Do fungal communities on prairie plant seeds vary with host identity, fragment size, or both?
Fragmentation may influence plant-soil feedbacks by 1) altering abiotic conditions that in turn influence pathogen pressure, or 2) by limiting dispersal of hosts and/or fungi, therefore affecting pathogen transmission. Characterizing seed-borne fungal diversity at a landscape scale provides a first step toward assessing these mechanisms. We examined seedborne fungal diversity in an experimentally fragmented landscape in Lawrence, Kansas. We buried seeds of three prairie plant species -- Andropogon gerardii, Chamaecrista fasciculata, and Rudbeckia hirta in patches of successional forest in July 2012 and unearthed the seeds prior to emergence in June 2013. Buried seeds were placed in three locations in the experimentally fragmented landscape: (1) small patches, (2) edges of large patches, and (3) centers of large patches. Seeds served as ‘bait’ for potential fungal pathogens. Fungi were cultured from surface-sterilized seeds and identified using ribosomal DNA sequencing. We predicted that fungal diversity would mirror plant diversity, such that large patches with higher plant species richness will harbor more fungal species. If feedbacks play a role in maintaining diversity in our landscape, we also expect to see unique fungal communities associated with each plant species.
Culturing and sequencing has revealed at least 30 unique fungal phylotypes collected from 211 isolates. Four of the five most common phylotypes are taxa assigned to the genus Fusarium based on NCBI BLAST search results. Fusarium is a diverse genus containing multiple plant pathogens, along with saprophytes and endophytes. Other common genera included Bionectria, Alternaria, and Penicillium. Fungal diversity varied according to where in the landscape seeds were buried. Based on rarefaction, fungal diversity was significantly higher across all small patches than in the centers of large patches, such that 95% confidence intervals for rarefaction curves of large patches did not include the accumulation curve of small patches. Using non-metric multidimensional scaling, we found that both host identity and patch size influenced fungal community composition, with distinct fungal communities among large patch centers and small patches, and in the seeds of A. gerardii and R. hirta. This preliminary evidence characterizing landscape-level patterns of fungal community composition provides a foundation for future assessment of mechanisms through which fragmentation influences plant-soil feedbacks, and ultimately, plant species diversity.