Miss Yue Cai1,2, Ms Tian Ma1,2, Miss Yiyun Wang1,2, Dr Juan Jia1, Dr Yufu Jia1, Dr Xiaojuan Feng1,2
1Institute Of Botany, Chinese Academy Of Sciences, Beijing, China, 2University of Chinese Academy of Sciences, Beijing, China
Soil microbes are known to play a key role in transforming labile organic carbon (OC) into relatively stable soil carbon in the form of microbial necromass. However, the efficiency of microbial necromass accumulation relative to labile OC mineralization remains under-investigated, which has vital implications for soil carbon sequestration. Here we construct artificial soils based on fructose, a common microbial inoculum and inorganic matrices with varying contents of clay and mineralogy to examine mineral regulations on microbial necromass accrual versus mineralization. By measuring microbial biomass and necromass (indicated by amino sugars) relative to respiration, we compare microbial carbon use efficiency (CUE) and amino sugar accumulation efficiency (AAE) throughout the 116-day incubation. We find that while clay promotes microbial consumption of labile OC (fructose), it enhances the rate as well as efficiency of microbial necromass accumulation without affecting CUE. On the contrary, ferrihydrite decreases CUE and AAE and promotes fructose preservation via inhibiting microbial growth. Hence, microbial necromass accrual is more efficient in clay-rich soils while labile OC is better preserved in soils containing ferrihydrite. Collectively, our findings suggest that the accrual efficiency of microbial carbon heavily depends on its preservation other than growth efficiency and is mediated by soil mineral content as well as composition. Parameters depicting microbial carbon preservation such as AAE warrant further study for modelling and managing the formation of microbial derived stable soil OC.
Yue Cai is a 5th-year Ph.D. student at the Institute of Botany, Chinese Academy of Sciences. She mainly investigates mineral and microbial effects on soil organic carbon sequestration. She has published one first-authored paper in the Journal of Geophysical Research: Biogeosciences and has another first-authored paper under review in Biogeochemistry.