Edge effects and spatial degradation process in highly fragmented grassland-impact on soil microbial community

Patchy degradation is a typical characteristic of grassland degradation. However, little is known about the responses of soil microbial community composition and richness to patchy degradation process, although soil microbes play important roles in the functioning of terrestrial ecosystems. Further, there is always a transitional area of vegetation between non-degraded and degraded patches (i.e. ecotone), but the characteristics of soil microbial communities at ecotone are not well understood. Here, we investigated spatial patterns of soil microbial composition and richness from non-degraded to degraded patch in a patchy degraded grassland of Northern China. The results showed that bacterial and fungal richness had contrast patterns during patchy degradation process. Bacterial richness increased while fungal richness decreased from non-degraded to degraded patch. Notably, soil bacteria had significant edge effects, characterized by more abundant bacterial taxa at ecotone compared with non-degraded and degraded patches, which was attributable to the release of competition from the lower dominant phylum-Actinobacteria abundance. Moreover, the relative abundance of rare taxa for bacteria and fungi consistently decreased during patchy degradation process, indicating a reduction of ecosystem function. Relative abundance of soil microbial rare taxa could be a good ecological indicator in responding to grassland degradation. Overall, our study revealed the spatial patterns of soil microbial community during patchy degradation process and the microbial characteristics at ecotone, which is crucial for mechanistic understanding of grassland degradation process, and also providing a theoretical basis for the development of grassland restoration strategy.