Interactions Among Fungal Guilds
With the rise of high-throughput sequencing, the ability to analyze the interactions among different fungal guilds has been greatly enhanced. Through a collaborative effort, we built the bioinformatic tool, FUNGuild, to parse high-throughput fungal datasets by ecological guild. This work has allowed us to explore interactions among different fungal guilds in a diverse range of study systems. For example, we teamed up with Jonathan Schilling to examine the microbial 'handoffs' between endophytic fungi and wood decay fungi in decomposing boreal forest birch logs. Lauren Cline led the data generation and writing push for that project - see a pic of the field work here. Parallel work on this 'handoff' in a lab setting was also done in collaboration with Jonathan and Zewei Song. More recently, we have focused on the interactions between ectomycorrhizal fungi and saprotrophic fungi during the decomposition of forest leaf litter. This work, widely known as the 'Gadgil Effect', has been spearheaded by Chris Fernandez, who's multi-year field studies at the Cedar Creek Ecosystem Science Reserve demonstrated that the effect of ectomycorrhizal fungi on leaf litter decomposition strongly depends of both fungal community composition and substrate chemistry.
Fungal Necromass Decomposition
Along with their well-documented effects on host tree productivity, mycorrhizal fungi also play an important role in soil carbon and nutrient cycling through the input and decomposition of their own hyphae. This fungal 'necromass' is a dynamic and fast-cycling resource pool that affects both soil carbon storage and nitrogen availability. Over the past 4 years, we have focused on characterizing how a range of ecological factors, both intrinsic (melanin content and mycelial morphology) and extrinsic (vegetation type and climate warming), drive rates of fungal necromass decomposition. We have also sequenced the microbial communities on decaying necromass in many experimental settings to better understand the associated shifts in microbial community structure over time. This work has involved many collaborations, both nationally (Kate Heckman, Katie Schreiner, Jennifer Pett-Ridge) and internationally (Havard Kauserud, Line Nybakken, Marc Buee). Most recently, in collaboration with Sarah Hobbie, we have deployed multiple types of necromass in plots receiving experimental carbon or nitrogen addition at the Cedar Creek Ecosystem Science Reserve to assess the long-term dynamics of fungal necromass decomposition.
Ectomycorrhizal Host Specificity
Relative to other groups of mycorrhizal fungi, ectomycorrhizal fungi have a greater number of species that only associate with particular types of plant hosts. After many years studying the ecological factors controlling the high specificity of Alnus-associated (Alder) mycorrhizal communities, we have focused in Minnesota on a diverse and cosmopolitan group of mushrooms in the genus Suillus. Members of this genus are known to associate specifically with three host tree genera in the family Pinaceae (Larix, Pseudotsuga, and Pinus), but our work has found that some Suillus species are able to form 'anomalous' associations with other tree hosts. For example, in her thesis research, Lotus Lofgren was able to show that Suillus subaureus could form ectomycorrhizas with Quercus seedlings, but only when Pinus seedlings were also present. We often study patterns of host specificity using both field-based root tip sequencing surveys and experimental laboratory bioassays. Having generated a large number of genomes of different Suillus species with support from NSF and DOE, we have also begun exploring the genomic underpinnings of host specificity. Work on this topic was largely pioneered in the lab by Nhu Nguyen, who is still an active collaborator and the official expert on the taxonomy of this fascinating genus.
Ectomycorrhizal Competitive Dynamics
Significant progress has been made in recent years understanding the influence of interspecific interactions on the structure of ectomycorrhizal fungal communities (click here for an early review from the lab on the topic). We maintain an active interest in studying ectomycorrhizal competition - see lab publications on vertical niche partitioning among ectomycorrhizal fungi (suggesting competition is important) and co-occurrence patterns in Alnus forests (suggesting competition is largely absent). In Minnesota, we teamed up with both Sara Hortal and Ian Anderson at the Australian Hawkesbury Institute for the Environment and Laura Bogar and Kabir Peay at Stanford University to study the interactions among Suillus species that colonize the host genus Larix. That experiment used a split-root approach to test the extent of partner discrimination in ectomycorrhizal symbioses. Our most recent work on this topic has analyzed how fungal competitive ability contributed to the anomalous host associations of Suillus subaureus, which was the focus of an undergraduate honor's thesis by Joe Gagne.