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1. Arbuscular Mycorrhizal Tree Communities Have Greater Soil Fungal Diversity and Relative Abundances of Saprotrophs and Pathogens than Ectomycorrhizal Tree Communities

   https://doi.org/10.1128/AEM.01782-21  

   Eagar, Andrew C.; Mushinski, Ryan M.; Horning, Amber L.; Smemo, Kurt A.; Phillips, Richard P.; Blackwood, Christopher B. (January 2022, Applied and Environmental Microbiology)

   Druzhinina, Irina S. (Ed.)

   ABSTRACT Trees associating with different mycorrhizas often differ in their effects on litter decomposition, nutrient cycling, soil organic matter (SOM) dynamics, and plant-soil interactions. For example, due to differences between arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) tree leaf and root traits, ECM-associated soil has lower rates of C and N cycling and lower N availability than AM-associated soil. These observations suggest that many groups of nonmycorrhizal fungi should be affected by the mycorrhizal associations of dominant trees through controls on nutrient availability. To test this overarching hypothesis, we explored the influence of predominant forest mycorrhizal type and mineral N availability on soil fungal communities using next-generation amplicon sequencing. Soils from four temperate hardwood forests in southern Indiana, United States, were studied; three forests formed a natural gradient of mycorrhizal dominance (100% AM tree basal area to 100% ECM basal area), while the fourth forest contained a factorial experiment testing long-term N addition in both dominant mycorrhizal types. We found that overall fungal diversity, as well as the diversity and relative abundance of plant pathogenic and saprotrophic fungi, increased with greater AM tree dominance. Additionally, tree community mycorrhizal associations explained more variation in fungal community composition than abiotic variables, including soil depth, SOM content, nitrification rate, and mineral N availability. Our findings suggest that tree mycorrhizal associations may be good predictors of the diversity, composition, and functional potential of soil fungal communities in temperate hardwood forests. These observations help explain differing biogeochemistry and community dynamics found in forest stands dominated by differing mycorrhizal types. IMPORTANCE Our work explores how differing mycorrhizal associations of temperate hardwood trees (i.e., arbuscular [AM] versus ectomycorrhizal [ECM] associations) affect soil fungal communities by altering the diversity and relative abundance of saprotrophic and plant-pathogenic fungi along natural gradients of mycorrhizal dominance. Because temperate hardwood forests are predicted to become more AM dominant with climate change, studies examining soil communities along mycorrhizal gradients are necessary to understand how these global changes may alter future soil fungal communities and their functional potential. Ours, along with other recent studies, identify possible global trends in the frequency of specific fungal functional groups responsible for nutrient cycling and plant-soil interactions as they relate to mycorrhizal associations. 

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2. Mineral-Associated Organic Matter Concentration Beneath Northern Temperate Trees Varies by Mycorrhizal Type and Leaf Habit

   https://doi.org/10.1007/s10021-024-00949-2  

   Lang, Ashley K; Fitch, Amelia A; Jevon, Fiona V; Hatala_Matthes, Jaclyn; Ayres, Matthew P; Hicks_Pries, Caitlin E (February 2025, Ecosystems)

   Mycorrhizal fungi are important drivers of soil organic matter dynamics, but it can be difficult to isolate the effects of the fungi themselves from co-varying traits of their host trees. For example, many trees with an evergreen leaf habit associate with ectomycorrhizal (ECM) fungi, while many deciduous tree species associate with arbuscular mycorrhizal (AM) fungi. Because leaf habit influences the quantity and quality of organic matter inputs to soil, it is often an important factor in soil carbon and nitrogen dynamics, and thus can mask the effects of mycorrhizal fungi on soil organic matter processes. We evaluated how tree mycorrhizal associations and leaf habit separately influence the amount and composition of mineral-associated organic matter (MAOM) and particulate organic matter (POM) in forest soils in New Hampshire and Vermont, USA. We measured carbon (C) and nitrogen (N) concentrations and C:N ratios of three soil density fractions beneath six tree species that vary in mycorrhizal association and leaf habit. We found lower concentrations of MAOM C and N beneath evergreen vs. deciduous trees, but only for tree species associating with AM fungi. Further, MAOM C:N was higher beneath evergreen trees and beneath trees with ECM fungi rather than AM fungi. These results add to the growing body of support for mycorrhizal fungi as mediators of soil organic matter dynamics, suggesting that the MAOM fraction is more sensitive to leaf habit beneath AM-associated versus ECM-associated trees. Because MAOM decomposition is thought to be less responsive than POM decomposition to changes in soil temperature and moisture, differences in the tendency of AM- and ECM-dominated forests to support MAOM formation and persistence may lead to systematic differences in the response of these forest types to ongoing climate change. 

