Role of Dispersal Limitation in Fungal Community Assembly
Due to their small size and rapid generation times, microbial communities were broadly believed to assemble swiftly in the absence of geographic or biological barriers to dispersal. Yet, mounting evidence indicates that dispersal limitation may shape microbial community assembly. Combining the study of microbial biogeography with functional trait analyses holds promise to increasing our mechanistic understanding of the environmental drivers of ecosystem-level processes, as well as the ecological forces structuring soil microbial communities.
Glacial retreat of the Wisconsin glacier ca. 14,000 years ago presents a unique opportunity to study the factors that structure composition and ecosystem properties through the formation of sites with varying ages yet similar attributes. To investigate the ecological mechanisms structuring fungal community composition and function, we quantify phylogenetic β-diversity and functional gene composition across a glacial chronosequence. Distance between sites across the Upper Great Lakes Region of North America, serving as a proxy for time since deglaciation, enable us to investigate the impact of temporal gradients on the assembly of present-day fungal communities.
Microbial Succession of Community Composition and Functional Characteristics
Ecological succession predicts the directional change in community composition following a disturbance. While plant successional dynamics have been well documented in ecology over the last century, we still do not understand the extent to which soil microbial communities change through time. Changes in plant community composition may drive concurrent shifts in the belowground community as plant species differ in their biochemical composition and litter production and microbes vary in their ability to decompose components of plant litter. Together, the succession of plant communities and their functional characteristics provide a mechanism by which soil microbial communities change through time.
To test this idea, I investigate changes in microbial composition and functional potential across a series of nine established old fields, ranging from 16 to 86 years since agricultural abandonment, at the Cedar Creek Ecosystem Reserve in MN. We quantify microbial composition according to fungal and bacterial species richness and B-diversity. Further, we investigate functional potential using two approaches: shotgun metagenomics to calculate the composition of genes encoding enzymes involved in the decay of plant litter and extracellular enzyme assays. Plant, soil, and root characteristics are collected to understand the primary factors contributing to differences in microbial function during secondary succession.
Role of Assembly History in Structuring Fungal Communities
Community assembly history, or the stochastic sequence and timing of species arrival, may be an important ecological force shaping competitive outcomes and community composition. Species that become established early have a greater chance of competitive dominance than do later arrivals, a concept known as priority effects. Recent evidence suggests that assembly history can structure microbial community composition and function. Other environmental factors, including litter biochemistry, function as strong selective forces on microbial community composition and rates of decomposition. Yet, the relative importance of deterministic factors versus community assembly history in structuring communities remains an unresolved issue in ecology. Using saprotrophic fungi as a model system, I evaluate the relative strength of assembly history versus selection in structuring the composition and function of fungal communities in a microcosm experiment.
Mechanisms of microbial community assembly
Links between microbial composition and function
Interactions between aboveground and belowground communities
Photo Credits: Dave Brenner