Decomposition of timothy (Phleum pratense L.) litter in a strip-mined soil: nutrient dynamics, fungal colonization, and decomposer potential

Bibliography: p. 179-190

Data from: Topology of tree-mycorrhizal fungus interaction networks in xeric and mesic Douglas-fir forests

1. From the phytocentric perspective, a mycorrhizal network (MN) is formed when the roots of two or more plants are colonized by the same fungal genet. MNs can be modelled as interaction networks with plants as nodes and fungal genets as links. The potential effects of MNs on facilitation or competition between plants are increasingly recognized, but their network topologies remain largely unknown. This information is needed to understand the ecological significance of MN functional traits. 2. The objectives of this study were to describe the interaction network topologies of MNs formed between two ectomycorrhizal fungal species, Rhizopogon vesiculosus and R. vinicolor, and interior Douglas-fir trees at the forest stand scale, identify factors leading to this structure and to contrast MN structures between forest plots with xeric versus mesic soil moisture regimes. 3. Tuberculate mycorrhizas were sampled in six 10 × 10 m plots with either xeric or mesic soil moisture regimes. Microsatellite DNA markers were used to identify tree and fungal genotypes isolated from mycorrhizas and for comparison with reference tree boles above-ground. 4. In all six plots, trees and fungal genets were highly interconnected. Size asymmetries between different tree cohorts led to non-random MN topologies, while differences in size and connectivity between Rhizopogon species-specific subnetwork components contributed towards MN nestedness. Large mature trees acted as network hubs with a significantly higher node degree compared to smaller trees. MNs representing trees linked by R. vinicolor genets were mostly nested within larger, more highly connected R. vesiculosus-linked MNs. 5. Attributes of network nodes showed that hub trees were more important to MN topology on xeric than mesic sites, but the emergent structures of MNs were similar in the two soil moisture regimes. 6. Synthesis. This study suggests MNs formed between interior Douglas-fir trees and R. vesiculosus and R. vinicolor genets are resilient to the random loss of participants, and to soil water stress, but may be susceptible to the loss of large trees or fungal genets. Our results regarding the topology of MNs contribute to the understanding of forest stand dynamics and the resilience of forests to stress or disturbance

Ectomycorrhizal fungal communities in young forest stands regenerating after clearcut logging

The effects on the ectomycorrhizal fungal community of clearcut logging, which is used to harvest millions of hectares of ectomycorrhizal forest annually, has been studied for a number of years. Here, we review current knowledge of inoculum sources for ectomycorrhizal fungi in forests and then re-examine earlier studies of ectomycorrhizas on young trees in regenerating stands. We conclude that, taken separately from the effects of site preparation, the major impact of clearcut logging is to change the species composition of the ectomycorrhizal fungal community rather than to reduce the percentage of roots colonized. A thorough examination of site preparation treatments suggests that the changes in fungal species composition are driven by changes in the biology and chemistry of the soil environment after clearcutting as much as they are by loss or change in fungal inoculum. This is an important conclusion because it implies that these new ectomycorrhizal fungal communities are better adapted to the new conditions than the ones in the forest would have been. The shift in fungal species composition and diversity will have implications for seedling establishment and competition. The effects of individual fungi or diverse assemblages of fungi on seedling growth, and effects of changes in the ability of young trees to associate with a common mycelium are discussed

Data from: Vertical partitioning between sister species of Rhizopogon fungi on mesic and xeric sites in an interior Douglas-fir forest

Understanding ectomycorrhizal fungal (EMF) community structure is limited by a lack of taxonomic resolution and autecological information. Rhizopogon vesiculosus and R. vinicolor (Basidiomycota) are morphologically and genetically related species. They are dominant members of interior Douglas-fir (Pseudotsuga menziesii var. glauca) EMF communities, but mechanisms leading to their coexistence are unknown. We investigated the microsite associations and foraging strategy of individual R. vesiculosus and R. vinicolor genets. Mycelia spatial patterns, pervasiveness and root colonization patterns of fungal genets were compared between Rhizopogon species and between xeric and mesic soil moisture regimes. Rhizopogon spp. mycelia were systematically excavated from the soil and identified using microsatellite DNA markers. Rhizopogon vesiculosus mycelia occurred at greater depth, were more spatially pervasive, and colonized more tree roots than R. vinicolor mycelia. Both species were frequently encountered in organic layers and between the interface of organic and mineral horizons. They were particularly abundant within microsites associated with soil moisture retention. The occurrence of R. vesiculosus shifted in the presence of R. vinicolor towards mineral soil horizons, where R. vinicolor was mostly absent. This suggests that competition and foraging strategy may contribute towards the vertical partitioning observed between these species. R. vesiculosus and R. vinicolor mycelia systems occurred at greater mean depths and were more pervasive in mesic plots compared to xeric plots. The spatial continuity and number of trees colonized by genets of each species did not significantly differ between soil moisture regimes

Competition between saccharomyces cerevisiae and saccharomyces uvarum in controlled chardonnay wine fermentations

