Abstract
In natural plant populations, a fine-scale spatial genetic structure (SGS) can result from limited gene flow, selection pressures or spatial autocorrelation. However, limited gene flow is considered the predominant determinant in the establishment of SGS. With limited dispersal ability of bacterial cells in soil and host influence on their variety and abundance, spatial autocorrelation of bacterial communities associated with plants is expected. For this study, we collected genetic data from legume host plants, Chamaecrista fasciculata, their Bradyrhizobium symbionts and rhizosphere free-living bacteria at a small spatial scale to evaluate the extent to which symbiotic partners will have similar SGS and to understand how plant hosts choose among nodulating symbionts. We found SGS across all sampled plants for both the host plants and nodulating rhizobia, suggesting that both organisms are influenced by similar mechanisms structuring genetic diversity or shared habitat preferences by both plants and microbes. We also found that plant genetic identity and geographic distance might serve as predictors of nodulating rhizobia genetic identity. Bradyrhizobium elkanii was the only type of rhizobia found in nodules, which suggests some level of selection by the host plant.
Highlights
Several studies have recognized plants as one of the most important factors shaping soil microbial community structure [1,2,3,4]
While a literature review found no fine-scale studies of genetic structure in nodulating rhizobia or plant endophytes for comparison to our results, we have found that the number of haplotypes recovered for C. fasciculata is similar to studies of other legumes
No study to date has been conducted on genetic diversity and structure of legume rhizobia system within Chamaecrista fasciculata and at the fine scale studied here
Summary
Several studies have recognized plants as one of the most important factors shaping soil microbial community structure [1,2,3,4]. It has been suggested that this may be the result of active selection by plants for certain soil microbes or shared habitat preferences by plants and microbes [5] because spatially close biological communities are more similar than expected by chance and this similarity decays with distance [6]. It has been demonstrated that differences in microbial community composition are significantly correlated with phylogenetic distance of their plant hosts [7]. Plants within a closely related taxonomic group are likely to share traits, including amount and availability of rhizodeposits and root defensive strategies, and these are key factors shaping soil microbial communities [10]. Plant hosts with similar genotypes may have similar soil microbial communities [1,11,12] which may indicate the presence of genotype x genotype interactions in these situations
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