Fungi are a highly diverse kingdom of organisms, ranging from microscopic yeasts to the world’s largest living organism, the honey fungus, whose fruiting bodies can span across nearly 4 km of land (Fleming, N. 2014). At first glance, many fungi seem to bear a significant resemblance to members of the plant kingdom, while in actual fact they are far more closely related to animals!
Fungi are heterotrophic organisms that obtain their nutrients by growing on, or amongst, their food source. As such, fungi serve important ecological roles, as primary decomposers, or as mutualistic symbionts with plants. The former, the saprophytic fungi, serve as recyclers of nutrients by processing decayed matter. The latter, the mycorrhizal fungi, occur in symbiosis with the vast majority of vascular plants and are instrumental in a plant’s ability to capture water and essential nutrients (Evert, R. F., and S. E. Eichhorn. 2013).
The goal of this project is to shed some light on these unique organisms. This will be done by examining the relationship between the species richness of saprophytic ascomycetes and their environment.
Fungal fruiting bodies are observable throughout the spring and summer months, but reach their peak abundance and diversity in autumn (Kricher, J.C., and Morrison, G. 1998). This can be attributable to the yearly re-introduction of additional nutrients for litter layer saprobes of the forest floor, caused by the shedding of dead leaves from treetops overhead.
Of the major groups of fungi, Ascomycota is the most expansive, comprising of over 32,300 taxonomically classified mushroom species (Evert, R. F., and S. E. Eichhorn. 2013). Further subdivided, the Ascomycota are represented by Saccharomycotina, or yeasts, the plant parasites of the Taphrinomycotina, and the macroscopically recognizable Pezizomycotina.
Pezizomycotina can form epigeous ascocarps, above ground fruiting bodies, or reproductive organs, that serve as a means of spore dispersal. Ascocarps differ from their counterparts, basidiocarps, in that they form their spores internally and are generally forcibly expelled, as opposed to the external formation of spores on the cap underside in structures such as gills, characteristic of Basidiomycota.
Saprophytic fungi and bacteria access their leafy nutrition following an initial breach by litter animals and insects, whose chewing creates minute access points in bites and incisions. However, not all nutrient sources are equally distributed, nor are they as readily available. Leaves vary in their ease of decomposition, depending on factors such their cellulose and lignin content; the strength of the waxy cuticle, their protective layer; the amount of tannins or phenolics, their defense compounds (Kricher, J.C., and Morrison, G. 1998).
Leaf decomposition rates can be inferred by the availability of their nutrients, expressed by their carbon to nitrogen composition ratio (C:N). Carbon containing molecules, like cellulose and lignin, are more difficult metabolites to break down compared to nitrogen containing molecules, like proteins. Therefore, a lower C:N ratio suggests materials that can be more readily broken down by decomposers. Sugar maples, for instance, have relatively low C:N ratio (20:1); beech (49:1); high ratios can be found in pine (66:1); and tamarack (113:1) (Kricher, J.C., and Morrison, G. 1998). C:N ratio has been found to be the most important factor affecting microbes in the soil according to Gyllenberg H. (1954).
Most ascomycetes are soft rot species, meaning they can break down the cellulose and hemi-cellulose in plants, but not tougher substances like lignin (Mäkelä, M. R., et al., 2015). This could render deciduous trees more susceptible to ascomycete colonization, as they generally have a higher cellulose and hemicellulose content compared to that of lignin. Coniferous species, on the other hand, contain more lignin and resins (Macdonald J., et al., 2016; McKnight, T.E. & Mullins, E. J., 1981).
Leaf litters from different tree species have been shown to encourage distinction in microbial communities during decomposition, resulting from the makeup of the litter itself and the hitherto underlying microbial community, and tree species can account for almost half of the variability in fungal litter community composition (Prescott, C. E., and Grayston, S. J. 2013).
The experimental site of the study was the Morgan Arboretum in St-Anne-de-Bellevue on the western tip of the island of Montreal. Acquired by McGill in 1945, reforestation of pastures ensued, with the intention of grouping collections of trees, native and exotic, suited for specific in situ soil types and capable of adapting to the climate. Many of these tree stands are considered to have reached a respectable age (Godbout, A. 1998).
Our study aims to look the interactions between dominant forest type and the species richness of Ascomycota found in these forests. This is to be done by sampling deciduous and coniferous forest stands and determining through statistical analysis if there is a significant difference in the number of ascomycetes in each forest type. We hypothesize that there will be a lesser amount of ascomycete richness in the coniferous forest in autumn based on the availability of nutrients.
To gather data for this study, 12 five by five meter plots were made in the Morgan Arboretum, half in deciduous dominant forest types and half in coniferous dominant forest types. Different tree stands were chosen at the start of each lab, consisting of one coniferous and one deciduous dominated section in close proximity, where 2 plots in each were to be performed. On October 13th, the beech forest stand was visited for the deciduous plots and the mixed red, white, black and Norway spruce section was visited to perform the coniferous plots. On October 20th, plots were performed in the Sugar Maple as well as the mixed tamarack and Norway spruce tree stands. On October 27th, the mixed sugar maple and beech and the red pine and Norway spruce tree stands were used. The locations of the experimental plots within tree stands were selected at random. The end of a thrown stick was used a compass point, directing the researchers path until areas with significant amounts of deadfall were found. The plots were measured using a 5 meter piece of flagging tape and delineated with small flags.
See our video on our sampling techniques.
The species richness of mushrooms within plots was ascertained by counting and identifying the different fruiting bodies of ascomycete species found within the plot. Each fungus was described including the location they grew, their smell, texture and shape, as well as photographed with an object as reference point. Fungi that were not identifiable on site were taken as samples in separate brown paper bags for later identification.
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Macdonald J, Goacher RE, Abou-Zaid M, & Master ER. (2016). Comparative analysis of lignin peroxidase and manganese peroxidase activity on coniferous and deciduous wood using ToF-SIMS. Applied Microbiology and Biotechnology, 100, 8013-20. doi: 10.1007/s00253-016-7560-2
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