Department of Biology

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    The effects of fungal root endophytes on plant growth: a meta-analysis
    (Mycorrhiza (Springer), 2012-07) Mayerhofer, Michael; Kernaghan, Gavin; Harper, Karen A.
    Fungal root endophytes are plant associates that colonize root tissue internally without causing any obvious harm to their host. Although ubiquitous, this relationship is not well understood. Our objectives were to determine the effects of fungal root endophyte inoculation on plant biomass and nitrogen concentration by conducting an extensive meta-analysis. We also explored the effects of experimental conditions on the host–endophyte relationship. We performed analyses weighted with non-parametric variance on plant response to root endophytes from the Ascomycetes (excluding the Clavacipitaceae), including categorical analyses of 21 experimental factors, ranging from the identity of the host and the endophyte, to the composition of the growing medium. The response of total biomass to endophyte inoculation was 18 % lower than non-inoculated controls, while individually, root biomass, shoot biomass, and nitrogen concentration responses to endophyte inoculation were neutral. The identities of both the host and the endophyte had an influence, as did the original source of the endophyte (whether or not the isolate used originated from the same host species). Experimental conditions also influenced the plant–endophyte relationship, with the most important being the availability and sources of carbon and organic nitrogen, particularly peat moss. Although our analysis demonstrates that overall plant biomass and nitrogen concentration responses to ascomycetous root endophyte inoculation is neutral to negative, these results are somewhat confounded by among-study differences in experimental conditions, which undoubtedly contribute to the high levels of variability in plant response seen in the literature.
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    Development and activity of early saproxylic fungal communities in harvested and unmanaged boreal mixedwood stands
    (European Journal of Forest Research (Springer), 2014-09) Kebli, Hedi; Kernaghan, Gavin; Drouin, Pascal; Brais, Suzanne
    Limited scientific information is currently available regarding saproxylic fungal communities in the boreal forest of North America. We aimed to characterize the community development, richness and activity of saproxylic fungi on fresh wood in harvested and unmanaged boreal mixedwood stands of northwestern Québec (Canada). Fresh wood blocks (n = 480) of balsam fir (Abies balsamea (L.) Mill.) and trembling aspen (Populus tremuloides Michx.) were placed on the forest floor in a range of stand conditions (n = 24). Blocks were harvested every 6 months for up to 30 months and characterized for species composition and richness (PCR–DGGE, DNA sequencing), respiration, wood density and lignin and cellulose content. Colonization by a wide range of functional groups proceeded rapidly under different stand conditions. We detected a total of 35 different fungal operational taxonomic units, with the highest species richness at the wood block level being observed within the first 12 months. No differences in community composition were found between wood host species or among stand conditions. However, the variability in fungal communities among blocks (β diversity) was lower on trembling aspen wood compared with balsam fir and decreased over time on trembling aspen wood. Also, fungal activity (respiration and wood decomposition) increased on trembling aspen wood blocks and species richness decreased on balsam fir wood over time in partial-cut sites. The overlap in tree composition among stands, the high volume of logs and the recent management history of these stands may have contributed to the similarity of the saproxylic fungal community among stand types and disturbances.
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    Colonization of green roof plants by mycorrhizal and root endophytic fungi
    (Ecological Engineering (Elsevier), 2014-10) John, Jesse; Lundholm, Jeremy; Kernaghan, Gavin
    Green roof plants must survive hot and dry conditions in low nutrient artificial growing media. Although soil microorganisms such as arbuscular mycorrhizal fungi (AMF) can ameliorate these constraints by increasing water and mineral uptake, virtually nothing is known about the microbes associated with the roots of green roof plants. We determined levels of AMF and dark septate endophyte (DSE) colonization of plants grown for four years on an experimental green roof in Halifax, Nova Scotia. Green roof plant species included the forb Solidago bicolor, the grasses Danthonia spicata and Poa compressa and the succulent Sedum acre. We also assessed root colonization of these same species, as well as three additional succulents (Sedum spurium, Rhodiola rosea and Hylotelephium telephium), collected from their natural habitats. We further assessed the inoculum potential of a commercial green roof substrate before and after the introduction of host plants. Levels of AMF colonization were similar within plant species, regardless of collecting location (roof or field). All plant species were colonized except for the succulent S. acre, which is commonly utilized as a green roof plant. The commercial growing medium contained extremely low levels of viable AMF propagules, but this increased significantly after planting with Solidago. Conversely, all species (from roof, field and bioassay) were well colonized by DSE, which appear to differ from the AMF with respect to their pattern of dispersal onto the green roof. Although the widespread use of non-mycorrhizal succulent species such as S. acre precludes the ecosystem services provided by the AMF symbiosis, the benefits of both succulent tissue and AMF could be obtained simultaneously with careful green roof plant selection.
