Stockbridge School of Agriculture and School of Earth & Sustainability, University of Massachusetts, Amherst, Massachusetts 01003, United States.
Department of Biology, Lund University, 223 62 Lund, Sweden.
Environ Sci Technol. 2021 Mar 2;55(5):3389-3398. doi: 10.1021/acs.est.0c04592. Epub 2021 Feb 15.
Most mineral-associated organic matter (MAOM) is protected against microbial attack, thereby contributing to long-term carbon storage in soils. However, the extent to which reactive compounds released by plants and microbes may destabilize MAOM and so enhance microbial access, as well as the underlying mechanisms, remain unclear. Here, we tested the ability of functionally distinct model exudates-ligands, reductants, and simple sugars-to promote microbial utilization of monomeric MAOM, bound via outer-sphere complexes to common iron and aluminum (hydr)oxide minerals. The strong ligand oxalic acid induced rapid MAOM mineralization, coinciding with greater sorption to and dissolution of minerals, suggestive of direct MAOM mobilization mechanisms. In contrast, the simple sugar glucose caused slower MAOM mineralization, but stimulated microbial activity and metabolite production, indicating an indirect microbially-mediated mechanism. Catechol, acting as reductant, promoted both mechanisms. While MAOM on ferrihydrite showed the greatest vulnerability to both direct and indirect mechanisms, MAOM on other (hydr)oxides was more susceptible to direct mechanisms. These findings suggest that MAOM persistence, and thus long-term carbon storage within a given soil, is not just a function of mineral reactivity but also depends on the capacity of plant roots and associated microbes to produce reactive compounds capable of triggering specific destabilization mechanisms.
大多数与矿物有关的有机质（MAOM）受到微生物攻击的保护，从而有助于土壤中碳的长期储存。然而，植物和微生物释放的反应性化合物可能使 MAOM 不稳定并增强微生物的可利用性的程度，以及潜在的机制，仍然不清楚。在这里，我们测试了功能不同的模型分泌物-配体、还原剂和简单糖-促进通过外球络合物与常见的铁和铝（氢）氧化物矿物结合的单体 MAOM 被微生物利用的能力。强配体草酸诱导 MAOM 迅速矿化，同时与矿物的吸附和解吸增加，表明存在直接的 MAOM 动员机制。相比之下，简单的糖葡萄糖导致 MAOM 矿化较慢，但刺激了微生物的活性和代谢产物的产生，表明存在间接的微生物介导的机制。儿茶酚作为还原剂，促进了这两种机制。虽然在水铁矿上的 MAOM 对直接和间接机制都表现出最大的脆弱性，但在其他（氢）氧化物上的 MAOM 更容易受到直接机制的影响。这些发现表明，MAOM 的持久性，以及因此在给定土壤中碳的长期储存，不仅取决于矿物的反应性，还取决于植物根系和相关微生物产生能够触发特定失稳机制的反应性化合物的能力。
