Restoration Measures of Fencing after Tilling Guided Succession of Grassland Soil Microbial Community Structure to Natural Grassland in the Sanjiangyuan Agro-pasture Ecotone of the Qinghai-Tibetan Plateau

In the fragile Sanjiangyuan (SJY) agro-pasture ecotone of the Qinghai-Tibetan Plateau (QTP), planting and fencing have been used to alleviate grassland degradation and to provide high-quality grass seeds for the implementation of the project of "grain for green". The soil microbe is the major driving factor in maintaining plant productivity and soil nutrient cycling. However, few studies have explored the effects of planting and fencing on soil microorganisms in the SJY agro-pasture ecotone. We explored the effects of tilling (TG) and fencing after tilling (FTG) on soil microbial communities to reveal the effects of restoration measures on soil microbes and to provide a reference in assessing and improving ecosystem structure. The results showed that restoration measures increased soil microbial species diversity and significantly changed their community structure. We found, the microbial composition was more complex under FTG, and its fungal variability was higher and more similar to that of natural grassland. Additionally, restoration measures resulted in fungal co-occurrence network was more edges, higher density, larger diameter and more positive interactions. This was due to the management of the vegetation-soil microenvironment by FTG inducing a differentiation of microbial community structure. In summary, the implementation of FTG could change the microenvironment in the SJY agro-pasture ecotone, so that variation in the structure of microbial community tended toward that of natural grassland, and increased the stability of microbial co-occurrence network, which was more obvious in the fungal community. HIGHLIGHTS: • Restoration measures have changed the vegetation characteristics and soil microenvironment. • Fencing after tilling (FTG) has brought the microenvironment closer to natural grassland. • FTG significantly increased microbial unique ASVs. The number of fungal unique ASVs was similar to that of natural grassland. • FTG resulted in changes in microbial community structure towards natural grasslands and increased the stability of the microbial co-occurrence network, which was more apparent in the fungal community.