短期氮添加对荒漠草原土壤微生物特征的影响

Effects of Short-term Nitrogen Addition on Soil Biological Properties in Desert Steppe

为探究荒漠草原土壤微生物特征对短期氮添加的响应,以宁夏荒漠草原为对象,参照国内外同类研究和当地的氮沉降量,设置N0、N1、N2、N3、N4的5个处理,其纯氮添加量分别为0,2.5,5,10,15 g/(m^(2)·a),以尿素为氮源进行为期2年的氮添加试验,对不同氮添加处理下荒漠草原浅层土壤微生物特征进行了研究。结果表明:(1)随氮添加量的增加,荒漠草原0—20 cm土层土壤铵态氮含量呈升高的变化趋势,硝态氮含量呈先升高后下降的变化趋势。在0—10 cm土层,N1、N2、N3、N4处理草地铵态氮含量较N0处理分别增加了109.61%,136.52%,197.19%,198.88%,硝态氮含量以N2处理草地最高,显著高于N0、N3、N4处理(P<0.05)。(2)与N0相比,施氮后0—10 cm土层土壤微生物量氮含量显著下降,N1、N2、N3和N4处理分别较N0处理降低了37.54%,38.11%,28.56%,29.81%。(3)随氮添加量的增加,荒漠草原0—10 cm土层土壤真菌数量呈逐渐减少的变化趋势,N0、N1处理草地显著大于N3、N4处理草地(P<0.05)。PcoA分析显示高氮添加处理(N3、N4)对荒漠草原土壤amoA区、nirK区微生物的群落结构有显著改变。高氮添加(N3、N4)会对荒漠草原土壤微生物群落产生负面影响,具体表现为真菌数量减少,硝态氮含量降低,氮转化微生物的α多样性和优势菌丰度降低,群落结构发生显著改变。

Desert steppe belongs to the arid type of grassland,with low nutrient content,fragile ecological environment and sensitive response to disturbance.The gradual increase of global nitrogen deposition changed the process of carbon and nitrogen transformation in the ecosystem and affected soil properties.In order to explore the effects of nitrogen addition on biological properties of soil in desert steppe,we took the desert steppe in Yanchi County as the research object and set up 5 nitrogen treatments as N0,N1,N2,N3 and N4.These treatments were set based on the pure nitrogen addition levels of 0,2.5,5,10 and 15 g/(m^(2)·a),by applying with urea as nitrogen source.Results showed that:(1)The NH_(4)^(+)-N content in 0—20 cm soil layer of desert steppe increased with the increase of nitrogen application rate,while the NO_(3)^(-)-N content increased firstly and then decreased.In 0-10 cm soil layer,compared with N0,the NH_(4)^(+)-N contents under N1,N2,N3 and N4 treatments were increased by 109.61%,136.52%,197.19%and 198.88%,respectively.The NO_(3)^(-)-N content was the highest in N2 treatment,which was significantly higher than those in N0,N3 and N4 treatments(P<0.05).(2)Compared with N0,the MBN contents in 0-10 cm soil layer were significantly decreased by N1,N2,N3 and N4 treatments,which were reduced by 37.54%,38.11%,28.56% and 29.81%,respectively.(3)With the increase of nitrogen addition,the number of fungi in 0-10 cm soil layer of desert steppe gradually decreased,among treatments,the N0 and N1 were significantly higher than N3 and N4(P<0.05).PCoA analysis showed that the microbial community structure in amoA and nirK zones of desert steppe soil were significantly changed by high nitrogen addition.Based on this research,the high nitrogen addition(N3,N4)had negative effects on soil microbial community in desert steppe,which were as follows:the number of fungi decreased,NO_(3)^(-)-N content decreased,α diversity and dominant bacteria abundance of nitrogen-transforming microorganisms decreased,and the microbial community structure of nitrogen-transforming changed significantly.