Change in soil fungal community structure driven by a decline in ectomycorrhizal fungi following a mountain pine beetle (Dendroctonus ponderosae) outbreak

Abstract

Summary Western North American landscapes are rapidly being transformed by forest die‐off caused by mountain pine beetle (Dendroctonus ponderosae), with implications for plant and soil communities. The mechanisms that drive changes in soil community structure, particularly for the highly prevalent ectomycorrhizal fungi in pine forests, are complex and intertwined. Critical to enhancing understanding will be disentangling the relative importance of host tree mortality from changes in soil chemistry following tree death. Here, we used a recent bark beetle outbreak in lodgepole pine (Pinus contorta) forests of western Canada to test whether the effects of tree mortality altered the richness and composition of belowground fungal communities, including ectomycorrhizal and saprotrophic fungi. We also determined the effects of environmental factors (i.e. soil nutrients, moisture, and phenolics) and geographical distance, both of which can influence the richness and composition of soil fungi. The richness of both groups of soil fungi declined and the overall composition was altered by beetle‐induced tree mortality. Soil nutrients, soil phenolics and geographical distance influenced the community structure of soil fungi; however, the relative importance of these factors differed between ectomycorrhizal and saprotrophic fungi. The independent effects of tree mortality, soil phenolics and geographical distance influenced the community composition of ectomycorrhizal fungi, while the community composition of saprotrophic fungi was weakly but significantly correlated with the geographical distance of plots. Taken together, our results indicate that both deterministic and stochastic processes structure soil fungal communities following landscape‐scale insect outbreaks and reflect the independent roles tree mortality, soil chemistry and geographical distance play in regulating the community composition of soil fungi.

Soil Fungal Community in Norway Spruce Forests under Bark Beetle Attack

“…The only study that has dealt with a bark beetle outbreak in spruce forest reported a decrease in mycorrhizal fungi while saprotrophic fungi increased due to the higher mass of dead plant material and gradual changes in the fungal community drive by substrate availability [16]. Similar observations were made by Treu et al [17] and Pec et al [18] in pine forests destroyed by mountain pine beetle in Canada.…”

Changes of Scots Pine Phyllosphere and Soil Fungal Communities during Outbreaks of Defoliating Insects

“…This finding is in line with the results of an artificial defoliation experiment in Scots pine by Kuikka et al [25] reporting reduced production of sporocarps as well as reduced diversity in ectomycorrhizal fungi under defoliated trees (see also [28,29,32]). For example, in lodgepole pine (Pinus contorta Dougl.…”

“…latifolia Engelm.) pine beetle (Dendroctonus ponderosae Hopkins) outbreaks led to a decline in species richness [32] as well as in the abundance of ectomycorrhizal fungi [29]. Bark beetle outbreaks in Norway spruce stands also reduced ectomycorrhizal fungi, but increased saprophytic fungi [28].…”

“…The effects of outbreaks of single pests either on phyllosphere or soil microbial communities have been studied already (e.g., [21,24,[27][28][29][30][31][32][33][34][35]), but these data did not simultaneously compare the effect of pest outbreaks on phyllosphere and soil microbial communities and did not differentiate between the effects of different pest insects in the same forest ecosystem. Here, we analyzed the effect of outbreaks of two defoliating insects, nun moth or pine tree lappet, in Scots pine stands in eastern Germany on the bacterial and fungal community structure in the soil and the phyllosphere using DGGE.…”

Arable agriculture changes soil microbial communities in the South African Grassland Biome

“…2,9,[13][14][15] In contrast, the differences found in the composition and pattern of the fungal communities between the two habitats were better explained by calcium (R=0.019, p=0.01) and phosphorus (R=0.01, p=0.004) concentrations (Supplementary figure 7), and corroborated previous studies. 9,58 In summary, our results have shown that bacterial and fungal communities were significantly influenced by land-use changes, with agricultural soils containing distinct bacterial and fungal communities compared with natural grassland soils. Natural grassland soils consistently exhibited higher numbers of OTUs than did agricultural soils.…”