| Under the mutual influence of global climate change,unreasonable utilization and other factors,alpine meadows have been degraded to varying degrees.With the grassland degradation,the original soil microenvironment was disturbed,and the corresponding soil microbial community structure was gradually formed.At the same time,the new microbial community had a reverse effect on the soil environment,thus changing its soil properties.Due to the technical limitation,and the lack of professional research and other factors,the function of more than 90% of soil microorganisms is not clear,and soil-microorganisms are lack of systematic research.In this research,the composition,pattern and function of soil microorganisms in non-degraded,lightly degraded,moderately degraded,severely degraded and extremely degraded(black soil beach)alpine meadows were studied by high-throughput gene detection techniques,and its driving factors such as vegetation characteristics and soil properties were studied to explore the contribution and response of grassland vegetation,soil microbial community structure and function characteristics,soil properties and enzyme activities to grassland degradation.To clarify the network regulation relationship among soil,fungi and bacteria in degraded grassland ecosystem.The results showed that:1.In the process of alpine meadow degradation,grassland plant species successively from Cyperaceae and Gramineae to Compositae and poisonous and other grasses species,and the dominance of fine forage grasses such as Kobresia mandshurica decreased continuously,while the important values of Chrysanthemum and Ligularia continued to increase.The species richness,diversity,dominance and biomass of grassland vegetation decreased significantly,but there was no significant change in evenness.More than 80% of the underground biomass is concentrated at the soil depth 0?10cm,and the moderate degradation stage is the turning point of vegetation degradation?2.With the aggravation of grassland degradation,soil water content decreased significantly,soil p H increased significantly,soil organic carbon decreased sharply in the early stage of degradation,but did not change significantly after moderate degradation,soil total nitrogen showed a downward trend as a whole,soil total phosphorus showed a V type change,soil total potassium showed an inverted-V type change,soil ammonium nitrogen and nitrate nitrogen content increased,available phosphorus content decreased,and available potassium content curve increased.In the process of degradation,soil C: N: P decreased significantly,and soil total and available nutrients showed an inflection point in the moderate degradation stage.3.The contents of soil microbial carbon and nitrogen in alpine meadow were 997?2823mg/kg and 282?450mg/kg respectively.More than 70% of soil microorganisms were concentrated in 0?10cm soil.The soil microbial biomass carbon and nitrogen in degraded grassland showed a V-shaped trend,and the contents in moderately degraded grassland were the lowest.The soil microbial C: N was 2.44?4.77,and decreased significantly with the aggravation of degradation.The change of soil urease activity was inverted-V type,and the phosphatase activity curve decreased.During the grassland degradation,soil microbial carbon source utilization activity,species composition and community structure have a large transition succession in the moderate degradation stage.4.Proteobacteria,acidobacteria,planctomycetes,verrucomicrobia and actinobacteria are the dominant bacteria in alpine meadows,while ascomycota,basidiomycota and mortierellomycota are the dominant fungi in soil.Grassland degradation significantly changed the species composition of soil fungi and bacteria,decreased the abundance of Proteobacteria,and increased the abundance of acidobacteria,planctomycetes and Gibberella(Fusarium)tricincta abundance.Grassland degradation had no effect on bacterial Chao1 index,lightly degradation increased bacterial Simpson index,decreased fungal Shannon index and Simpson index,severely degradation increased fungal Chao1 index and bacterial Shannon index,and extremely degradation significantly decreased bacterial Simpson index.5.The bacteria of material metabolism,environmental information processing and genetic information processing play the main functional regulatory role in soil,and chemical energy heterogeneity,nitrification,nitrite oxidation and sulfur metabolism are the dominant functional bacteria.Carbon,nitrogen,sulfur,iron and manganese metabolic bacteria were significantly different among different grasslands.Severely and extremely degradation increased the abundance of ammonia-oxidizing bacteria and decreased the abundance of sulfide,nitrite oxidation and urea hydrolysis bacteria.In the process of degradation,chemical energy anomalies,aromatic compound degradation and denitrification bacteria all showed "V" type changes,and the moderate degradation stage was the turing point in microbial community ecological function structure.The abundance of pathophytic,symbiotic and saprophytic fungi were significantly different in different grasslands.Saprophytic,symbiotic and transitional fungi were significantly enriched in non-degraded grassland,light degradation increased the abundance of saprophytic-symbiotic transitional fungi,and reduced the pathological fungi abundance,and the abundance of symbiotic fungi was reduced by severe degradation.The grassland degradation changed the community and functional structure of soil fungi and bacteria.6.Soil microbial diversity in alpine meadow has no relationship with vegetation diversity,but fungal diversity has a significant negative correlation with vegetation species richness and aboveground biomass.The soil microbial species composition was positively correlated with TN,TOC and SWC,and negatively correlated with TK and p H.Soil bacterial community and functional structure have no correlation with vegetation characteristics,fungal community structure was affected by aboveground biomass;soil SWC,p H,TOC,TN and TK play a major role in regulating microbial community and functional structure.Soil microbial carbon and nitrogen are closely related to vegetation coverage,species richness and biomass.The more complex the microbial community structure,the higher the soil microbial carbon and nitrogen content.Soil enzyme activity is mainly affected by soil fungi,and the relationship between soil bacteria and fungi is mutually beneficial symbiosis.The explanation rates of vegetation and soil factors to the changes of soil bacterial and fungal community structure and Faprotax functional structure were 85.69%,76.78% and 87.17%,respectively,in which soil factors could explain 48.45%,36.9% and 31.55% alone,and soil-vegetation interaction could explain 29.85%,32.68% and 50.74%,respectively.Compared with the soil microbial community structure,soil-vegetation interation has a greater impact on the microbial functional structure. |
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