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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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    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.