Soil nitrogen availability regulates fungal necromass contribution to soil organic carbon during vegetation restoration

Abstract

Microbial necromass is an important component of soil organic carbon (SOC) and increases with vegetation restoration. Yet, the quantitative evaluation of the drivers of microbial necromass accumulation during restoration on large scales remains unclear. Here, a global meta-analysis of 462 paired peer studies (covering temperate, tropical, and subtropical zones) was firstly conducted to quantitatively evaluate the response of fungal vs. bacterial necromass contributions across restoration strategies. On average, vegetation restoration significantly increased microbial necromass C content by 67 % (95 % CIs: 56 %–79 %), with a greater increase of 115 % (95 % CIs: 97 %–134 %), 75 % (95 % CIs: 63 %–88 %), and 69 % (95 % CIs: 57 %–81 %) in natural restoration, forest soils, and >20 years restoration compared to artificial, grassland, and <20 years restoration, respectively. The constant contributions of microbial necromass to SOC were due to the offset of fungal (10 %) and bacterial necromass (−9 %) contributions to SOC. This observation implies the high consistency of SOC and microbial necromass, as well as the importance of fungal-dominated community in SOC sequestration. The restoration effects on microbial necromass and C sequestration were dominantly explained by soil C/N (nitrogen) as soil C/N > 15 enhanced microbial biomass (MB) conversion to necromass (ΔMNC/MB = 1.21), driving SOC sequestration. This indicates that vegetation restoration might be an efficient approach for microbial-derived C accumulation in N-limited soils (soil C/N > 15), such as ecologically vulnerable regions. Overall, this study indicates that long-term natural forest restoration is recommended for microbial necromass accumulation, and highlights the importance of soil N availability in improving soil microbial-derived C sequestration in response to global land use changes.