[Effects of Microbial Inoculants and Sheep Manure on Soil and Bacterial Diversity in a Degraded Alpine Meadow]

The Sanjiangyuan Region is an important ecological barrier in China. However， its alpine meadows have undergone intensified degradation due to climate warming and drying and human activities. Green and sustainable measures are urgently needed to restore the degraded meadow soil. A common measure for restoration is the use of fertilizers； however， the effects of bacterial fertilizer and manure on the physical and chemical properties of alpine meadow soil and rhizosphere bacterial communities have not yet been elucidated. To fill this knowledge gap， we analyzed the changes in soil bacteria and soil physical and chemical properties， evaluated the remediation effects of bacterial fertilizer in combination with manure on a moderately degraded alpine meadow in the Sanjiangyuan Region of the Yellow River， and screened for a suitable fertilization scheme to restore the alpine meadows via high-throughput sequencing technology. The results showed that：① The contents of soil water， organic matter， total nitrogen， total phosphorus， and inorganic nitrogen all increased significantly after fertilization with both bacterial fertilizer and sheep manure. The Y1K2 （sheep manure： 1 500 kg·hm^-2， bacterial fertilizer： 500 kg·hm^-2）， Y2K1 （sheep manure： 3 000 kg·hm^-2， bacterial fertilizer： 250 kg·hm^-2）， and Y3K1 （sheep manure： 6 000 kg·hm^-2， bacterial fertilizer： 250 kg·hm^-2） treatments all had significant effects on soil water content and nutrient content. ② In all 12 fertilization treatments， 19 341 bacterial species were detected， and bacterial communities at the phylum level were dominated by Actinobacteriota， Proteobacteria， and Acidobacteriota. Of these treatments， Y3K1 had the highest number of endemic bacteria at 885 species. ③ Fertilization appropriately increased the number of OTU， Shannon index， Ace index， Chao1 index， and Pielou index of the soil bacterial communities， but noticeably decreased the Simpson index. ④ Topologically， the soil bacterial network was characterized by increased complexity after nutrient supplementation， and the network was mainly positively correlated. It had the largest number of edges （1 106） in the Y0K2 treatment（sheep manure： 0 kg·hm^-2， bacterial fertilizer： 500 kg·hm^-2）. ⑤ A significant correlation existed between bacterial community structure and soil electrical conductivity （SEC） in all treatments （P<0.05）. The first and second axes reached 55.37% and 2.47%， respectively， in explaining the variations in soil bacterial community structure， plant community characteristics， and soil physical and chemical characteristics. SEC was identified as the key factor driving rhizosphere bacterial communities in the degraded alpine meadow. ⑥ According to the function prediction results， the bacterial communities had obvious advantages in aerobic heterotrophic and chemoheterotrophic functions. Thus， bacterial fertilizer in combination with sheep manure improved soil fertility and soil bacterial diversity， with the Y2K1 treatment being the most effective. Namely， a dosage of 3 000 kg sheep manure in combination with 250 kg bacterial fertilizer per hectare achieved the best restoration outcome.