Environmental and Microbial Controls on Microbial Necromass Recycling, an Important Precursor for Soil Carbon Stabilization

There is an emerging consensus that microbial necromass carbon is the primary constituent of stable soil carbon, yet the controls on the stabilization process are unknown. Prior to stabilization, microbial necromass may be recycled by the microbial community. We propose that the efficiency of this recycling is a critical determinant of soil carbon stabilization rates. Here we explore the controls on necromass recycling efficiency in 27 UK grassland soils using stable isotope tracing and indicator species analysis. We found that recycling efficiency was unaffected by land management. Instead, recycling efficiency increased with microbial growth rate on necromass, and was highest in soils with low historical precipitation. We identified bacterial and fungal indicators of necromass recycling efficiency, which could be used to clarify soil carbon stabilization mechanisms. We conclude that environmental and microbial controls have a strong influence on necromass recycling, and suggest that this, in turn, influences soil carbon stabilization.