Soil microbial community and their functional genes during grassland restoration

Soil microbial functional genes are linked with carbon (C) as well as nitrogen (N) cycling processes, and their relative abundances are strongly affected by ecosystem managements. Yet, soil microbial community compositions and their C, N cycling genes' abundance in temperate grasslands remain poorly studied. Here, the Illumina MiSeq sequencing (16 S rRNA gene and internal transcribed spacer [ITS]) and meta-genomic GeoChip sequencing technologies were used to explore the alterations of microbial compositions and functional genes in the topsoil (0-10 cm) following grassland restoration. Grassland restoration increased the relative abundances of the copiotrophs (such as Actinobacteria, Proteobacteria, Bacteroidetes), but reduced the oligotrophs (including Acidobacteria, Chloroflexi, Planctomycetes), suggesting that microorganisms shifted from oligotrophic to copiotrophic groups during grassland restoration. The changes in microbial eco-strategies were also supported by the meta-genomic GeoChip sequencing data. In the early restoration years, the microbial functional genes were dominant with recalcitrant C degradation (pgu, glx, lig, mnp), C fixation (accA, aclB, acsA, rbcL), N fixation (nifH), and nitrification (amoA, hao) related genes. In the later restoration years, the microbial functional genes were dominant with labile C degradation (amyA, amyX, apu, sga, abfA), and denitrification (nosZ, nirS, narG, napA) related genes. The changes in microbial functional genes were mainly related to soil biotic factors (microbial biomass C and N, as well as C- and N-acquiring enzymes). Finally, we made a framework illustrating the changes in microbial eco-strategies and soil C, N cycling processes. This is the first attempt to link microbial functional genes with microbial eco-strategies by incorporating soil microbial meta-genomic information during grassland restoration.