Suppression of root-endogenous fungi in persistently inundated Typha roots

ABSTRACT

Wetland soils are defined by anoxic and reducing conditions that impose biogeochemically hostile conditions on plant roots and their endogenous fungal communities. The cosmopolitan wetland plant Typha L. mitigates root-zone anoxia efficiently, such that roots of these plants may constitute fungal habitats similar to roots in subaerially exposed soils. Alternatively, fungi may compete with plant cells for limited oxygen in inundated roots. We hypothesized that extrinsic environmental factors may reduce fungal incidence and affect fungal community structure within inundated roots as compared with those in subaerially exposed soils. We sampled roots of Typha spp. plants across inundation gradients in constructed reservoirs; root subsamples were microscopically examined for fungal structures, and morphologically distinct fungal endophytes were cultured and isolated from surface-sterilized subsamples. We found that the incidence of fungal hyphae was suppressed for all types of vegetative mycelia when roots were inundated, regardless of depth, but that there were no obvious differences in community composition of fungi cultured from roots growing in inundated versus subaerially exposed soils. This suggests that the suppression of hyphae we observed in root samples did not result from changes in community composition. Instead, low hyphal incidence in inundated Typha roots may reflect germinal inhibition or unsuccessful initial colonization, possibly owing to plant-mediated redox dynamism in the surrounding soil. No variation was seen in the incidence of asexual spores, or chytridiomycetes, nor were there significant differences between geographically disparate sampling sites. Communities of root-endogenous fungi may therefore be influenced more strongly by external environmental factors than by the environments that plant roots comprise.

KEYWORDS:

• Aquatic macrophytes
• dark septate fungi
• endophytes
• hydric soil
• root-associated fungi
• wetlands

ACKNOWLEDGMENTS

We thank Abby Glauser (University of Minnesota), Taylor Patterson (Syracuse University), Olivia Lynch (University of Kansas), and Jacob Stops (Haskell Indian Nations University) for assistance with laboratory and field work. Comments from Editor Arnold and two anonymous reviewers were much appreciated, having genuinely improved the manuscript.

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Funding

This research was supported in part by the Natural Sciences and Engineering Research Council of Canada (NSERC-CRSNG) grant PGS-D2-438186-2013 to Ashley A Klymiuk, and by the Kansas Biological Survey.