Abstract
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.
Highlights
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
Historic focus on plant input quantity and quality as key controls on soil C storage has only recently shifted in recognition that plant C assimilation into microbial biomass is an important precursor to soil C stabilization[2,3]
Our carbon use efficiency (CUE)-assays on grassland soils across a broad range of historical Land use intensity (LUI) (Fig. 2b) did not support the hypothesis that LUI was associated with microbial CUE
Summary
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. Historic focus on plant input quantity and quality as key controls on soil C storage has only recently shifted in recognition that plant C assimilation into microbial biomass is an important precursor to soil C stabilization[2,3]. We know that soil microbes assimilate plant C inputs for growth, and release C as extracellular products and CO2 (Fig. 1A): the balance of this anabolism and catabolism is microbial carbon use efficiency (CUE). We hypothesized that soil disturbance in high LUI sites (i.e., with tillage, grazing, and fertilization) would select for rapid growth microbes (i.e., “r-selected”) adapted to use labile substrates such as root exudates, and that this would result in higher CUE9,18. Identify those microbes associated with high necromass recycling efficiency To address these aims, we selected nine UK agricultural grassland farms (Fig. 2a) along precipitation, temperature, soil pH, and soil C gradients We used stable isotope probing of microbial phospholipids and statistical analyses of 16S- and ITSsequenced community data to identify microbial guilds, that dominate glucose and necromass uptake and recycling
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
