New wrinkles in an old paradigm: neighborhood effects can modify the structure and specificity ofAlnus-associated ectomycorrhizal fungal communities

Abstract

Host identity has been recognized as a key determinant of the structure of ectomycorrhizal (ECM) fungal communities, but the importance of neighboring ECM hosts is less well understood. To investigate the relative importance of host and neighborhood effects, we examined the ECM fungal communities associated with Alnus rhombifolia, a host of specific ECM fungi, and Betula occidentalis, a host of generalist ECM fungi. We hypothesized that the host-specific Alnus-associated ECM fungal community would not be susceptible to the influence of plant neighborhood, while the generalist Betula-associated community would. ECM fungal communities on both hosts were characterized using ITS sequences derived from conspecific and heterospecific host settings at a field site in western Idaho, USA, and from a growth chamber bioassay. In the field study, the Betula neighborhood added minor constituents to the Alnus ECM fungal community, while in the bioassay, late planting of Betula generated strong priority effects that allowed the established Alnus neighborhood to control the structure of the Betula community. Our results indicate that while host identity acts as a primary filter on the composition and diversity of ECM fungal communities, proximity to a closely related host can mediate significant changes in community structure.

Soil propagule banks of ectomycorrhizal fungi share many common species along an elevation gradient

“…Our results were similar to those of Collier and Bidartondo (2009), who documented high frequencies of Rhizopogon and Suillus on Pinus and of other taxa (i.e., Laccaria proxima, Thelephora terrestris, and Lactarius hepaticus) on Betula seedlings. In contrast, taxonomically related Betula and Alnus seedlings were demonstrated to harbor distinct EM fungal species (Bogar and Kennedy 2014). EM fungal communities in Alnus are usually low diverse and composed of unique host-specific EM fungi (i.e., Alpova and Alnicola), probably in relation to the simultaneous colonization of Alnus roots by EM fungi and nitrogenfixing bacteria (Kennedy and Hill 2010).…”

“…Some studies have used multiple host species in bioassays and found no significant host effect among several Pinus species at a continental scale (Glassman et al 2015) or between Pinus and Abies (Izzo et al 2006b). In contrast, EM fungal communities differed between Betula and Alnus bioassay seedlings, on which Alnus were associated with low diverse (i.e., three species) and specialist EM fungal taxa (i.e., Alpova and Alnicola; Bogar and Kennedy 2014). Moreover, frequently occurring fungal taxa differed between Betula and Pinus (Collier and Bidartondo 2009) and between Pinus and Pseudotsuga bioassay seedlings (Pickles et al 2015).…”

Alder and the Golden Fleece: high diversity of Frankia and ectomycorrhizal fungi revealed from Alnus glutinosa subsp. barbata roots close to a Tertiary and glacial refugium

“…Among fungi, two potential endemic species belong to a wind-dispersed genus ( Inocybe). Although species of Inocybe are regularly detected on alder roots (Bogar & Kennedy, 2013; Roy et al, 2013; Põlme et al, 2013), current knowledge on this genus is still too limited to determine if these Inocybe sp. are specific to Alnus or if their occurrence reflects a local adaptation to a particular habitat.…”

Mycorrhizal co‐invasion and novel interactions depend on neighborhood context

“…Multiple factors may have produced the observed differences in richness and composition across neighborhood contexts. First, adult trees act as a reservoir of fungal inoculum, which can then be transferred to establishing seedlings (Jones et al 1997, Bogar and Kennedy 2013. Second, large, established stands of mature trees may host distinct fungal communities compared to isolated trees (Peay et al 2010, Hynson et al 2013) and seedlings (Dickie and Reich 2005) due to differences in fungal dispersal (Peay et al 2010) and successional stage (Deacon et al 1983).…”

“…For example, few studies have identified the mycorrhizal associates of ectomycorrhizal trees invading into native forests. However, context may be important to invasion because neighboring ectomycorrhizal hosts can influence the ectomycorrhizal communities of seedlings, regardless of whether the neighboring host is of the same , Dickie and Reich 2005, Nara 2006 or of a different , Nara and Hogetsu 2004, Bogar and Kennedy 2013 species as the seedling. This neighborhood effect may be caused by an actively growing common mycorrhizal network (Fleming 1983, Newman 1988, Simard and Durall 2004 or by a soil spore bank (Ashkannejhad andHorton 2006, Collier andBidartondo 2009).…”