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3. Higher Soil Respiration Rate Beneath Arbuscular Mycorrhizal Trees in a Northern Hardwood Forest is Driven by Associated Soil Properties

   https://doi.org/10.1007/s10021-019-00466-7  

   Lang, Ashley K.; Jevon, Fiona V.; Ayres, Matthew P.; Hatala Matthes, Jaclyn (December 2019, Ecosystems)

   Soil respiration is the dominant pathway by which terrestrial carbon enters the atmosphere. Many abiotic and biotic processes can influence soil respiration, including soil microbial community composition. Mycorrhizal fungi are a particularly important microbial group because they are known to influence soil chemistry and nutrient cycling, and, because the type of mycorrhizal fungi in an ecosystem can be assessed based on the plant species present, they may be easier than other soil microbes to incorporate into ecosystem models. We tested how the type of mycorrhizal fungi—arbuscular (AM) or ectomycorrhizal (ECM) fungi—associated with the dominant tree species in a mixed hardwood forest was related to soil respiration rate. We measured soil respiration, root biomass, and surface area, and soil chemical and physical characteristics during the growing season in plots dominated by ECM-associated trees, AM-associated trees, and mixtures with both. We found rates of soil respiration that were 29% and 32% higher in AM plots than in ECM and mixed plots, respectively. These differences are likely explained by the slightly higher nitrogen concentrations and deeper organic horizons in soil within AM plots compared with soil in ECM and mixed plots. Our results highlight the importance of considering mycorrhizal associations of dominant vegetation as predictors of carbon cycling processes. Key words: Soil respiration; Mycorrhizal fungi; Carbon; Microbial activity; CO2; Northern hardwood forest. 

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4. SOM density fractions beneath trees of different mycorrhizal types in New England forests

   https://doi.org/10.6073/pasta/a3dcb9cf6ae9e1d29daea46c2c122123  

   Lang, Ashley K; Jevon, Fiona V; Fitch, Amelia A; Hatala Matthes, Jaclyn; Ayres, Matthew P; Hicks Pries, Caitlin E (January 2021, Environmental Data Initiative)

   Recent work suggests mycorrhizal fungi are important drivers of soil organic matter dynamics; however, whether this is a result of the fungi themselves or related traits of their host trees remains unclear. We evaluated how tree mycorrhizal associations and foliar chemistry influence mineral-associated organic matter (MAOM) and particulate organic matter (POM) in temperate forests of northern New England, USA. We measured carbon (C) and nitrogen (N) concentrations and C:N of three soil density fractions beneath six tree species that vary in both mycorrhizal association and foliar chemistry. We found a significant decline in the concentration of MAOM C and N with increasing foliar C:N in soil beneath tree species with arbuscular mycorrhizal (AM), but not ectomycorrhizal (ECM) fungi. The C:N of POM and MAOM was positively associated with the foliar C:N of the dominant tree species in a forest, and MAOM C:N was also higher beneath ECM- rather than AM-associated tree species. These results add to the growing body of support for mycorrhizal fungi as predictors of soil C and N dynamics, and suggest that C concentration in the MAOM fraction is more sensitive to organic matter chemistry beneath AM-associated tree species. Because MAOM decomposition is thought to be less responsive than POM decomposition to changes in soil temperature and moisture, differences in the tendency of AM- vs. ECM-dominated forests to support MAOM formation and persistence may lead to systematic differences in the response of these forest types to ongoing climate change. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

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5. Post-fire Quercus mycorrhizal associations are dominated by Russulaceae, Thelephoraceae, and Laccaria in the southern Appalachian Mountains

   https://doi.org/10.1007/s11557-025-02037-8  

   Hughes, Karen W; Franklin, Jennifer A; Schweitzer, Jennifer; Kivlin, Stephanie N; Case, Alexis; Aldrovandi, Matthew; Matheny, P Brandon; Miller, Andrew N (December 2025, Mycological Progress)

   Abstract Following disturbances such as wildfires, oak seedlings must form a symbiotic association with mycorrhizal fungi to survive. Wildfires, however, reduce available mycorrhizal fungal propagules in the soil. Ectomycorrhizal (ECM) fungi on oak seedlings sampled in severely burned (7 sites), moderately burned (7 sites), and unburned areas (8 sites) in the Great Smoky Mountains National Park were evaluated 21 months after the 2016 Chimney Tops 2 Wildfire by Sanger sequencing of the nuclear ribosomal DNA internal transcribed spacer region (nrITS; fungal barcode). Sequences were aligned and grouped into Operational Taxonomic Units (OTUs) based on well-supported phylogenetic clades and 98–100% nrITS sequence homology with sequences in GenBank. One hundred seventy-nine root-associated fungi comprising 124 OTUs were recovered after removing duplicates (the same fungus on two or more roots of the same plant). The ECM genusRussulawas the most diverse genus (25 OTUs), followed by theThelephora/Tomentellaclade (18 OTUs),Lactifluus(8 OTUs),Lactarius(4 OTUs), and Laccariaaff.laccata(2 OTUs).RussulaOTUs were identified more frequently on oak roots from burned areas and in burned soils, suggesting that someRussulataxa may have a selective advantage in burned areas. High alpha diversity occurred within each of the burn categories, but little overlap of taxa occurred between burn categories (high beta diversity). Approximately half of the recovered OTUs (100/179 total root-associated fungi = 55.9%) were found on a single plant. Oak seedlings growing in moderately and severely burned areas 21 months after a fire were capable of forming root associations with available fungi. In contrast to the expectation that root-associated fungal diversity would be reduced after a wildfire, diversity 1 year after the Chimney Tops 2 Fire was high with ectomycorrhizalLaccaria,Russulaceae, andThelephoraceaedominating. This study suggests that the availability of ECM fungi post-fire is not a barrier to oak re-establishment. 

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