Saprotrophic potential of ectomycorrhizal fungi in spruce forest
ecosystems
Lori A. Phillips, Melanie D. Jones
Biology and Physical Geography Unit, UBC Okanagan, Kelowna, BC, Canada
Introduction
Ectomycorrhizal (EcM) fungi are common denizens of coniferous
forests. There is an ongoing discussion as to whether EcM fungi
contribute directly to soil organic matter (SOM) turnover in these
ecosystems. Ingrowth bags used to trap EcM extramatrical hyphae
are typically made with silica sand in order to exclude hyphae from
obligate saprotrophs. The same lack of organic material which limits
saprotroph colonization however, also prevents the expression of
extracellular enzymes involved in SOM turnover. To address this
issue, we used mesh bags filled with organic material and
surrounded by a barrier of silica sand to capture EcM hyphae in a
spruce forest. The saprotrophic potential of this EcM mycelia was
compared to that of community (EcM and other) mycelia from bags
with no sand barrier and from the adjacent forest floor.
Results
 Enzyme activity in organic substrates
Table 1. Enzymes used to assess decomposition activity
Enzyme
Cellobiohydrolase
β -glucosidase
β-N-acetylglucosaminidase
Phosphatase
Sulfatase
Xylosidase
Laccase
Abbrev.
CEL
GLU
NAG
PHO
SUL
XYL
LAC
General Role
Cellulose degradation
Cellulose degradation
Chitin degradation
Phosphate mobilization
Hydrolyzes sulphate esters
Hemicellulose degradation
Lignin degradation
Objectives
  To assess the efficacy of a novel system for capturing
enzymatically active EcM hyphae
  To assess the contribution of EcM hyphae to SOM turnover
in forest ecosystems
Figure 1. Average enzymatic activity of all substrates
Data presented as means (n=9), error bars indicate 1 SD, *mmol h-1 g-1
 Identification of fungal communities
Experimental design and methods
Spruce forest site:
 BC Ministry of Forests long term research site, Sub-Boreal Spruce
Biogeoclimatic Zone, zonal Sxw–Huckleberry vegetation
EcM extramatrical hyphal capture:
 Dominant EcM tips identified in FF substrate
 Piloderma, Cenococcum, Amphinema, Cortinarius, Tylospora,
and Wilcoxina spp.
 ~20,000 trimmed fungal ITS1 amplicons identified in
each +S, -S, and FF sample (n=9 each)
 50µm mesh bags filled with site-specific fermentation-humus
organic material (gamma irradiated, 2x3 Mrad)
 +S: mesh bags with sand barrier (≥1cm)
 -S: mesh bags with no sand barrier
 +S and -S buried in forest floor layer of fertilization plots at spruce
site (n=9, with 5 sub-replicates per plot)
 Organic material from +S, -S and from adjacent forest floor (FF)
sampled after one growing season
Figure 2. Species distribution of ITS1 amplicons in
composited samples (~200,000 amplicons each)
Enzymatic activity
 Microplate assays of samples (+S, -S, and FF organic material, and
sand) using fluorogenic or colourimetric substrates (Table 1)
Summary and conclusions
Identification of fungal communities
 Sanger sequencing of dominant EcM tips in FF substrate
 Tag-encoded 454 sequencing of the ITS1 region of all substrates
 Quality screened and trimmed sequences clustered using CDHit; representative sequences identified via NCBI Blast search
Results
 Hyphal colonization after one growing season
Fungal communities from mesh bags surrounded by a sand barrier
were predominantly ectomycorrhizal, with a large proportion of
medium-distance explorer-types (ie Amphinema spp.). In contrast,
mesh bags with no sand barrier had a large proportion of obligate
saprotrophic fungi (ie Mortierella spp.). These differences in
community structure did not result in significant differences in the
activity of enzymes involved in soil organic matter (SOM)
breakdown. This finding indicates that ectomycorrhizal
extramatrical hyphae may be important contributors to SOM
turnover in forested ecosystems.
 Sand barriers effectively excluded obligate saprotrophic fungi
from substrate-filled mesh bags and allowed for the isolation of
EcM hyphae, which expressed enzymes involved in SOM turnover
Acknowledgements: Forest research sites established by R. Brockley,
BC Ministry of Forests; Containers donated by NetPak, Coquitlam, BC
Lori Phillips: [email protected]