In the past years, extracellular polymeric substances (EPS) produced by soil microorganisms received an increasing interest, as they not only protect microbes against environmental stresses, but seem to play a pivotal role in soil structure formation as well. Within soils, root deposits provide an important source of easily accessible energy and nutrients, stimulating microbial growth to produce EPS. Especially under semiarid climates, where a full vegetation cover cannot be sustained, large gradients in living conditions for microbes can be found between the root-soil interface and barren intercanopy spaces.

In this study, we aimed to elucidate the plant-specific effects on microbes, EPS production and soil aggregation. At two sites in southern Spain, differing in carbonate and graphite content, legume shrubs of Anthyllis cytisoides and grass tussocks of Macrochloa tenacissima were selected. Soil samples were taken in the adjacent bare interspace, under the canopy and of the rhizosphere. From these samples the microbial community (here bacteria and archaea), EPS(-saccharide) content and soil aggregation (<1 mm) were analysed. DNA extracted from the microbial cells detached from the surface of the sampled roots (rhizoplane), was subjected to 16S rRNA gene amplicon sequencing.

The rhizoplane microbial communities differed strongly between plant species and sites, whereby site was the most important factor shaping the communities. The plant species effect on microbial communities diminished strongly with distance to the root surface. At the carbonate-poor Rambla Honda site (site 1), plant species-specific effects were observed in the rhizoplane and rhizosphere, whereas in the carbonate-rich Alboloduy site (site 2) almost no plant species-specific effects were found at the genus level. The larger heterogeneity in microbial communities at site 1 was reflected in EPS-saccharide contents and subsequent soil aggregation, while no difference in soil aggregation was found at site 2. Both parameters increased strongest in the Anthyllis cytisoides rhizosphere at site 1.

Despite the lack of a strong gradient with distance from the root at the carbonate-rich site 2, microbial taxa were found by network analysis that positively correlated to EPS-saccharide contents and/or soil aggregation. The relationship between the identified taxa and EPS and/or aggregation relationships were clearest at the root-soil interface, while several other taxa were found to be widely occurring in the other soil compartments too.

In conclusion, we found in all compartments potential EPS producers, which could have influenced soil aggregation. Nevertheless, microbes with higher relative abundance in the rhizoplane were linked to higher EPS contents, especially in conjunction with legume shrubs, and subsequently related to soil aggregation. The spatial extent of the root effect was only governed by carbonate contents, as higher carbonate content diminished the observed root effects on the microbial community and subsequent soil aggregation.

在过去的几年中，土壤微生物产生的细胞外聚合物（EPS）受到越来越多的关注，因为它们不仅可以保护微生物免受环境压力的影响，而且在土壤结构的形成中也起着举足轻重的作用。在土壤中，根部沉积物提供了易于获取的能量和养分的重要来源，刺激了微生物的生长，从而产生了EPS。特别是在半干旱气候下，无法维持完整的植被覆盖，在根-土界面与贫瘠的冠层间空间之间会发现微生物的生存条件存在较大的梯度。

在这项研究中，我们旨在阐明植物对微生物，EPS产生和土壤聚集的特定影响。在西班牙南部的两个站点，在碳酸盐和石墨含量不同，豆科灌木Anthyllis cytisoides和草草丛Macrochloa藤选择。在邻近的裸露空间，冠层和根际下采集土壤样品。从这些样品中分析了微生物群落（这里是细菌和古细菌），EPS（糖）含量和土壤聚集（<1 mm）。从与采样根表面（根状平面）分离的微生物细胞中提取的DNA进行16S rRNA基因扩增子测序。

根际平面上的微生物群落在植物物种和部位之间差异很大，其中部位是影响群落的最重要因素。植物物种对微生物群落的影响随着与根表面距离的增加而大大降低。在碳酸盐含量低的兰布拉本田站点（站点1），在根际平面和根际中观察到了植物物种特异性的影响，而在富含碳酸盐的Alboloduy站点（站点2）中，几乎没有发现植物物种特异性的影响。等级。站点1的微生物群落中较大的异质性反映在EPS糖含量和随后的土壤聚集上，而站点2上没有发现土壤聚集的差异。站点1的Cytisoides Cytisoides根际中两个参数的增加最强。

尽管在富含碳酸盐的部位2上与根的距离缺乏强梯度，但通过网络分析发现微生物分类群与EPS糖含量和/或土壤聚集呈正相关。在根-土界面处，已识别的分类群与EPS和/或聚集关系之间的关系最清晰，而其他几个分类群也广泛分布在其他土壤隔室中。

总之，我们发现在所有隔间中都有潜在的EPS生产者，它们可能影响了土壤的聚集。然而，根际平面中相对丰度较高的微生物与较高的​​EPS含量相关，尤其是与豆科灌木结合使用时，随后与土壤聚集有关。根系效应的空间范围仅由碳酸盐含量决定，因为较高的碳酸盐含量会减少对微生物群落和随后土壤团聚的观察到的根系效应。