Biology subjects

Simonsen, A. K.

Publications and source records attributed to Simonsen, A. K..

4 recordsLinked to original sources

bioRxiv2025

Hydrogenotrophic methanogenesis and distinct microbial assemblages fostered by dauciform roots of Cladium jamaicense

Nutrient availability regulates ecosystem processes, and plant roots strongly influence nutrient cycling through microbial interaction in the rhizosphere. In the extremely phosphorus-limited Florida Everglades, Cladium jamaicense (sawgrass) develops specialized roots, called dauciform roots, which release carboxylates that mobilize soil-bound nutrients. Although methanogenesis is a well-documented process in wetlands, the composition of methanogenic communities across separate root-associated compartments is not as well characterized. We investigated microbial community composition and predicted functional pathways across bulk soil, the general rhizosphere soil, and the rhizosphere of dauciform roots in calcareous (marl) soils near Everglades National Park. Functional predictions were inferred from 16SrRNA gene data using PICRUSt2 with taxonomic assignments referenced against SILVA v138.2 using rANOMALY. Alpha and beta community analyses revealed significant differences among compartments. Dauciform roots harbored the lowest Shannon diversity, whereas bulk soils supported the most distinct assemblages. Microbial communities clustered strongly by compartments, with compartment identity explaining 66% of the variation (p = 0.001). Pairwise comparisons showed the strongest separation between bulk and dauciform soils. Furthermore, functional predictions showed enrichment of hydrogenotrophic methanogenesis sequences in dauciform roots, while acetoclastic methanogenesis was most abundant in rhizosphere soils further emphasizing their distinct communities. Our preliminary results demonstrate that root-associated compartments foster distinct microbial assemblages with implications for key ecosystem processes, including methanogenesis. These findings highlight how root traits in oligotrophic systems influence carbon cycling and potential methane pathways, contributing to broader insights into microbial community assembly and ecosystem processes in nutrient-limited wetlands. HighlightsO_LIFirst genomic investigation of the dauciform root rhizosphere. C_LIO_LIRoot & dauciform rhizosphere harbor microbial communities distinct from bulk soil. C_LIO_LIPredicted enrichment of hydrogenotrophic methanogens in dauciform roots. C_LI

microbiology↗

bioRxiv2020

Priority effects alter interaction outcomes in a legume-rhizobium mutualism

Priority effects occur when the order of species arrival affects final community structure. Mutualists often interact with multiple partners in different orders, but if or how priority effects alter interaction outcomes is an open question. In the field, we paired the legume Medicago lupulina with two nodulating strains of Ensifer bacteria that vary in nitrogen-fixing ability. We inoculated plants with strains in different orders and measured interaction outcomes. The first strain to arrive primarily determined plant performance and final relative abundances of rhizobia on roots. Plants that received effective microbes first and ineffective microbes second grew larger than plants inoculated with the same microbes in opposite order. Our results show that mutualism outcomes can be influenced not just by partner identity, but by interaction order. Furthermore, hosts receiving high-quality mutualists early can better tolerate low-quality symbionts later, indicating priority effects may help explain the persistence of ineffective symbionts.

ecology↗

bioRxiv2018

More partners, more ranges: generalist legumes spread more easily around the globe

How does mutualism affect range expansion? On one hand, mutualists might thrive in new habitats thanks to the resources, stress tolerance, or defense provided by their partners. On the other, specialized mutualists might fail to find compatible partners beyond their range margins, limiting further spread. A recent global analysis of legume ranges found that non-symbiotic legumes have been successfully introduced to more ranges than legumes that form symbioses with rhizobia, but there is still abundant unexplained variation in introduction success within symbiotic legumes. Here, we test the hypothesis that generalist legumes have spread to more introduced ranges than specialist legumes. We used published data and rhizobial 16S rRNA sequences from GenBank to quantify the number of rhizobia partners that associate with each of 159 legume species, spanning the legume phylogeny and the globe. We found that generalist legumes occur in more introduced ranges than specialist legumes, suggesting that among mutualists, specialization hinders range expansions.

ecology↗

bioRxiv2018

Larger legume plants host a greater diversity of symbiotic nitrogen-fixing bacteria

A major goal in microbial ecology is to understand the factors that structure bacterial communities across space and time. For microbes that have symbiotic relationships with plants, an important factor that may influence their communities is host size or age, yet this has received little attention.\n\nUsing tree diameter size as a proxy for age, we quantified the diversity of rhizobia that associate with an endemic legume, Acacia acuminata, of variable size across a climate gradient in southwest Australia. We examined the 16S rRNA diversity (V1-V3 hypervariable region) of rhizobia at the taxonomic level and at higher sequence level diversity within taxonomic groups.\n\nWe identified 3 major taxonomic clades that associated with Acacia acuminata: Bradyrhizobiaceae, Rhizobiaceae, and Burkholderiaceae. Within these groups, we found extensive genetic variability, especially within Bradyrhizobiaceae. Using binomial multivariate statistical models that controlled for other factors that affect plant size and rhizobia community structure (climate and local soil characteristics), we determined that soil sampled at the base of larger Acacia trees was much more likely to contain a greater number of taxonomic clades and cryptic genetic variants within the Rhizobiaceae clade.\n\nDespite strong influences of climate and highly heterogeneous soil conditions on rhizobial diversity, our results show that host tree size is a prominent factor in structuring nitrogen-fixing symbionts diversity across a large landscape. The identification of a positive relationship between plant host size and microbial diversity raise interesting questions about the role of plant host size in driving ecological processes that govern microbial community assembly. Specifically, our results suggest that hosts may modify the habitat of their surrounding soil to enhance growth (niche construction hypothesis) or that symbiotic microbes have large differences in dispersal capability. Our results also suggest that host plants may be analogous to islands, where larger legume hosts may accumulate diversity over time, through migration opportunities or in situ diversification. From a practical perspective, including plant size as an additional variable may assist sampling and analyses designs of future soil microbial studies.

ecology↗