Substrate and community regulations on microbial necromass accumulation from newly added and native soil carbon

Microbial necromass accrual via anabolism is an important process contributing to the formation and accumulation of stable soil organic C (SOC). Both substrates and microbial community traits impact the rate and efficiency of microbial biomass production, yet their effects on necromass accumulation patterns and efficiency remain unclear. Here we selected six substrates to investigate substrate and community regulations on microbial necromass accumulation over a 476-day model soil incubation including three stages (microbial growth-starvation-reactivation) with varied supply of substrates or C-13-labeled glucose. Microbial respiration, the composition of main microbial groups, and necromass (amino sugars) production were examined along with C-13 analysis to compare necromass accumulation from new OC and native SOC. We found that relative to fast-decomposing substrates, slow-decomposing substrate like lignin induced slow but steady necromass accrual in a long term. Exogenous glucose input stimulated necromass accumulation from new and native SOC during reactivation, especially in C (or energy)-limited model soils. Furthermore, the accumulation efficiency of amino sugars sourced from SOC and C-13-labeled glucose were positively related, suggesting microbial communities and soil properties affect necromass accrual efficiency. However, there was quite some scatter in the correlation, suggesting potential substrate effect and uncertainty in this relationship. Hence, the efficiency of soil microbial C pump (i.e., microbial transformation of exogenous substrates into microbial byproducts) fueled by exogenous substrate and native SOC needs to be further investigated. Collectively, these findings provide new information on the dynamics and efficiency of microbial necromass accumulation from different substrates in soils.

Automated summary

Microbial necromass accrual via anabolism is an important process contributing to the formation and accumulation of stable soil organic C (SOC). Both substrates and microbial community traits impact the rate and efficiency of microbial biomass production, yet their effects on necromass accumulation patterns and efficiency remain unclear.