Variations and controls of soil microbial necromass carbon in grasslands along aridity gradients

Abstract

Microbial necromass is supposed to play fundamental role in contributing to soil organic carbon (SOC) stabilization, while variations and controls of grassland soil microbial necromass carbon (MNC) accumulation along aridity gradients remains unclear. In this study, we obtained data for 201 MNC concentrations in grasslands, and divided them into four categories according to aridity for further synthesized data analysis, i.e., humid, dry sub-humid, semi-arid and arid zones. Results showed that soil MNC was an essential contributor to SOC in grasslands, accounting for 47% to 66% of the SOC contents with the highest proportion in dry sub-humid zones compared with humid, semi-arid and arid zones. Bacterial necromass carbon (BNC) contributed more to SOC than fungal necromass carbon (FNC) for semi-arid zones, while FNC was more important in other climate zones. As for contributions of necromass carbon to SOC, soil pH and textures played more important roles in semi-arid and arid zones than climate did, while climate mattered in humid and dry sub-humid zones. Structural equation modelling analysis indicated that soil pH not only had a direct negative effect on soil FNC but also indirectly affected soil BNC by altering SOC. Mean annual temperature and soil C:N could also significantly affect soil FNC, BNC and MNC by regulating SOC and pH. Our results highlighted that aridity shifts may cause divergent impacts on MNC and the proportion of necromass carbon to SOC in grasslands with varied soil environments.