Succession Of Soil Microbial Communities Across The Vegetation Chronosequences In Abandoned Farmland

China began to implementing the Grain for Green Project in the whole country in2002.,but how to evaluate the ecological benefits of returning farmland to forests is currently an important issue.This study selected farmland?succession starting point?,abandoned grassland,abandoned barren shrub,natural forest?succession end point?and transitional zone shrub on the banks of the Lancang River in Baijixun village,Weixi County,Yunnan Province as the research object.Analyze the change of soil properties and microbial community structure environmental factors,and explore the relationship between microbial community structure after returning farmland to forest,Reveal the changes of soil micro-organisms?fungi,bacteria,and functional micro-organisms?communities at different vegetation successional stages after returning farmland to forests,to provide data support for the comprehensive evaluation of the ecological benefits of returning farmland to forests.The main conclusions are as follows:?1?With the succession of vegetation on the abandoned cropland,the soil properties changed mainly due to the increase of organic matter?OM?,increase of soluble organic carbon?DOC?,decrease of NO₃^--N in soil.With the succession of vegetation,NH₄⁺-N and soil C/N are gradually increase.?2?Bacterial community diversity increased after farmland was abandoned,and the bacterial diversity in ecotone was higher than that in natural forests,but the community composition did not change significantly;in disturbed ecosystems?Transitional shrub?,bacterial communities diversity is higher than that of stable ecosystems;bacterial communities are mainly affected by pH and NO₃^--N,and the main influencing factor of bacterial community diversity in natural forests and transitional shrubs is C/N.?3?The vegetation in the aboveground part was changed from the herb stage to the woodland through the shrub stage.The community composition of the soil fungal community showed a clear change trend with the change of the vegetation,which was mainly reflected in the proportion of the population of the fungal population is Sordariomycetes?The decrease from 26%to 7%?,and the Agaricomycetes?from 12%to 39%?;the succession of fungi is more consistent with the succession of vegetation.?4?In the initial stage of returning farmland to forests,AOB decreased in the soil due to the loss of nitrogen fertilizer addition.As the vegetation succession,organic matter accumulates,direct ammonium nitrogen that can be used by plants increases,and the AOB content gradually increases.The AOA content in the soil decreased with the rise of C/N;and in our study,the soil nitrification was mainly driven by AOB.?5?The low pH and high C/N content of the soil inhibits the action of nitrogen-fixing microorganisms in the soil and reduces the amount of nitrogen-fixing microorganisms.When the vegetation litter contains difficult-to-decompose components,the available carbon source for nitrogen-fixing bacteria is insufficient and the activity of nitrogen-fixing bacteria is inhibited.Therefore,With the succession of vegetation,soil properties gradually change,which affects the abundance and diversity of soil microbial communities.The structure of the fungal community is more susceptible to the type of vegetation than bacteria.