| Grassland degradation caused by long-term irrational use in recent decades is a prominent ecological problem in the typical grassland of Inner Mongolia,The scientific and rational use of grassland resources by adopting different adaptive use is not only the demand for the development of grass husbandry,but also an important hotspot of grassland ecology research.Therefore,studying the response of grassland net primary productivity and soil nitrogen mineralization to different adaptive use methods is of great significance to the protection of the plant community diversity of typical grasslands in Inner Mongolia and the rational use and sustainable development of grassland resources.This study relied on the Field Observation and Research Station of the Ministry of Education of the Typical Steppe,and took the Leymus chinensis grassland community in the typical steppe area of Inner Mongolia as the research object.Since 2012,three different treatments have been designed:enclosure(control),adaptive mowing(mowing once a year in August,Stubble height 6 cm),and adaptive grazing(grazing once a month from May to September,Stubble height 6 cm),each treatment was repeated 3 times.Through 9 years of long-term grassland adaptive use experiments,we observed the ANPP of grassland plant communities,the density and composition structure of plant communities,species diversity,soil physical and chemical properties,soil nitrogen mineralization rate,Changes in soil microbes and nitrogen transformation functional gene abundance and other indicators,Discuss the impact of different adaptive use methods on plant communities and soil-related indicators,and reveal the key adjustments between plant diversity,microbial diversity,and soil physical and chemical properties in typical grassland ecosystems between net primary productivity and adaptive use effect.The main conclusions are as follows:1.Grazing significantly increased the density of the plant community,and there was no significant difference between mowing and control.Functional group level:Both mowing and grazing significantly reduced the density of Rhizome grasses,and significantly increased the density of Clumping grasses and Annuals and Biennials plants,and the impact of grazing was higher than that of mowing.Dominant species level:Both mowing and grazing significantly reduced the population density of Leymus chinensis,and grazing was significantly lower than that of mowing.Both mowing and grazing significantly increased the population density of Stipa Krishii in the community,and mowing was significantly higher than grazing.Grazing also significantly increased the population density of Cleistogenes squarrosa,and it increased slightly under mowing,but it was not significantly different from the control.2.Mowing and Grazing have no significant effect on the species richness of the community,but significantly change the species uniformity of the plant community,which leads to a significant increase in the species diversity of the community under both mowing and grazing,and the increasing effect of mowing is somewhat lagging behind that of grazing.However,mowing is slightly higher than grazing,but there is no significant difference between the two use methods.3.The adaptive use promotes the compensatory growth of plants.Both mowing and grazing increase the ANPP of the plant community on the ground,and the effect of grazing is more significant than that of mowing.At the beginning of the experiment(2012-2014),the economic output of the plant community under the mowing method was higher than that of the grazing.With the increase of utilization time,the economic output of the plant community under the grazing method was significantly higher than that of the mowing.The ANPP of the plant community and the community diversity have a very significant negative quadratic function correlation,showing a unimodal pattern model(R2=0.1832,y=-2E-05x2+0.0072x+0.8427),the species diversity of plant communities is the highest in the middle level of productivity.4.Grazing significantly increases the temperature of the shallow 010cm soil and reduces the soil moisture content.Grazing significantly increased the soil temperature in the shallow layer of 0-10cm,and reduced the soil moisture content,and the soil appeared warm and dry.Mowing also increases the dryness of the soil,but the amplitude is less than grazing.The content of soil available nutrients is greatly affected by precipitation.Both adaptive mowing and grazing significantly reduced the content of soil available nitrogen,and the reduction rate caused by grazing was higher than that of mowing.5.The soil nitrogen mineralization rate in the research area is dominated by the nitrification rate.Precipitation has an important influence on the rate of soil nitrogen mineralization.In the period of steady precipitation,grazing significantly increased the rate of soil nitrification,thereby increasing the rate of soil nitrogen mineralization,and the effect of mowing on the rate of soil nitrogen mineralization was not significant.Soil bulk density and soil temperature have a significant positive correlation with soil nitrogen mineralization rate,and soil water content,soil nitrate nitrogen and available nitrogen content have a significant negative correlation with soil nitrogen mineralization rate.The total abundance of related functional genes involved in the process of nitrogen transformation showed an increasing trend under both mowing and grazing methods,and the increasing amplitudes were 18.7%and 30.2%,respectively.Mowing significantly increased the abundance of ureC,gdh,narG,and nasA functional genes,and grazing significantly increased the abundance of amoB,nirK,and nrfA functional genes.The change in the abundance of functional genes has a higher interpretation rate than the physical and chemical properties of the soil in response to nitrogen mineralization under different use.6.Both adaptive mowing and grazing increased the abundance of soil microbial communities,while mowing and grazing had little effect on the structure of soil microbial communities.Grazing promotes the growth and reproduction of thermophilic microorganisms in the soil,and inhibits the reproduction of acidophilic microorganisms in the soil.Soil temperature and soil nitrate nitrogen content are the main factors affecting the composition of the soil microbial community in the study area.7.There is a significant positive correlation between plant community diversity and microbial community diversity,and the interaction between the two is an important driving factor for changes in soil microbial diversity and plant community diversity.The soil microbial richness has a very significant positive correlation with ANPP of the plant community.There is a very significant positive linear correlation between the ANPP and soil nitrogen mineralization rate(R2=0.64,y=0.0616x-5.9912).Adaptive mowing and grazing have a significant positive effect on the ANPP of the plant community,and the positive effect of grazing is higher than that of mowing.Soil physical and chemical factors are the key factors that regulate the ANPP of different use methods and the community.It is an important management measure for the sustainable use of grassland.In addition,soil temperature and soil nitrate nitrogen content are the main factors influencing the changes in ANPP of the dominant group.This study found that adaptive mowing and grazing are beneficial to the increase in ANPP and community species diversity of typical grassland plant communities.Soil physical and chemical factors are closely related to the ANPP and community diversity of the community,and it plays a key regulatory role in the response mechanism of net primary productivity to different use.Compared with mowing,adaptive grazing can increase the diversity of plants and microorganisms,promote the material circulation process in the soil,increase the rate of soil nitrogen mineralization,and increase the ANPP of grassland.It can be used as an important management measure for grassland protection and sustainable use. |
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