Saccharomyces cerevisiae is usually the dominant yeast in winemaking. However, other yeast species such as Saccharomyces uvarum are also able to conduct and complete alcoholic fermentation. S. uvarum is a cryotolerant yeast that has been found dominating low-temperature fermentations at commercial wineries around the world, but little research has been conducted to investigate its competitive abilities relative to commercial S. cerevisiae strains. Here, controlled Chardonnay fermentations were conducted with a commercial S. cerevisiae strain and an indigenous S. uvarum strain inoculated at different initial ratios and two different temperatures. Both strains fermented well at 24°C, and both strains fermented slowly at 15°C. S. cerevisiae was more competitive than S. uvarum when inoculated at an equal or greater ratio. However, S. uvarum was better able to grow and compete with S. cerevisiae at a lower fermentation temperature and, when inoculated at an equal ratio, was able to maintain a 25% relative abundance throughout fermentation, contributing to the volatile-compound profile of the wine. Volatile-compound production was distinct for the two yeast strains, with S. uvarum producing generally higher amounts of volatile compounds, especially at the lower fermentation temperature, including higher amounts of 2-phenylethyl acetate (honey/spice/ floral) and ethyl 2-methyl butanoate (apple/strawberry). When both strains co-existed in fermentation, the resulting volatile profile was unique in that it differed from either single-strain fermentation. This study is the first to test coinoculation of S. cerevisiae and S. uvarum at different ratios and different fermentation temperatures and highlights the potential for the use of indigenous S. uvarum strains in isolation or in combination with S. cerevisiae to produce unique, quality wines.</p

Beiler,etal_Datapack_JEcol-2014-0405.R2

Sample location and genetic data from: Topology of tree-mycorrhizal fungus interaction networks in xeric and mesic Douglas-fir forest

The Interaction of Two Saccharomyces cerevisiae Strains Affects Fermentation-Derived Compounds in Wine

Previous winery-based studies showed the strains Lalvin® RC212 (RC212) and Lalvin® ICV-D254 (D254), when present together during fermentation, contributed to >80% relative abundance of the Saccharomyces cerevisiae population in inoculated and spontaneous fermentations. In these studies, D254 appeared to out-compete RC212, even when RC212 was used as the inoculant. In the present study, under controlled conditions, we tested the hypotheses that D254 would out-compete RC212 during fermentation and have a greater impact on key fermentation-derived chemicals. The experiment consisted of four fermentation treatments, each conducted in triplicate: a pure culture control of RC212; a pure culture control of D254; a 1:1 co-inoculation ratio of RC212:D254; and a 4:1 co-inoculation ratio of RC212:D254. Strain abundance was monitored at four stages. Inoculation ratios remained the same throughout fermentation, indicating an absence of competitive exclusion by either strain. The chemical profile of the 1:1 treatment closely resembled pure D254 fermentations, suggesting D254, under laboratory conditions, had a greater influence on the selected sensory compounds than did RC212. Nevertheless, the chemical profile of the 4:1 treatment, in which RC212 dominated, resembled that of pure RC212 fermentations. Our results support the idea that co-inoculation of strains creates a new chemical profile not seen in the pure cultures. These findings may have implications for winemakers looking to control wine aroma and flavor profiles through strain selection.Arts and Sciences, Irving K. Barber School of (Okanagan)Non UBCBiology, Department of (Okanagan)ReviewedFacult

Glycosidically-Bound Volatile Phenols Linked to Smoke Taint: Stability during Fermentation with Different Yeasts and in Finished Wine

When wine grapes are exposed to smoke, there is a risk that the resulting wines may possess smoky, ashy, or burnt aromas, a wine flaw known as smoke taint. Smoke taint occurs when the volatile phenols (VPs) largely responsible for the aroma of smoke are transformed in grape into a range of glycosides that are imperceptible by smell. The majority of VP-glycosides described to date are disaccharides possessing a reducing β-d-glucopyranosyl moiety. Here, a two-part experiment was performed to (1) assess the stability of 11 synthesized VP-glycosides towards general acid-catalyzed hydrolysis during aging, and (2) to examine whether yeast strains differed in their capacity to produce free VPs both from these model glycosides as well as from grapes that had been deliberately exposed to smoke. When fortified into both model and real wine matrices at 200 ng/g, all VP-disaccharides were stable over 12 weeks, while (42–50 ng/g) increases in free 4-ethylphenol and p-cresol were detected when these were added to wine as their monoglucosides. Guaiacol and phenol were the most abundantly produced VPs during fermentation, whether originating from natural VP-precursors in smoked-exposed Pinot Noir must, or due to fortification with synthetic VP-glycosides. Significant yeast strain-specific differences in glycolytic activities were observed for phenyl-β-d-glycopyranoside, with two strains (RC212 and BM45) being unable to hydrolyze this model VP, albeit both were active on the guaiacyl analogue. Thus, differences in Saccharomyces cerevisiae β-glucosidase activity appear to be influenced by the VP moiety.Science, Irving K. Barber Faculty of (Okanagan)Biology, Department of (Okanagan)Chemistry, Department of (Okanagan)ReviewedFacult

An indigenous Saccharomyces uvarum population with high genetic diversity dominates uninoculated Chardonnay fermentations at a Canadian winery.

Saccharomyces cerevisiae is the primary yeast species responsible for most fermentations in winemaking. However, other yeasts, including Saccharomyces uvarum, have occasionally been found conducting commercial fermentations around the world. S. uvarum is typically associated with white wine fermentations in cool-climate wine regions, and has been identified as the dominant yeast in fermentations from France, Hungary, northern Italy, and, recently, Canada. However, little is known about how the origin and genetic diversity of the Canadian S. uvarum population relates to strains from other parts of the world. In this study, a highly diverse S. uvarum population was found dominating uninoculated commercial fermentations of Chardonnay grapes sourced from two different vineyards. Most of the strains identified were found to be genetically distinct from S. uvarum strains isolated globally. Of the 106 strains of S. uvarum identified in this study, four played a dominant role in the fermentations, with some strains predominating in the fermentations from one vineyard over the other. Furthermore, two of these dominant strains were previously identified as dominant strains in uninoculated Chardonnay fermentations at the same winery two years earlier, suggesting the presence of a winery-resident population of indigenous S. uvarum. This research provides valuable insight into the diversity and persistence of non-commercial S. uvarum strains in North America, and a stepping stone for future work into the enological potential of an alternative Saccharomyces yeast species