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    Diversity and host preference of fungi co-inhabiting Cenococcum mycorrhizae
    (Fungal Ecology (Elsevier), 2015-10) Kernaghan, Gavin; Patriquin, Glenn
    Diverse fungal assemblages colonize the fine feeder roots of woody plants, including mycorrhizal fungi, fungal root endophytes and soil saprotrophs. The fungi co-inhabiting Cenococcum geophilum ectomycorrhizae (ECM) of Abies balsamea, Betula papyrifera and Picea glauca were studied at two boreal forest sites in Eastern Canada by direct PCR of ITS rDNA. 50 non-Cenococcum fungal sequence types were detected, including several potentially mycorrhizal species as well as fungal root endophytes. Non-melanized ascomycetes dominated, in contrast to the dark septate endophytes (DSE) reported in most culture dependent studies. The results demonstrate significant differences in root associated fungal assemblages among the host species studied. Fungal diversity was also host dependent, with P. glauca roots supporting a more diverse community than A. balsamea. Differences in root associated fungal communities may well influence ecological interactions among host plant species.
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    The potential for mycorrhizae to improve green roof function
    (Urban Ecosystems (Springer), 2016-07) John, Jesse; Kernaghan, Gavin; Lundholm, Jeremy
    The selection of plant species for use on green roofs has been based primarily on their ability to cope with the harsh climatic conditions of the urban rooftop environment. However, green roof plants must also survive in engineered substrates that often lack organic material and beneficial soil microorganisms such as mycorrhizal fungi. We review the literature on mycorrhizae in the context of green roof ecosystems, identifying aspects of green roof functioning that could be enhanced through the integration of mycorrhizal fungi. Although relatively few studies have addressed the influence of mycorrhizal symbiosis on green roof plants specifically, we include information from a variety of naturally occurring habitats with analogous growing conditions. The available literature suggests that the incorporation of mycorrhizal fungi can improve a number of green roof functional attributes, including plant diversity, drought resilience, leachate quality, nutrient use efficiency and carbon sequestration, all while reducing the need for external nutrient inputs. We present evidence that mycorrhizal fungi are of general benefit to green roof ecosystems, and can be effectively integrated into green roof design. We recommend methods for this integration and propose future research directions.
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    Acid protease production in fungal root endophytes
    (Mycologia (Taylor & Francis), 2017-01) Mayerhofer, Michael; Fraser, Erica; Kernaghan, Gavin
    Fungal endophytes are ubiquitous in healthy root tissue, but little is known about their ecosystem functions, including their ability to utilize organic nutrient sources such as proteins. Root-associated fungi may secrete proteases to access the carbon and mineral nutrients within proteins in the soil or in the cells of their plant host. We compared the protein utilization patterns of multiple isolates of the root endophytes Phialocephala fortinii s.l., Meliniomyces variabilis and Umbelopsis isabellina with those of two ectomycorrhizal (ECM) fungi, Hebeloma incarnatulum and Laccaria bicolor, and the wood-decay fungus Irpex lacteus at pH values of 2–9 on liquid BSA media. We also assessed protease activity using a fluorescently labeled casein assay and gelatin zymography and characterized proteases using specific protease inhibitors. I. lacteus and U. isabellina utilized protein efficiently, while the ECM fungi exhibited poor protein utilization. ECM fungi secreted metallo-proteases and had pH optima above 4, while other fungi produced aspartic proteases with lower pH optima. The ascomycetous root endophytes M. variabilis and P. fortinii exhibited intermediate levels of protein utilization and M. variabilis exhibited a very low pH optimum. Comparing proteolytic profiles between fungal root endophytes and fungi with well defined ecological roles provides insight into the ecology of these cryptic root associates.
