nitrogen addition had no significant effect on actinomyces in 0-10cm layer of grassland enclosed for 7 years, while nitrogen deposition significantly increased the number of actinomyces in 5-20cm layer of other plots, among which N5 and N10 treatments had the most obvious promoting effect; nitrogen addition could promote the activities of urease, sucrase and catalase in the soil of the grassland, and N5 and N10 treatments had the most obvious effect. Comprehensive analysis showed that nitrogen deposition could directly or indirectly affect soil microorganisms and enzyme activities. As a means of grassland management, the short-term enclosure had a certain effect on the restoration of the degraded grassland ecosystem, and could accelerate the restoration of the degraded grassland by improving soil physical and chemical properties, adjusting nutrient content and stoichiometric ratio.