Minerals and their interactions with dissolved organic matter as regulators of microbial necromass stabilization in soil

微生物坏死体被认为对稳定土壤有机质有重要贡献。然而，所谓的“埋葬效应”，即死亡团衍生物质的堆积和随后的稳定，在机制层面上仍然没有得到很好的理解。溶解有机物在活性矿物表面的吸附是土壤碳稳定的主要过程。因此，我们计划(I)研究从植物凋落物到微生物坏死体的分解连续体中溶解有机物的产生和反应性(生物降解性和吸附能力)，以及(Ii)同时研究有机化合物的吸附稳定化如何塑造微生物群落的结构及其碳和能量的利用。该项目将首次在对物质和能量通量进行定量评估的基础上，描述坏死体形成和溶解有机物吸收之间的相互作用。因此，它将有助于SPP 2322的中心假设C(边界条件)和B(生物复杂性)。拟议的研究将直接就地分解植物凋落物和微生物坏死体与深入分析潜在过程以确定坏死体稳定的所有步骤联系起来。这包括：(I)分解植物凋落物和微生物坏死体(细菌和真菌)产生溶解有机质的培养实验，(Ii)使用不同原始矿物的吸附实验，(Iii)溶解有机物在吸附之前/之后的生物降解性测试，(Iv)矿物结合有机质的稳定性测试，以及(V)天然土壤中碳标记的植物凋落物和微生物坏死体的培养。这种循序渐进的实验方法能够量化和解释不同有机来源到矿物表面的碳和能量转移效率的差异。测定溶解和吸附的有机物的分子组成和能量含量，以及使用最先进的方法，如FT-ICR-MS和XPS等对微生物群落进行分析，有助于对土壤中坏死体稳定的机制有新的见解。该项目将加深我们对矿物如何调节微生物能量利用的理解，从而有助于开发新一代土壤碳模型，明确表示微生物周转。

Microbial necromass is presumed to significantly contribute to stable soil organic matter. Yet, the so-called ‘entombing effect’, i.e. the built-up and subsequent stabilization of necromass-derived matter, is still not well understood on a mechanistic level. The sorption of dissolved organic matter to reactive mineral surfaces is widely known as a major process of soil carbon stabilization. Herein, we thus plan (i) to study production and reactivity (biodegradability and sorptivity) of dissolved organic matter along the decomposition continuum from plant litter to microbial necromass, and (ii) to concurrently examine how sorptive stabilization of organic compounds shapes the structure of the microbial community, and its carbon and energy use. The project will, for the first time, describe interactions between necromass formation and dissolved organic matter sorption on basis of a quantitative assessment of matter and energy fluxes. It will, therefore, contribute to Central Hypotheses C (Boundary conditions) and also B (Biological complexity) of the SPP 2322. The proposed research links direct in situ decomposition of plant litter and microbial necromass with in-depth analyses of underlying processes to identify all steps of necromass stabilization. This includes: (i) incubation experiments on the production of dissolved organic matter from decomposing plant litter and microbial necromass (bacteria and fungi), (ii) sorption experiments using different pristine minerals, (iii) biodegradability tests for dissolved organic matter before/after sorption, (iv) tests of the stability of mineral-bound organic matter, and (v) incubations of carbon-labelled plant litter and microbial necromass in natural soil. This step-wise experimental approach enables to quantify and explain differences in the transfer efficiency of carbon and energy from variable organic sources to mineral surfaces. The determination of the molecular composition and energy content of dissolved and sorbed organic matter as well as the analysis of the microbial community using state-of-the-art methods, such as FT-ICR-MS and XPS among others, allow for gaining novel insight into the mechanisms of necromass stabilization in soil. The project will add to our understanding how minerals regulate microbial energy use, and thus, contribute to the development of new-generation soil carbon models with explicit representation of microbial turnover.