Soil aggregates are critical to soil functionality, but there remain many uncertainties with respect to the role of biotic factors in forming aggregates. Understanding the interacting effects of soil, land use type, vegetation and microbial communities is a major challenge that needs assessment in both field and controlled laboratory conditions, as well as in bulk and rhizosphere soils. To address these effects and their feedbacks, we first examined the influence of soil, root and litter characteristics along a land use gradient (ancient woodland, secondary woodland, grassland, pasture and arable land) on microbial community structure (in both bulk and rhizosphere soil), as well as on aggregate stability. Then, we performed an inoculation experiment where we extracted soil columns from the arable and secondary woodland and used a third unstructured loamy soil as a control. We sterilized these three soils to remove microbial communities, and then inoculated the tops of sterilized soil columns with soil from the secondary woodland or the arable field sites. Control columns of all soil types were not inoculated. In a fully-crossed design, we planted two species possessing distinct root system morphologies: Brachypodium sylvaticum (fibrous system with many thin and fine roots) and Urtica dioica (taproot system with few fine roots). After four months, microbial communities (in bulk and rhizospheric soil) and aggregate stability were measured, along with root traits. In both the field and laboratory experiments, bacterial (16S) and fungal (ITS) diversity was determined using high throughput sequencing. In the field study we found that: i) there were strong relationships between aggregate stability and microbial community composition that were driven by land use, ii) the relationship between aggregate stability along the land use gradient and the trophic nature of bacterial communities was not significant, but certain soil, root and litter parameters shaped bacterial phyla, with oligotrophic bacteria conditioned by the rhizosphere niche, and copiotrophic phyla more dependent on bulk soil conditions, iii) land use gradient (from woodland to arable), reduced the relative abundance of saprotrophic and ectomycorrhizal fungi with an increase in the relative abundance of Ascomycota and a reduction in the relative abundance of Basidiomycota. In the laboratory experiment we found that: i) the inoculation of sterilized soils with soils from the field significantly increased aggregate stability in control soil that was initially poorly structured, ii) the effects of inoculation on aggregate stability were similar when either secondary woodland or arable soils were used as inoculums and iii) these effects were impacted significantly by root length density. Our results show that microbial communities influence soil structure and that bacterial communities are intimately associated to rhizospheric conditions and root traits (of which root length density was the most pertinent).

土壤聚集体对土壤功能至关重要，但就生物因子在形成聚集体中的作用而言，仍存在许多不确定性。理解土壤，土地利用类型，植被和微生物群落的相互作用是一项重大挑战，需要在野外和受控实验室条件以及块状和根际土壤中进行评估。为了解决这些影响及其反馈，我们首先研究了土地利用梯度（古代林地，次生林地，草地，牧场和耕地）上的土壤，根和凋落物特性对微生物群落结构（散装和根际土壤）的影响）以及总体稳定性。然后，我们进行了接种实验，从耕地和次生林地中提取土壤柱，并使用第三种非结构化壤土作为对照。我们对这三种土壤进行了灭菌处理，以去除微生物群落，然后用次生林地或耕地中的土壤接种了灭菌土壤柱的顶部。没有接种所有土壤类型的对照柱。在完全杂交的设计中，我们种植了两种具有独特根系形态的物种：短枝短螺旋藻（有许多薄而细的根的纤维系统）和荨麻（taproot系统具有很少的细根）。四个月后，测量了微生物群落（散装和根际土壤中）和团聚体的稳定性以及根系性状。在现场和实验室实验中，使用高通量测序确定了细菌（16S）和真菌（ITS）的多样性。在实地研究中，我们发现：i）土地利用驱动的聚集体稳定性与微生物群落组成之间存在很强的关系，ii）沿土地利用梯度的聚集体稳定性与细菌群落的营养性质之间的关系不显着，但某些土壤，根和凋落物参数塑造了细菌门，其根际生态位调节了贫营养细菌，而营养营养的门更依赖于整体土壤条件，iii）土地利用梯度（从林地到耕地），减少了腐生和外生菌根真菌的相对丰度，增加了子囊菌的相对丰度，减少了担子菌的相对丰度。在实验室实验中，我们发现：i）用田间土壤接种无菌土壤可显着提高最初结构较差的对照土壤的团聚体稳定性，ii）次生林地或耕地中接种对团聚体稳定性的影响相似土壤被用作接种物，并且iii）这些影响受到根长密度的显着影响。