Analysis On Responses Of Plant,Soil And Microorganism To Exogenous Nutrient Addition In Degraded Alpine Meadows

Looking at the scientific and reasonable schemes in management,restoration,and reconstruction of the alpine degraded meadows through fertilizer addition,this study was conducted at the lightly,moderately,and heavily degraded alpine meadows in the Keqihetan area at Henan Mongolian Autonomous County in Qinghai Province.Firstly,comparative experiments were designed with the different ratios of nitrogen-phosphorus-potassium in the fertilizers.Then,the effects of these fertilizers on the alpine meadows were evaluated,followed by the confirmation of appropriate ratios for differently degraded alpine meadows.Based on the above appropriate ratios of nitrogen-phosphorus-potassium in the fertilizers,treatments using manure replaced by chemical fertilizers（with different amounts and nitrogen forms）were conducted.After that,changes in the diversity and structure of plant and microbial communities,soil carbon-nitrogen-phosphorus stoichiometry,soil microbial biomass carbon,and nitrogen during three years of treatments were anlysized.The results were as follows:（1）Scarce nitrogen/phosphorus and adequate potassium elements were detected in the alpine meadows with different degrees of degradation.For fitting the equations of fertilizer response functions,the optimal nitrogen fertilizers for light,moderate,and heavy degraded alpine meadows were 145.0 kg/hm²～150 kg/hm²,200.0 kg/hm²～220.5 kg/hm²,and 205.9 kg/hm²～220.9 kg/hm² respectively.The optimal phosphorus fertilizers for light,moderate,and heavy degraded alpine meadows were 90.0 kg/hm²～92.0 kg/hm²,100.0 kg/hm²～122.3 kg/hm²,and 135.0kg/hm²～154.3 kg/hm² respectively.（2）Different fertilizer addition could increase the aboveground,underground and total biomass of plants,as well as the community richness and diversity in alpine meadows with different degradation levels.Compared with no fertilizer treatment,the plant biomass of the optimal fertilizer treatment could increase by more than50%.Moreover,the importance degree of grass significantly increased with the treatment extension and amounts of fertilizer addition.However,the importance degree of weed decreased significantly.Besides,the important degree of legume showed no significant difference among treatments.More importantly,the richness and evenness of the plant communities both increased in the treatments with fertilizer addition.（3）The abundance and diversity of soil bacterial community diversity were significantly affected by the degraded degree of the alpine meadows.The abundance and diversity indices significantly decreased with the increase of degradation.The OTU number,species richness,and evenness in the samples of light degraded samples were all the lowest,while higher in the samples of moderate and heavy degraded degrees.Compared with lightly degraded meadow,the moderately and heavily degraded alpine meadows were more suitable to be restored through fertilization practices,in the perspective of maintaining the soil microbial diversity.（4）With the treatment extension and the accumulated amounts of fertilizer addition,soil organic matter,organic carbon,total nitrogen,total phosphorus,C-N-P stoichiometry,and microbial biomass C-N stoichiometry all increased in alpine meadows with different degradation degrees.（5）Based on the information of vegetation community,soil physicochemical properties,soil ecological stoichiometry,soil microbial community structure and diversity to three kinds of fertilizers in the different degraded alpine meadows,the results showed that the optimal amounts of nitrogen and phosphorus fertilizer for the lightly,moderately,and heavily degraded alpine meadows were N:105 kg/hm² and P:105 kg/hm²,N:155 kg/hm² and P:122 kg/hm²,and N:155 kg/hm² and P:153kg/hm²,respectively.The optimal amounts of organic fertilizer for the different degraded alpine meadows were N:120 kg/hm²、P:18 kg/hm² and OF:690 kg/hm²,OF:5100 kg/hm²,and OF:5100 kg/hm²,respectively.The optimal amounts of different nitrogen forms of fertilizer for the different degraded alpine meadows were NH₄⁺-N:162 kg/hm²and NO₃-N:467 kg/hm²,NH₄⁺-N:162 kg/hm²and CO（NH₂）₂:147 kg/hm²,and NO₃-N:530 kg/hm²,respectively.