Does fungal competitive ability explain host specificity or rarity in ectomycorrhizal symbioses?

Abstract

Two common ecological assumptions are that host generalist and rare species are poorer competitors relative to host specialist and more abundant counterparts. While these assumptions have received considerable study in both plant and animals, how they apply to ectomycorrhizal fungi remains largely unknown. To investigate how interspecific competition may influence the anomalous host associations of the rare ectomycorrhizal generalist fungus, Suillus subaureus, we conducted a seedling bioassay. Pinus strobus seedlings were inoculated in single-or two-species treatments of three Suillus species: S. subaureus, S. americanus, and S. spraguei. After 4 and 8 months of growth, seedlings were harvested and scored for mycorrhizal colonization as well as dry biomass. At both time points, we found a clear competitive hierarchy among the three ectomycorrhizal fungal species: S. americanus > S. subaureus > S. spraguei, with the competitive inferior, S. spraguei, having significantly delayed colonization relative to S. americanus and S. subaureus. In the singlespecies treatments, we found no significant differences in the dry biomasses of P. strobus seedlings colonized by each Suillus species, suggesting none was a more effective plant symbiont. Taken together, these results indicate that the rarity and anomalous host associations exhibited by S. subaureus in natural settings are not driven by inherently poor competitive ability or host growth promotion, but that the timing of colonization is a key factor determining the outcome of ectomycorrhizal fungal competitive interactions.

Formations of mycorrhizal symbiosis alter the phenolic heteropolymers in roots and leaves of four temperate woody species

“…Molecular identification of EcM fungi in the colonized roots of inoculated seedlings was done by extracting DNA using the REDExtract‐N‐Amp protocol (Sigma‐Aldrich, St Louis, MO, USA). The PCR using the fungal‐specific primer pair ITS1F‐ITS4 was conducted using the thermocycling conditions (Kennedy et al ., 2020). The PCR products were cleaned with Exo‐SAP IT (USB Corp., Cleveland, OH, USA) and sequenced in forward direction with the ITS1F primer at the UMN Genomics Center.…”

Suillus: an emerging model for the study of ectomycorrhizal ecology and evolution

“…Working with a set of species that are commonly associated with Pinus strobus , Kennedy et al . (2020) found a clear competitive hierarchy of S. americanus > S. subaureus > S. spraguei . The outcome of the competitive interactions appeared to be largely the result of differences in spore germination timing, with S. americanus being the first and most consistent to colonize P. strobus seedling root tips, followed by S. subaureus , and then S. spraguei .…”

“…Both amateur and professional mycologists alike have long targeted the collection of charismatic Suillus mushrooms, with over 46 000 vouchered specimens currently digitized in the MyCoPortal collections database (https://www.mycoportal.org/) and over 62 000 observations of Suillus currently in iNaturalist (https://www.inaturalist.org/). Vouchered collections have facilitated phylogenetic reclassifications across the genus (Nguyen et al ., 2016b), illuminated the association between species diversification and host shifts (Zhang et al ., 2022), clarified species rarity (Kennedy et al ., 2020), and helped to identify the biotic and abiotic factors facilitating range shifts and invasion potential (Pietras et al ., 2018). The collection of Suillus fruit bodies is the first step to obtaining pure cultures, spores for use in bioassays, and preserved specimens for morphological studies or new species descriptions.…”

Common and lifestyle‐specific traits of mycorrhizal root metabolome reflect ecological strategies of plant–mycorrhizal interactions

“…Molecular identification of EM fungal identities was done by extracting DNA using the REDEextract-N-Amp protocol (Sigma-Aldrich). PCR using the fungal-specific primer pair ITS1F-ITS4 was conducted using the thermocycling conditions (Kennedy et al, 2020). PCR products were cleaned with Exo-SAP IT (USB Corp.) and sequenced in forward direction with the ITS1F primer at the UMN Genomics Center.…”