The Characteristics Of Soil Microbial Community Structure In The Degraded Alpine Meadow After Different Restoration Measures Performed

Enclosure, laceration, reseeding, fertilization have been proved to be efficient ways in improvng vegetation and soil nutrient status in degraded grassland and the methods have been widely used on the alpine meadow in Maqu county, Gansu province. However, the specific process and mechanism of soil fertility improved by above measures are still unclear, especially for the alpine meadow. Soil microorganism is acting as the main driver for the decomposition of soil organic matter, and the characteristics of soil microorganism community structure were generally regarded as an important sensitive biological indicator for soil quality, which related closely to the release rate of bioactive nutrition.The aim of this thesis was to expose the specific process and mechanism of soil fertility improvement after the above measures were adopted in the degraded alipine meadow. Six measures including enclosure, laceration, reseedingl5 kghm-1, fertilization22.50 thm-1, laceration+reseeding 15 kg·hm-1, laceration+fertilization 22.50 t·hm-1 were conducted for restoring the degraded alpine meadow in Maqu County, and the free grazing grassland was set as the control. We analyzed the soil microbial community structure after the different restoration measures were performed, and the relationship among soil microbial community structure characteristics with soil nutrient characteristics, aboveground vegetation community structure were analyzed systematicly. The results showed that:(1) The number of different soil microorganism functional groups were significantly affected by the restoration measures. For soil bacteria, the amount was significantly higher in the enclosed grassland than that in the control and other restoration measures treatments (P<0.05); Followed by reseeding and fertilization grassland which alao had higher amount of bacteria than that in the control treatment, but had no significant difference with laceration+reseeding and laceration+fertilization treatments; laceration and grazed treatments given the lowest bactiria amount among the treatment. For soil fungi, the number under laceration+fertilization and enclosure grassland was significantly higher than that under other treatments (P<0.05), and no significant difference was found among those treatments. Enclosure, aceration+reseeding, laceration+fertilization, reseeding and fertilization significantly increased soil actinomycetes amount.compared with the grazing treatment,(2)The highest value in average well color development (ACWD) and Mclntosh diversity index of soil microorganisms was found under simply laceration treatment, followed by the enclosed grassland. The values under the simple fertilization treatment were lower than that under the comprehensive treatments of laceration+fertilization. There was no significant different between reseeding and laceration+reseeding treatments. With principal component analysis for carbon resourse use efficiency by soil microbes under these six treatments, the results showed that laceratin could significantly affect soil microbial functional diversity, and the diversity were obviously different under enclosure and laceration treatments than other treatments, slight difference was found between laceration+reseeding with reseeding treatments;(3) With redundancy analysis on soil properties and soil microbial community structures under different measures, it showed that the main factors affecting the number of different soil microbial functional group was alkali-hydrolyzable nitrogen content in the enclosure grassland, soil catalase content in the laceration+reseeding grassland. The main factor affecting soil microbial functional diversity was soil total phosphorus content in the reseeding grassland, soil total phosphorus and organic matter content in the laceration+reseeding grassland, and soil phosphatase, invertase and catalase in grazing, fertilization, reseeding and laceration+reseeding treatments, respectively.(4) With redundancy analysis on plant community traits and soil microbial community structures under different measures, it showed that the main factors affecting the number of different soil microbial functional group were species diversity index and evenness indexin under both enclosure and laceration measures treatments, plant community richness index in the fertilization treatment, gramineous biomass in the enclosure treatment. The main factor affecting soil microbial functional diversity was plant species diversity in both laceration and reseeding treatments, both sedge and gramineous biomass in reseeding treatment, gramineous biomass in both grazing and laceration+reseeding treatments.(5)The number of different soil microbial functional groups was affected by soil nutrients and soil enzyme activities. With simple correlation analysis, it indicated that, there was a negative relationship between soil bacteria number and soil organic matter content, total N content, soil urease activity, soil catalase activity, but positive correlation with soil pH value, polyphenol oxidase activity (P<0.05); There was positive correlation between soil actinomycetes and soil polyphenol oxidase activity, sucrase activity.(6) Soil microbial functional diversity was significantly affected by soil nutrient status especially soil organic carbon, which was the main factor. Soil microbial community functional diversity was significantly correlated with soil enzyme activity, and it showed the strong positive correlation with the soil catalase activity; while, it showed negative correlation with polyphenol oxidase activity. The most sensitive in the main carbon resource to changes of both soil nutrients and soil enzyme activitis were carbohydrates, amino acids and phenols, which indicated that the number of different soil microbial functional groups may be limited by soil humus, utilization of carbon source and nitrogen.(7) The number of different soil microbial functional groups and soil microbial functional diversity were significantly affected by total aboveground biomass, and the legume biomass was positively correlated with the amount of soil microbial functional groups. While both forbs and legume biomass were the main factors that affectisoil microbial function diversity. The number of different soil microbial functional groups correlated positivly with plant species diversity (P<0.05); The plant diversity index was the main factor that affect soil microbial community, less power factors following by the species richness and evenness. The most sensitive factor in the main carbon resource to changes of vegetation biomass were carboxylic acids, carbohydrates and amino acids,. The most sensitive factor to the changes of vegetation diversity were carboxylic acids and ammonia sugar. The result indicated that vegetation characteristics might affect soil microbial functional diversity by root exudates, the microbial activity and plant growth might be mainly limited by soil nitrogen supply in the studied area.