Soil bacterial communities in grasslands revegetated using Elymus nutans are largely influenced by soil pH and total phosphorus across restoration time

Soil microbial communities have been considered indicators of soil quality and fertility changes in restored ecosystems. Little is known, however, about how these communities change over time after restoration in terms of activity, structure, and diversity. We evaluated the soil bacterial communities of 4-, 8-, and 12-year-old Elymus nutans revegetated grasslands located in the Qinghai-Tibetan Plateau. Soil bacterial diversity and composition significantly changed in the 8- and 12-year-old grasslands compared with the 4-year-old grassland. Surprisingly, soil bacterial communities transitioned from Proteobacteria- and Acidobacteria-dominant communities in the 4-year-old grassland to Cyanobacteria-dominant communities in the 8- and 12-year-old grasslands. Furthermore, the phylum of Cyanobacteria accounted for a high percentage of bacterial community (>48%) in the 8- and 12-year-old grasslands. Network analyses showed that most of the interactions were identified as positive among bacterial species, but Cyanobacteria were often negatively associated with other species. In addition, there was a slight increase in P acquisition enzymes (acid phosphatase activity) and a decline in N acquisition enzymes (soil urease and nitratase activities) with the increasing dominance of Cyanobacteria. Additionally, soil pH and total phosphorus had positive relationships with soil bacterial composition and diversity, whereas soil bacterial diversity and P acquisition enzymes were negatively related to soil bacterial composition. Overall, our results indicated that significant changes in soil bacterial communities might occur in response to the cultivation period of cultivated grassland and highlighted the importance of soil pH, TP, and P acquisition enzymes in microbe-mediated ecological processes of cultivated grassland on the Qinghai-Tibetan Plateau.