Soil organic matter (SOM) represents an important terrestrial carbon reservoir in the biosphere, and microorganisms have been recognized as significant material contributors to the formation of SOM. However, the turnover of microbial biomass residues with respect to their detailed microbial food web remains elusive. To elucidate this turnover process, we traced the fate of Gram-negative (Gram⁻) microbial biomass carbon through the microbial food web over time, using the concentrations and isotopic compositions of biomarker phospholipid fatty acids (PLFA) in a soil incubation with isotopically (¹³C) labelled model bacterial cells (Escherichia coli). We found that after 120 days 46.5% of the recovered E. coli derived ¹³C remained in the soil, whereas 53.5% was emitted as ¹³CO₂ (recovery 77.0% of the initially added ¹³C). The ¹³C in microbial biomass decreased to 5.3% of the initial value. This indicates that about 41% of the E. coli biomass in our experiment was transformed to SOM. The PLFA patterns over time demonstrate the pathway of ¹³C transformation associated with different groups of microorganisms along the incubation. The E. coli-derived ¹³C was utilized by fungi first, then the label was shifted from fungi to Gram-positive (Gram⁺) bacteria, arbuscular mycorrhizal fungi (AMF), actinomycetes, and to Gram⁻ bacteria other than E. coli. Finally the carbon was transferred from all consumers to the next consumer level; this is reflected in ongoing loss of ¹³C-PLFA without a shift in the ¹³C-PLFA pattern. In summary, our study details the turnover process of microbial biomass residues via the microbial food web to necromass and finally to SOM. This supports the soil microbial pump concept, i.e. carbon channelling and the assimilation of easily degradable carbon into microbial biomass and a significant contribution of these residues in SOM.

土壤有机物（SOM）代表着生物圈中重要的陆地碳储集层，微生物已被认为是SOM形成的重要物质贡献者。然而，微生物生物质残留物相对于其详细的微生物食物网的周转率仍然难以捉摸。为了阐明这个周转过程中，我们跟踪的革兰氏阴性（革兰氏的命运^- ）微生物生物量通过微食物网随着时间的推移碳，使用浓度和生物标志物的同位素组成磷脂脂肪酸（PLFA）在土壤培养与同位素（¹³ C）标记的模型细菌细胞（大肠杆菌）。我们发现120天后，有46.5％的回收大肠杆菌衍生了¹³C保留在土壤中，而53.5％的气体以¹³ CO _2的形式排放（回收的77.0％最初添加的¹³ C）。微生物生物量中的¹³ C降至初始值的5.3％。这表明在我们的实验中，约41％的大肠杆菌生物质转化为SOM。随着时间的流逝，PLFA模式证明了¹³ C转化的途径与孵育过程中不同种类的微生物有关。在大肠杆菌来源的¹³ C是通过真菌第一，则标签被从真菌转移到革兰氏阳性（革兰氏利用⁺）细菌，丛枝菌根真菌（AMF），放线菌，和革兰氏⁻大肠杆菌以外的细菌。最终，碳从所有消费者转移到了下一个消费者水平。这反映在¹³ C-PLFA的持续亏损中，而¹³ C-PLFA模式并未发生变化。总而言之，我们的研究详述了微生物生物质残留物通过微生物食物网到坏死，最后到SOM的周转过程。这支持了土壤微生物泵的概念，即碳通道化和易于降解的碳同化为微生物生物量，以及这些残留物在SOM中的重要作用。