宁南山区退耕还林还草对土壤氮素组成及其转化酶活的影响

Effects of Converting Farmland into Forest and Grassland on Soil Nitrogen Component and Conversion Enzyme Activity in the Mountainous Area of Southern Ningxia

以宁夏南部山区柠条、山桃、苜蓿和长芒草这4种植被为研究对象,玉米(农地)为对照,测定土壤中7种氮素的含量及2种氮素转化相关酶的活性,通过冗余分析方法探究退耕还林还草对土壤氮素及其转化酶活的影响.结果表明:①与玉米地相比,长芒草地的颗粒有机氮,轻组分有机氮,微生物生物量氮和铵态氮分别增加35. 3%、83. 3%、64. 2%和110. 0%;苜蓿地的可溶性有机氮和铵态氮分别增加0. 7%和67. 5%;长芒草地的天冬酰胺酶和蛋白酶活性活性分别提高360%和144. 8%,说明退耕还草对氮素及其转化酶有一定促进作用;②山桃地的有机氮、轻组分有机氮、颗粒有机氮和可溶性有机氮分别比玉米地高3. 7%、133. 3%、70. 6%和28. 1%,柠条地的轻组分有机氮和山桃地的微生物生物量氮分别比玉米地高16. 7%和49. 6%,柠条地和山桃地的蛋白酶活性均高于玉米地,说明退耕还林对氮素及其转化酶同样有促进作用.③冗余分析(RDA)结果和环境因子解释率表明,土壤含水率,p H值和有机碳是影响宁南山区氮素分布与转化的关键因子.退耕还林还草改变了氮素相关转化酶的活性、对氮素组成有一定的促进作用,为黄土高原生态恢复和土壤质量管理提供了理论依据.

The effects of the policy of converting farmland to forest and grassland on soil nitrogen content and conversion enzyme activity were studied. Caragana intermedia,Prunus davidiana,Medicago spp.,and Stipa bungeana and a corn control were examined to determine the concentrations of seven soil nitrogen components and the activity of two nitrogen conversion enzymes. The main factors affecting soil nitrogen distributions and transformation was also explored using redundancy analysis( RDA). The results showed that:① Compared with the corn soil,the content of particulate organic nitrogen,light fraction organic nitrogen,microbial biomass nitrogen,and ammonium nitrogen in the Stipa bungeana soil increased by 35. 3%,83. 3%,64. 2%,and 110. 0%,respectively;soluble organic nitrogen and ammonium in the Medicago spp. soil increased by 0. 7% and 67. 5%,respectively;the asparaginase and protease activities in the Stipa bungeana soil increased by 360% and 144. 8%,respectively,indicating that conversion of farmland to forest and grassland has a promoting effect on nitrogen components and conversion enzyme activity;② The content of organic nitrogen,light organic nitrogen,particulate organic nitrogen,and soluble organic nitrogen in the Prunus davidiana soil was 3. 7%,133. 3%,70. 6%,and 28. 1% higher than that of the corn soil,respectively. The light fraction organic nitrogen content of the Caragana intermedia soil and microbial biomass nitrogen content of the Prunus davidiana soil was 16. 7% and 49. 6% higher than that of the corn soil,respectively. Protease activity in the Caragana intermedia and Prunus davidiana soils was higher than in the corn soil,further indicating that the conversion of farmland to forest and grassland promotes the accumulation of nitrogen components and enhances conversion enzyme activity;③ The RDA and environmental factor explanation rate results indicated that soil water content,p H,and soil organic carbon were the key factors affecting nitrogen distribution and transformation in the mountainous area of southern Ningxia.Overall,the results show that converting farmland into forest and grassland has changed conversion enzyme activity and has promoted the accumulation of nitrogen components in soils. This provides a theoretical basis for ecological restoration and soil quality management in the Loess Plateau.