Testing the link between community structure and function for ectomycorrhizal fungi involved in a global tripartite symbiosis

Abstract

SummaryAlnus trees associate with ectomycorrhizal (ECM) fungi and nitrogen-fixing Frankia bacteria and, although their ECM fungal communities are uncommonly host specific and species poor, it is unclear whether the functioning of Alnus ECM fungal symbionts differs from that of other ECM hosts.We used exoenzyme root tip assays and molecular identification to test whether ECM fungi on Alnus rubra differed in their ability to access organic phosphorus (P) and nitrogen (N) when compared with ECM fungi on the non-Frankia host Pseudotsuga menziesii.At the community level, potential acid phosphatase (AP) activity of ECM fungal root tips from A. rubra was significantly higher than that from P. menziesii, whereas potential leucine aminopeptidase (LA) activity was significantly lower for A. rubra root tips at one of the two sites. At the individual species level, there was no clear relationship between ECM fungal relative root tip abundance and relative AP or LA enzyme activities on either host.Our results are consistent with the hypothesis that ECM fungal communities associated with Alnus trees have enhanced organic P acquisition abilities relative to non-Frankia ECM hosts. This shift, in combination with the chemical conditions present in Alnus forest soils, may drive the atypical structure of Alnus ECM fungal communities.

In situ mycorrhizal function – knowledge gaps and future directions

“…Other examples of papers that have linked function and composition include Walker et al . (), which measured enzyme activities of individual EM root tips coupled with molecular analyses to identify the fungus involved, and Clemmensen et al . (), which combined high throughput sequencing and observations of EM fungal growth forms and decomposability to help explain shifts in carbon and nitrogen sequestrations along a boreal chronosequence.…”

Ectomycorrhizae and tree seedling nitrogen nutrition in forest restoration

“…Red alder (Alnus rubra Bong.) had only 25 % of the number of ECM fungal species found on sympatric Douglas-fir but the alder ECM fungal community had significantly higher P potential enzyme activities (Walker et al 2014). Perhaps chronic N deposition on forests over the long term will select for ECM fungi with high P acquisition ability.…”

“…As an interesting aside, alders (Alnus spp. ), N-fixing, ECM trees with abundant N provided by their symbiont, Frankia, have a species-poor but highly hostspecific ECM fungal community with high organic P acquisition ability (Walker et al 2014). Red alder (Alnus rubra Bong.)…”

Plant Microbes Symbiosis: Applied Facets

“…As far as the fungal part is concerned, the majority of ECM fungi belong to Basidiomycetes , which can form macroscopic epigeous fruiting bodies that often grow next to tree trunks in woodlands, such as Boletus edulis and Cantharellus cibarius , while some others belong to Ascomycetes and form hypogeous fruiting bodies, such as truffl es (Girlanda et al 2007 ). Interestingly, when a tripartite interaction is present, as in the Alnus host system (N-fi xing bacteria, ECM fungi, Alnus roots), the ECM fungal activity seems to be shifted toward a greater capacity for organic P acquisition (Walker et al 2013 ). In line with these observations, Averill et al ( 2014 ) and the relative commentary by Bradford ( 2014 ) have suggested that the presence of greater stores of organic matter in forest soils dominated by ECM fungi, than in those dominated by arbuscular mycorrhizal (AM) fungi, could be due to a reduced nitrogen availability for the free-living microbes that use organic matter.…”