A continental view of pine‐associated ectomycorrhizal fungal spore banks: a quiescent functional guild with a strong biogeographic pattern

Abstract

SummaryEcologists have long acknowledged the importance of seed banks; yet, despite the fact that many plants rely on mycorrhizal fungi for survival and growth, the structure of ectomycorrhizal (ECM) fungal spore banks remains poorly understood. The primary goal of this study was to assess the geographic structure in pine-associated ECM fungal spore banks across the North American continent.Soils were collected from 19 plots in forests across North America. Fresh soils were pyrosequenced for fungal internal transcribed spacer (ITS) amplicons. Adjacent soil cores were dried and bioassayed with pine seedlings, and colonized roots were pyrosequenced to detect resistant propagules of ECM fungi.The results showed that ECM spore banks correlated strongly with biogeographic location, but not with the identity of congeneric plant hosts. Minimal community overlap was found between resident ECM fungi vs those in spore banks, and spore bank assemblages were relatively simple and dominated by Rhizopogon, Wilcoxina, Cenococcum, Thelephora, Tuber, Laccaria and Suillus.Similar to plant seed banks, ECM fungal spore banks are, in general, depauperate, and represent a small and rare subset of the mature forest soil fungal community. Yet, they may be extremely important in fungal colonization after large-scale disturbances such as clear cuts and forest fires.

Ectomycorrhizal fungal spore bank recovery after a severe forest fire: some like it hot

“…These samples were sieved through 2-mm mesh to remove roots and rocks, homogenized by hand and air dried to kill active vegetative fungal hyphae (Taylor and Bruns, 1999). Hereafter, we refer to these as spore bank bioassays (Bonito et al, 2012;Glassman et al, 2015). Five replicates each of P. ponderosa and P. muricata were planted in separate 50-ml Conetainers (Super 'Stubby' Cell Cone-tainer; Stuewe & Sons Inc., Tangent, OR, USA) in soils from each of the 26 sampling locations.…”

“…Five replicates each of P. ponderosa and P. muricata were planted in separate 50-ml Conetainers (Super 'Stubby' Cell Cone-tainer; Stuewe & Sons Inc., Tangent, OR, USA) in soils from each of the 26 sampling locations. After 6 months, ECM fungal root tips were harvested and sequenced with 454 pyrosequencing (Glassman et al, 2015).…”

“…We measured soil moisture from all soils following air drying to ensure negligible water content (Supplementary Methods S4). Although pre-fire bioassays of plots CA1 and CA2 included P. ponderosa and P. muricata as hosts, no significant difference in retrieved communities was found by the two hosts (Glassman et al, 2015). However, P. muricata is easier to work with because unlike P. ponderosa, it does not require a long stratification to germination.…”

“…However, P. muricata is easier to work with because unlike P. ponderosa, it does not require a long stratification to germination. In addition, P. muricata was found to be the best bioassay host to maximize recovery of ECM spore bank taxa across North America (Glassman et al, 2015). For these reasons, our post-fire bioassays used only P. muricata.…”

“…We had the opportunity to study this fire because two of our long-term study plots were located within the fire perimeter. In both plots, we had exceptionally highquality pre-fire data on the composition of the soil fungal community, the resident root community and the ECM fungal spore bank community (Talbot et al, 2014;Glassman et al, 2015).…”