| The rocky desertification caused by abandoned farming is a serious problem in karst areas of Southwest China.Restricted by the special geological conditions of carbonate rocks and natural disasters such as soil erosion,slow soil formation and the soil fertility continues to decline,which hinders the sustainable development of agricultural production and economic society.Although vegetation restoration is widely promoted as an effective measure of ecological restoration in karst areas,the slow recovery speed and unclear soil nutrient supply mechanism have been the major scientific and technological problems facing the control of rocky desertification.Soil microorganisms play an important role in nutrient supply.However,how microorganisms drive nutrient cycling in karst ecosystems at different vegetation restoration stages remains unclear.Therefore,in this study,the soil of abandoned grassland,natural secondary forest(15 years and 30 years)and primary forest in Daheishan area of Pingbian County,Yunnan Province was taken as the research object,and the community characteristics and response mechanism of microorganisms related to soil carbon,nitrogen,phosphorus and other nutrient cycles in different vegetation restoration stages were studied by using macro genome sequencing and other methods.Combining p H,organic carbon,inorganic nitrogen and other soil physical and chemical properties,this paper elucidates the microbial mechanism and driving factors of soil nutrient supply in the restoration process of fragile karst ecological area in southwest China,in order to provide a scientific theoretical basis for the comprehensive control of the key fragile ecological area of karst rocky desertification and the realization of green and sustainable development of agriculture.The main research conclusions are as follows:(1)There were significant differences(P<0.05)in functional genes related to carbon fixation in soil at different vegetation restoration stages in karst rocky desertification area,and the contribution of reductive citrate cycle functional genes was the largest in all soils.The abundance of carbon fixation genes in grassland stage was significantly higher than that in the two secondary forests and virgin forests(P<0.05),indicating that grassland soil had stronger carbon sequestration potential in the early stage of vegetation restoration.Proteobacteria is the main contribution species to carbon fixation,and its contribution decreased with the restoration of grassland to virgin forest.Redundancy analysis showed that soil bulk density,total nitrogen and nitrate nitrogen were the key environmental factors driving the function and distribution of nutrient supplying microorganisms in different vegetation in karst rocky desertification area.(2)There were significant differences in the abundance of nitrogen cycle function genes in different vegetation succession stages(P<0.05),and the abundance of organic nitrogen metabolism genes was the largest in all stages,suggesting that organic nitrogen mineralizing microorganisms were the key factor of soil nitrogen supply in karst rocky desertification area.The abundance of nitrogen fixation genes decreased significantly with vegetation restoration(P<0.05),indicating that nitrogen-fixing microorganisms were particularly important in the early restoration of karst rocky desertification.The abundance of nitrification genes increased significantly with vegetation restoration(P<0.05),and Nitrospirae and Candidatus Rokubacteria were the main microbial species in different vegetation soils,The results indicated that the regulation of soil microorganisms at the species level along with vegetation succession improved the supply and cycling function of soil nitrogen nutrients.Redundancy analysis showed that contents of soil total carbon,total nitrogen,nitrate nitrogen and calcium were the main environmental driving factors of vegetation transformation from grassland stage to primary forest stage in karst rocky desertification area.(3)There were significant differences in phosphorus cycling functional genes in different vegetation succession stages(P<0.05).The abundance of phosphorus cycling functional genes in grassland stage was higher than that in secondary forest and virgin forest,and gradually decreased with the process of grassland restoration to primary forest.Among all vegetation soils,the abundance of phosphorus transport functional genes was the largest.The results showed that phosphorus transporter microorganisms were important factors to promote the effective circulation of phosphorus in vegetation and soil.Proteobacteria and Acidobacteria are the main dominant species of phosphorus cycling in the natural ecosystem after abandoned farmland in karst rocky desertification area,and their abundance decreased gradually with the progression of vegetation recovery,suggesting that these microorganisms were the main limiting species of phosphorus nutrient supply in the early succession.In the secondary forest stage of 30 years,both the phosphorus cycling genes and functional microorganisms exhibited high similarity to those in the virgin forest,indicating that after 30 years of natural succession in typical karst rocky desertification areas,the species and functional diversity of phosphorus cycling microorganisms in secondary forest ecosystems have approached that of the virgin forest ecosystem before abandonment. |
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