Abstract. Particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), which are two primary components of the soil carbon (C) reservoir, have different physical and chemical properties as well as biochemical turnover rates. Microbial necromass entombment is a primary mechanism for MAOC formation from fast-decaying plant substrates, whereas POC is typically considered the product of structural litter via physical fragmentation. However, emerging evidence shows that microbial by-products derived from labile C substrates can enter the POC pool. To date, it is still unclear to what extent dissolved C can enter the POC pool and how it affects the subsequent long-term soil organic carbon (SOC) storage. Our study here, through a 13C-labeling experiment in 10 soils from 5 grassland sites as well as a modeling analysis, showed that up to 12.29 % of isotope-labeled glucose C (i.e., dissolved C) was detected in the POC pool. In addition, the glucose-derived POC was correlated with 13C-MBC (microbial biomass carbon) and the fraction of clay and silt, suggesting that the flow of dissolved C to POC is dependent on interactions between soil physical and microbial processes. The modeling analysis showed that ignoring the C flow from MBC to POC significantly underestimated soil C sequestration by up to 53.52 % across the 10 soils. The results emphasize that the soil mineral-regulated microbial process, besides the plant structural residues, is a significant contributor to POC, acting as a vital component in SOC dynamics.

中文翻译：

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溶解碳流向颗粒有机碳增强土壤固碳


摘要。颗粒有机碳（POC）和矿物伴生有机碳（MAOC）是土壤碳（C）库的两个主要组成部分，具有不同的物理和化学性质以及生化周转率。微生物坏死物埋葬是快速腐烂的植物基质形成 MAOC 的主要机制，而 POC 通常被认为是结构垃圾通过物理破碎的产物。然而，新出现的证据表明，源自不稳定 C 底物的微生物副产物可以进入 POC 池。迄今为止，尚不清楚溶解的碳在多大程度上可以进入POC库以及它如何影响随后的长期土壤有机碳（SOC）储存。我们的研究通过对 5 个草原地点的 10 种土壤进行 13C 标记实验以及建模分析，表明在 POC 池中检测到高达 12.29% 的同位素标记葡萄糖 C（即溶解 C）。此外，葡萄糖衍生的 POC 与 13C-MBC（微生物生物质碳）以及粘土和淤泥的比例相关，表明溶解的 C 向 POC 的流动取决于土壤物理和微生物过程之间的相互作用。模型分析表明，忽略从 MBC 到 POC 的碳流，会显着低估 10 种土壤的土壤碳固存量，高达 53.52%。结果强调，除了植物结构残留物之外，土壤矿物质调节的微生物过程也是 POC 的重要贡献者，是 SOC 动态的重要组成部分。