| For the sustainable development of ecological environment,Grain for Green project has been implemented in China since 1999.However,most of the studies on the Grain for Green project have focused on the restoration of vegetation and improvement of soil properties on fallow land,but there is a lack of sufficient understanding of the successional characteristics of soil microbial communities after the return of farmland to forestry.Therefore,in this study,soil samples were collected in the arable land in central Jilin Province and its adjacent larch woodland that have been restored for twenty and forty years.The high-throughput and metagenomic sequencing technology was used to analyze the diversity,community structure,species composition and functional genes related to carbon transformation of bacteria and fungi,and the soil physical and chemical properties and enzyme activity related to soil carbon transformation were also measured.The research results are as follows:(1)Grain for Green project had significant effects on soil physicochemical properties and soil carbon conversion related enzyme activities.p H and OM contents increased by 17.24% and76.88% after reforestation,while available potassium(AK)and alkali-hydrolyzed nitrogen(AN)decreased by 52.48% and 36.93%.Soil available phosphorus(AP)content was significantly decreased first and then increased after reforestation,and AP of the forest land was 82.26%lower than farmland after 40 years of reforestation.The activity of soil cellulase and β-glucosidase increased by 111.9% and 90.55% compared with that of farmland after 40 years of reforestation,and the activity of soil sucrase increased first and then decreased.The activity of soil sucrase increased by 235.37% compared with that of farmland after 20 years of reforestation.(2)Grain for Green project had significant effects on the composition and diversity of soil microbial community.The diversity and richness of bacterial community in larch forest decreased by 4.31% and 26.4%,respectively,compared with farmland,while the fungal community increased by 28.74% and 60.17%,respectively.Both bacterial and fungal communities were significantly different after reforestation,however the difference in fungi was greater.The number of bacterial nodes,connections and the modularity increased after reforestation.The bacterial network was more stable,the average connectivity and clustering coefficient of the fungal network were lower,and the community structure was more stable after reforestation.The positive correlation number of the bacterial network and the fungal network was greater than the negative correlation number,and most of the bacterial species were in a symbiotic state.Acidobacteriota and Proteobacteria were the main bacterial species at different stages of converting farmland to forest.The different species of fungi mainly concentrated in Ascomycota and Basidiomycota.The interactions between bacterial and fungal communities changed after reforestation,the abundance of the common variation groups,Acidimicrobiia and Tremellomycetes increased significantly after reforestation.The results of cross-domain network analysis of soil bacteria and fungi showed that the node number and correlation of larch forest were the most complex,and the positive interaction decreased and the synergistic effect of soil bacteria and fungi decreased.(3)After reforestation,the abundance of genes related to carbon conversion were significantly different.The gene abundance of CAM crassulacean acid metabolism,C4-dicarboxylic acid,3-hydroxypropionic acid(3-HP)3-hydroxypropionate increased by 8.53%,16.93% and 2.37% after reforestation,respectively However,the gene abundance of Wood reductive acetyl-Co A pathway decreased by 7.14%.The abundance of genes encoding glycoside hydrolase(GH),polysaccharide lyase(PL),and auxiliary activity(AA)decreased after reforestation,while carbohydrate binding module(CBM)increased.In summary,this study found that the soil properties changed afterreforestation in central Jilin Province,with significant increases in soil organic matter and p H,and significant decreases in alkaline nitrogen.Soil bacterial diversity and richness were significantly reduced,and soil fungal diversity and richness were significantly increased.The structure of soil fungal and bacterial communities were significantly different after reforestation,and the difference in fungal community structure was greater than that of bacteria.Soil microorganisms had a larger and complex network after fallowing,and the microbial carbon conversion function changed significantly. |
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