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Dust provides an ecologically significant input of nutrients, especially in slowly eroding ecosystems where chemical weathering intensity limits nutrient inputs from underlying bedrock. In addition to nutrient inputs, incoming dust is a vector for dispersing dust-associated microorganisms. While little is known about dust-microbial dispersal, dust deposits may have transformative effects on ecosystems far from where the dust was emitted. Using molecular analyses, we examined spatiotemporal variation in incoming dust microbiomes along an elevational gradient within the Sierra Nevada of California. We sampled throughout two dry seasons and found that dust microbiomes differed by elevation across two summer dry seasons (2014 and 2015), which corresponded to competing droughts in dust source areas. Dust microbial taxa richness decreased with elevation and was inversely proportional to dust heterogeneity. Likewise, dust phosphorus content increased with elevation. At lower elevations, early season dust microbiomes were more diverse than those found later in the year. The relative abundances of microbial groups shifted during the summer dry season. Furthermore, mutualistic fungal diversity increased with elevation, which may have corresponded with the biogeography of their plant hosts. Although dust fungal pathogen diversity was equivalent across elevations, elevation and sampling month interactions for the relative abundance, diversity, and richness of fungal pathogens suggest that these pathogens differed temporally across elevations, with potential implications for humans and wildlife. This study shows that landscape topography and droughts in source locations may alter the composition and diversity of ecologically relevant dust-associated microorganisms.

The rapidly increasing global population and anthropogenic climate change have created intense pressure on agricultural systems to produce increasingly more food under steadily challenging environmental conditions. Simultaneously, industrial agriculture is negatively affecting natural and agricultural ecosystems because of intensive irrigation and fertilization to fully utilize the potential of high-yielding cultivars. Growth-promoting microbes that increase stress tolerance and crop yield could be a useful tool for helping mitigate these problems. We investigated if commercially grown almonds might be a resource for plant colonizing bacteria with growth promotional traits that could be used to foster more productive and sustainable agricultural ecosystems. We isolated an endophytic bacterium from almond leaves that promotes growth of the model plant Arabidopsis thaliana. Genome sequencing revealed a novel Erwinia gerundensis strain (A4) that exhibits the ability to increase access to plant nutrients and to produce the stress-mitigating polyamine spermidine. Because E. gerundensis is known to be able to colonize diverse plant species including cereals and fruit trees, A4 may have the potential to be applied to a wide variety of crop systems.

While individual tree genotypes are known to differ in their impacts on local soil development, the spatial genetic influence of surrounding neighboring trees is largely unknown. We examine the hypothesis that fine root dynamics of a focal tree is based on the genetics of the focal tree as well as the genetics of neighbor trees that together define litter inputs to soils of the focal tree. We used a common garden environment with clonal replicates of individual tree genotypes to analyze fine root production, turnover and allocation with respect to modeled neighborhood: (1) foliar mass, (2) foliar condensed tannins (CT), (3) genetic identity of trees, and (4) genetic dissimilarity of neighbors. In support of our central hypothesis, we found that the presence of genetically dissimilar trees and high leaf CT contributions to the soil predicted increased fine root production. In fact, the modeled effects of neighbors accounted for ~90% of the explanatory weight of all models predicting root production. Nevertheless, the ultimate fate of those roots in soil (turnover) and the balance of fine roots relative to aboveground tree mass were still more predictable based on the leaf traits and genetics of the individual focal trees (explaining 99% of the variation accounted for by models). Our data provide support for a method allowing a comparison of the relative effects of individuals vs. spatial neighborhood effects on soils in a genetic context. Such comparisons are important for placing plant-soil feedbacks in a genetic and evolutionary framework because neighbors can decouple feedbacks between an individual and the surrounding environment.