The addition of organic carbon and nitrogen accelerates the restoration of soil system of degraded alpine grassland in Qinghai-Tibet Plateau

Abstract Soil degradation is often accompanied with the decrease of soil organic matter and soil fertility, and the direct addition of organic carbon and nitrogen could be the good method to accelerate the restoration of soil system of degraded grassland. The effects of the addition of biochar and nitrogen on soil properties and microorganisms in the 0-20 cm soil depth of degraded alpine grassland were evaluated. The treatments consisted of three different levels of biochar (1 kg m−2, 2 kg m−2, and 4 kg m−2) and nitrogen (5 g m−2, 10 g m−2, 15 g m−2). The addition of biochar and nitrogen increased soil organic carbon, total nitrogen, available phosphorus, water content (SWC), urease, phosphatase，and microbial biomass. The relative content of arbuscular mycorrhizal fungi, 18:1w9c fungi, actinomycetes, gram-negative and gram-positive bacteria increased, however, 18:2w6,9c fungi, anaerobic bacteria and methanotrophic bacteria decreased. Under the effect of biochar and nitrogen addition, most of soil physicochemical properties showed significant correlation in the 0-20 cm soil layer. The correlation between microbial community and soil properties mainly occurred in the 0–10 cm soil layer. The community of fungi, actinomycetes, gram-negative and Gram-positive bacteria showed significant relationship with soil urease, phosphatase, and available phosphorus (P   0.30). Arbuscular mycorrhizal fungi showed strong positive correlation with pH, NH4+, and SWC. These results indicated that the addition of biochar and nitrogen quickly improved soil nutrient and microbial community of degraded alpine grassland and could be used for the remediation of degraded alpine grassland.