Effects Of Vegetation Restoration On Autotrophic Microbial Communities And Carbon Sequestration Capacity

Land degradation is an important environmental problem that threatens the global ecological balance.To prevent the soil quality deterioration,vegetation plantation is widely used for ecological restoration of degraded soils.However,the poor nutrients of degraded soils restrict the normal growth of vegetation and reduce the ecological restoration effect.Autotrophic microorganisms can convert atmospheric CO₂ into their own nutrients through photosynthesis or chemoenergetic synthesis.In the process of vegetation restoration of degraded soil,especially at the early stage of vegetation restoration,carbon sequestration by autotrophic microorganisms may be a significant nutrient source for plant growth.It is important to reveal the carbon sequestration capacity of autotrophic microorganisms and its influencing mechanism in the process of vegetation restoration.In this study,the high-throughput sequencing,¹³C stable isotope tracing technology and molecular ecological network analysis were used to analyze the autotrophic microbial community,molecular ecological network and carbon sequestration capacity of autotrophic microorganisms during the vegetation restoration of degraded soils.The main factors influencing the carbon sequestration capacity of autotrophic microorganisms were analyzed by using structural equation modeling.The main results were as follows:（1）Soil bulk intensity showed a decreasing trend during the vegetation restoration of degraded soil,while soil porosity exhibited the opposite trend.Increases in soil nutrient,microbial biomass carbon and nitrogen contents were observed during the vegetation restoration of degraded soil.The ratio of microbial biomass carbon and nitrogen at the early and late stage of vegetation restoration were 1.72 and 1.98 times higher than that at the non-restoration stage,respectively.The proportion of available nitrogen to total nitrogen at the non-restoration and early stages increased by 28.9%and 40.1%,respectively,compared with that at the late stage.The results indicated that the vegetation restoration is beneficial to increase soil nutrient content.（2）The species diversity of autotrophic microorganisms was highest at the early stage,while the autotrophic microbial abundance at the late satge was much higher than that at the non-restoration and early satge of vegetation restoration.Proteobacteria,Rhodobacteraceae and Rhodobacter were the most dominant autotrophic microbial phyla,families,and genera in soils with different restoration stages,respectively.Soil organic carbon,dissolved organic carbon and total nitrogen were the key factors affecting the autotrophic microbial communities during the vegetation restoration process.The results of molecular ecological network analysis showed that the connection between autotrophic microorganisms network modules was tighter at the early stage than that at the late and non-restoration stages.Hydrogenophaga and Rhodobacter were the key genera in the molecular ecological network of autotrophic microorganisms.The species diversity of soil autotrophic microbial taxa was richer and the molecular ecological network was more complex at the early stage than that in the non-restoration and late stages.（3）The microbial carbon sequestration rate at the non-restoration and early stages was 2.15 and 1.52 times higher than that at the late stage,respectively.The microbial carbon sequestration rate showed a trend of first increasing and then decreasing during the vegetation restoration.The annual organic carbon fixed by autotrophic microorganisms was 2.05%,2.53%and 0.55%of the total soil organic carbon in non-restoration,early and late satges,respectively,implying the important role of autotrophic microorganisms in the accumulation of soil organic matter at early stage of vegetation restoration.Among the abiotic factors dissolved organic carbon showed the strongest correlation with the carbon sequestration capacity of autotrophic microorganisms,followed by soil organic carbon,total nitrogen,and available nitrogen,all of which showed negative effects.The results of partial least squares structural equation modeling showed that soil nutrients had a significant negative effect on microbial carbon sequestration capacity,while the autotrophic microbial community had a limited effect on it.The highest rate of carbon sequestration by autotrophic microorganisms was observed when the dissolved organic carbon was close to 79.11 mg kg^-1 and the relative abundance of Rhodobacter was close to 50.23%.In summary,the abundance of autotrophic microorganisms responded positively to the vegetation restoration of degraded soils,and the highest species diversity and molecular ecological network complexity of autotrophic microorganisms were observed at the early stage of vegetation restoration.The carbon sequestration rate of autotrophic microorganisms showed a trend of first increasing,and then decreasing with the vegetation restoration.Compared with the autotrophic microbial community,the effect of soil nutrients on the carbon sequestration capacity of autotrophic microorganisms was more significant.Appropriately increasing soil dissolved organic carbon contributes to promote the vegetation restoration effect of degraded soil.The results of this study are of great significance to guide the vegetation restoration of degraded soil.