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    Fungal endophytes of wild and hybrid Vitis leaves and their potential for vineyard biocontrol
    (Canadian Journal of Microbiology, 2017-04) Kernaghan, Gavin; Mayerhofer, Michael; Griffin, Amanda
    Plants are colonized by diverse assemblages of fungal endophytes that have potential as biocontrol agents for a variety of crops, including grapevine. Although the diversity of symbionts can be very high in wild plants, the fungal endophytes of wild Vitis plants have not yet been investigated. We surveyed the fungal endophytes of 6 wild populations of Vitis riparia, as well as a cold-tolerant, hybrid grapevine in 5 vineyards (1 certified organic), using 454 pyrosequencing. We detected between 43 and 235 operational taxonomic units per sample, with the highest richness and diversity in the wild, the lowest in conventional vineyards, and intermediate levels in the organic vineyard. Wild plants supported a range of taxa not seen in the conventional vineyards, and vineyards were dominated by relatively few taxa. We also isolated fungi from the wild plants and tested them for their ability to inhibit pathogens of grapevine. Several wild isolates (e.g., Ramularia spp.) were strongly inhibitory to grapevine pathogens. We show that wild Vitis supports a distinct and highly diverse community of fungal endophytes and may represent a rich repository of potential vineyard biocontrol agents.
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    Fungal succession during the decomposition of ectomycorrhizal fine roots
    (Microbial Ecology, 2019) Gray, Logan; Kernaghan, Gavin
    Ectomycorrhizal (ECM) fine roots account for a substantial proportion of forest production and their decomposition releases large amounts of nutrients to the soil ecosystem. However, little is known about the fungi involved in ECM decomposition, including assemblages of fungal saprotrophs, endophytes, and the ECM fungi themselves. To follow fungal succession during the degradation of senescing fine roots, understory seedlings of Abies balsamea and Picea rubens at two sites in the Acadian forest of Nova Scotia were either severed at the root collar or left as controls. Root systems were collected sequentially over two growing seasons and assessed for fine root loss and ECM mantle integrity. ECM were identified by ITS-PCR and grouped into broad morphological categories. Fungal communities colonizing the senescing fine roots were also monitored by systematically constructing clone libraries over the course of the experiment. ECM with cottony, weakly pigmented mantles (e.g., Cortinarius) degraded within the first year. Those with cottony, but intensely pigmented mantles (Piloderma), and smooth mantles with weak pigmentation (Russulaceae) degraded more slowly. Smooth, melanized ECM (Cenococcum and Tomentella) generally maintained integrity over the course of the experiment. Rates of fine root loss and changes in ECM mantle integrity were positively correlated with soil temperature. ECM DNA was detected throughout the experiment, and was not replaced by that of saprotrophic species during the two seasons sampled. However, fungal root endophytes (e.g., Helotiaceae) initially increased in abundance and then decreased as mantles degraded, suggesting a possible role in ECM decomposition.
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    Fungal species selection during ectomycorrhizal grazing by Collembola
    (Symbiosis, 2019-05) LeFait, Alexis; Gailey, James; Kernaghan, Gavin
    Collembola are one of the most abundant groups of arthropods, with fungi being an important part of their diet. Collembolan grazing of ectomycorrhizae (ECM) can sever connections between the host root and hyphal networks, interrupting nutrient flow and negatively impacting plant growth. Much of the previous information on interactions between Collembola and ECM has been based on mycelium grown in pure culture, which has artificially high nutrient levels and may lack physical and chemical grazing deterrents seen when ECM form on plant roots. We investigated Collembola feeding preferences by offering naturally occurring ECM, identified by ITS sequencing, to Folsomia candida and Protaphorura armata. We also assessed the gut content fungi of Folsomia collected in a mature Pinus strobus stand. We found that some ECM types, including the Tricholoma aestuans, Piloderma bicolor and the tuburculate ECM of Suillus spraguei, were readily grazed, while Cenococcum geophilum and Lactarius vinaceorufescens were unpalatable. Fungi forming unpalatable ECM were readily grazed when not in symbiosis with the host root.