The interaction between mineral particles and soil organic matter (SOM) is an important and complex process during soil structure formation, in which the effects of soil texture and OM properties are intertwined. Within the SOM, there are residues of particulate organic matter (POM) of various sizes, as well as microbial necromass co-existing. These OM residues undergo microbial decay whose products stabilize particle connections and thus induce aggregate formation.

We developed an experimental set-up to study early soil structure formation within a controlled lab environment. Artificial soil microcosms with a mineral mixture of different textures (clay loam, loam, and sandy loam) were used to perform a short-term incubation for 30 days under constant water tension. OM was added individually either as POM of two different size classes (milled hay litter, 0.63–2 mm and <63 µm, respectively) or bacterial necromass (Bacillus subtilis).

The dry mixing process and incubation of the mineral mixtures led to particle–particle interactions and fine particle coatings of the sand grains as shown by a reduction in the specific surface area (N₂-BET). The OM residues were quickly accessed and degraded by microbes (peak in CO₂-release within the first 10 days of incubation), which induced the formation of water-stable aggregates. The POM of both sizes induced predominantly the formation of macroaggregates (0.63–30 mm) with a mass contribution of 72% to 91%, irrespective of the mixtures’ texture. The bacterial necromass induced a texture-dependent formation of macro- and microaggregates (63–200 µm), with larger aggregates in sand-rich mixtures. The different aggregate sizes were related to differences in the developed microbial community, as obtained by PLFA analysis. The bacterial necromass induced a microbial community dominated by bacteria, whereas the POM fostered a high relative abundance of fungi, whose hyphae could enmesh and stabilize large aggregates in all textures.

The formed aggregates are water-stable but have a very low mechanical stability. Dry crushing with a mechanical loading frame revealed that very low forces (<4 N) were sufficient for breaking the aggregates down. Microbial growth and degradation of the OM residues led to OM patches occupying <17% of the mineral surfaces after the incubation, suggesting that the aggregates are loosely connected structures, bound together by some distinct spots of processed OM acting as gluing joints. This initially formed scaffold holds particles in place for further stabilization processes and resists immersion in water but exhibits no stability toward mechanical forces.

矿物颗粒与土壤有机质（SOM）之间的相互作用是土壤结构形成过程中一个重要而复杂的过程，其中土壤质地和OM特性的影响相互交织。在SOM中，存在各种大小的颗粒有机物（POM）残留物，以及微生物坏死共存。这些OM残留物会发生微生物衰变，其产物会稳定颗粒之间的连接，从而诱导聚集体的形成。

我们开发了一个实验装置，以研究在受控实验室环境中早期土壤结构的形成。使用具有不同质地的矿物混合物（粘土壤土，壤土和沙质壤土）的人工土壤微观世界，在恒定的水压下进行30天的短期培养。OM分别作为两种不同大小级别的POM（碾碎的干草，分别为0.63–2 mm和<63 µm）或细菌性坏死菌（枯草芽孢杆菌）添加。

干混过程和矿物混合物的孵育导致了沙粒的颗粒间相互作用和细颗粒涂层，如比表面积（N ₂ -BET）减小所显示。OM残留物可快速进入并被微生物降解（在CO _2中达到峰值）（在孵育的前10天内释放），诱导形成水稳定的聚集体。两种尺寸的POM都主要引起大聚集体（0.63–30 mm）的形成，其质量贡献为72％至91％，与混合物的质地无关。细菌坏死诱导了宏观和微观聚集体（63-200 µm）的纹理依赖性形成，富沙混合物中聚集体较大。通过PLFA分析得出，不同的聚集体大小与发达的微生物群落的差异有关。细菌坏死菌诱导了一个以细菌为主导的微生物群落，而POM则促进了相对较高的真菌含量，其菌丝可以融合并稳定所有质地的大聚集体。

所形成的聚集体是水稳定的，但是具有非常低的机械稳定性。用机械负载架进行干式破碎表明，极低的力（<4 N）足以将聚集体分解。孵育后，微生物残留物的微生物生长和降解导致OM斑块占据了矿物表面的<17％，这表明聚集体是松散连接的结构，由加工过的OM的一些不同点结合在一起，这些点充当胶合接头。这种最初形成的支架将颗粒固定在适当的位置，以进行进一步的稳定化处理，并防止浸入水中，但对机械力没有稳定性。