Relative roles of niche and neutral processes on turnover of plant, fungal and bacterial communities in arid and semi-arid areas at the regional scale

Determining the contribution of microbiome complexity to the soil nutrient heterogeneity of fertile islands in a desert ecosystem

"Fertile islands" are known as hotspots of soil nutrient spatial heterogeneity in dryland ecosystems. Although soil microorganisms play critical functional roles in nutrient capture and cycling within fertile islands, our understanding of polymicrobial community roles in regulating soil nutrient distribution in fertile islands remains limited. Herein, we aim to clarify the relationships between the complexity of soil microbial (bacterial, archaeal and fungal) communities and the nutrient distribution around fertile islands. Soil samples were collected along vertical profiles at varying depths in three patches under the canopy of Hedysarum scoparium (CENTRE), at the edge (EDGE) of the canopy and outside (OUTSIDE) the canopy in an area of flowing sand. All the three microbiota have showed spatial heterogeneity around the fertile islands. Among them, bacteria had the most significant heterogeneity, and bacterial community assembly was dominated by deterministic processes. Microbial interaction patterns also showed spatial heterogeneity among different patches. More interaction complexity within microbiota was found in the bacteria in the CENTRE patch and in the fungi in the OUTSIDE patch. In addition, the proportions of among-kingdom connections were reduced under the canopies. Bacteria had the highest connectivity and centrality in the polymicrobial networks and were the most important predictor of polymicrobial interaction complexity, which may have contributed to the distribution of soil nutrients. The random forest (RF) model provided evidence that bacterial beta-diversity and the polymicrobial network complexity index can be optimal predictors of the soil multinutrient cycling index. Our study highlighted the responses of bacteria and polymicrobial interactions to fertile islands and their importance in driving soil nutrient heterogeneity. This information will help in managing soil microorganisms to provide dryland ecosystem services.

Ride the dust: Linking dust dispersal and spatial distribution of microorganisms across an arid landscape

In arid ecosystems, where the soil is directly exposed to the action of the wind due to sparse vegetation, dust aerosolization is a consequence of soil degradation and concomitantly, a major vector of microbial dispersal. Disturbances such as livestock grazing or fire can exacerbate wind erosion and dust production. Here, we sampled surface soils in 29 locations across an arid landscape in southwestern USA and characterized their prokaryotic and fungal communities. At four of these locations, we also sampled potential fugitive dust. By comparing the composition of soil and dust samples, we determined the role of dust dispersal in structuring the biogeography of soil microorganisms across the landscape. For Bacteria/Archaea, we found dust associated taxa to have on average, higher regional occupancies compared to soil associated taxa. Complementarily, we found dust samples to harbor a higher amount of widely distributed taxa compared to soil samples. Overall, our study shows how dust dispersal plays a role in the spatial distribution of soil Bacteria/Archaea, but not soil Fungi, and might inform indicators of soil health and stability in arid ecosystems. This article is protected by copyright. All rights reserved.

Characteristics and driving mechanisms of species beta diversity in desert plant communities

Species dissimilarity (beta diversity) primarily reflects the spatio–temporal changes in the species composition of a plant community. The correlations between β diversity and environmental factors and spatial distance can be used to explain the magnitudes of environmental filtering and dispersal. However, little is known about the relative roles and importance of neutral and niche-related factors in the assemblage of plant communities with different life forms in deserts. We found that in desert ecosystems, the β diversity of herbaceous plants was the highest, followed by that of shrubs and trees. The changes in the β diversity of herbs and shrubs had stronger correlations with the environment, indicating that community aggregation was strongly affected by niche processes. The soil water content and salt content were the key environmental factors affecting species distributions of the herb and shrub layers, respectively. Spatial distance explained a larger amount of the variation in tree composition, indicating that dispersal limitation was the main factor affecting the construction of the tree layer community. The results suggest that different life forms may determine the association between organisms and the environment. These findings suggest that the spatial patterns of plant community species in the Ebinur Lake desert ecosystem are the result of the combined effects of environmental filtering and dispersal limitation.