During the last decade, a paradigmatic shift regarding which processes determine the persistence of soil organic matter (SOM) took place. The interaction between microbial decomposition and association of organic matter with the soil mineral matrix has been identified as a focal point for understanding the formation of stable SOM. Using an improved version of the vertically resolved SOM model COMISSION (Ahrens et al., 2015), this paper investigates the effect of a maximum sorption capacity (Q_max) for mineral-associated organic matter (MAOM) formation and its interaction with microbial processes, such as microbial decomposition and microbial necromass production.

We define and estimate the maximum sorption capacity Q_max with quantile regressions between mineral-associated organic carbon (MAOC) and the clay plus silt (<20 μm) content. In the COMISSION v2.0 model, plant- and microbial-derived dissolved organic matter (DOM) and dead microbial cell walls can sorb to mineral surfaces up to Q_max. MAOC can only be decomposed by microorganisms after desorption.

We calibrated the COMISSION v2.0 model with data from ten different sites with widely varying textures and Q_max values. COMISSION v2.0 was able to fit the MAOC and SOC depth profiles, as well as the respective ¹⁴C gradients with soil depth across these sites. Using the generic set of parameters retrieved in the multi-site calibration, we conducted model experiments to isolate the effects of varying Q_max, point-of-entry of litter inputs, and soil temperature. Across the ten sites, the combination of depolymerization limitation of microorganisms due to substrate scarcity in the subsoil and the size of Q_max explain ¹⁴C depth gradients in OC.

在过去的十年中，发生了关于哪些过程决定土壤有机质（SOM）持久性的范式转变。微生物分解和有机物与土壤矿质基质之间的相互作用之间的相互作用已被确定为了解稳定SOM形成的重点。本文使用垂直分辨SOM模型COMISSION的改进版本（Ahrens et al。，2015），研究了最大吸附容量（Q _max）对矿物相关有机物（MAOM）形成及其与微生物过程相互作用的影响，例如微生物分解和微生物坏死的产生。

我们用矿物相关有机碳（MAOC）和粘土加粉砂（<20μm）含量之间的分位数回归来定义和估计最大吸附容量Q _max。在COMISSION v2.0模型中，植物和微生物衍生的溶解有机物（DOM）和死微生物细胞壁可以吸附到矿物表面，_最大Q _max。解吸后，MAOC只能被微生物分解。

我们使用来自十个不同站点的数据校准了COMISSION v2.0模型，这些站点的纹理和Q_最大值变化很大。COMISSION v2.0能够拟合MAOC和SOC深度剖面，以及在这些站点上具有土壤深度的相应¹⁴ C梯度。使用在多站点校准中检索到的通用参数集，我们进行了模型实验，以隔离变化的Q _max，垃圾输入点和土壤温度的影响。在这十个站点中，由于土壤中底物稀缺和Q _max的大小导致的微生物解聚限制的组合解释了OC中¹⁴ C深度梯度。