Water addition promotes vegetation recovery of degraded alpine meadows by regulating soil enzyme activity and nutrients in the Qinghai-Tibetan Plateau

Effective grassland restoration practices can promote degraded meadows recovery. However, little has been documented regarding the effect of water addition on the restoration of degraded meadows in the Qinghai-Tibetan Plateau (QTP). A field experiment with five water addition levels was established to identify the interactions between soil bio-physicochemical properties and plant of the degraded alpine meadows in the Sanjiangyuan region, QTP. Soil enzyme activity (alpha-glucosidase, alpha G; beta-1,4-glucosidase, beta G; beta-D-cellubiosidase, beta DC; beta-xylosidase, beta X; beta-1,4-N-acetylgucosaminidase, NAG; leucine aminopeptidase, LAP; phosphorus, P), microbial biomass C (MBC) and N (MBN), MBC: MBN, physicochemical properties (soil moisture content, SMC; bulk density, SBD; pH; total organic C, TOC; total N, TN; soil C: N; ammoniacal N, NH4+-N; nitrate N, NO3--N; nitrite N, NO2--N), and plant diversity and productivity were analyzed throughout the growing season. The results indicated that soil SMC, available N (NH4+-N and NO3--N), TOC, the activities of alpha G, beta DC, beta X, NAG, MBC and MBN significantly increased with water addition levels, whereas the activity of LAP and P, and MBC: MBN decreased (p < 0.05). The redundancy analysis (RDA) and the subsequent path analysis found that soil biological (beta G, beta DC, beta X, NAG, LAP, MBC, and MBN) and physicochemical properties, especially TOC, NH4+-N, and NO3--N, were significantly related to plant diversity and productivity. The changes in soil enzyme activity (especially beta DC, beta G, LAP) under water addition might the key drivers affecting soil nutrients such as TOC, NO3--N and NH4+-N, which subsequently increased plant coverage and productivity. Our findings suggested that the obviously increase in enzymes activity and nutrients might be beneficial for the vegetation recovery of degraded alpine meadow on the QTP under water addition.