Soil Fungal Community in Norway Spruce Forests under Bark Beetle Attack

Abstract

Bark beetle infestation is a widespread phenomenon in temperate forests, which are facing significant weather fluctuations accompanying climate change. Fungi play key roles in forest ecosystems as symbionts of ectomycorrhizal trees, decomposers, or parasites, but the effect of severe disturbances on their communities is largely unknown. The responses of soil fungal communities following bark beetle attack were determined using Illumina sequencing of soil samples from 10 microsites in a mature forest not attacked by bark beetle, a forest attacked by bark beetle, a forest destroyed by bark beetle, and a stand where all trees were removed after a windstorm. The proportion of ITS2 sequences assigned to mycorrhizal fungal species decreased with increased intensity of bark beetle attack (from 70 to 15%), whereas the proportion of saprotrophs increased (from 29 to 77%). Differences in the ectomycorrhizal (ECM) fungal community was further characterized by a decrease in the sequence proportion of Elaphomyces sp. and Russula sp. and an increase in Piloderma sp., Wilcoxina sp., and Thelephora terrestris. Interestingly, the species composition of the ECM fungal community in the forest one year after removing the windstorm-damaged trees was similar to that of the mature forest, despite the sequence proportion attributed to ECM fungi decreased.

Ectomycorrhizal Community on Norway Spruce Seedlings Following Bark Beetle Infestation

“…On the other hand, the ECM species community composition on Norway spruce seedlings changed, which was consistent with our hypothesis. When comparing this alteration with one detected in a soil fungal community after bark beetle infestation [20], where Elaphomyces Nees sp. and Russula spp.…”

“…T. fibrillosa occupied twice as many seedlings in K2 than in REF, while C. geophilum showed an opposite trend. REF was characterized by the presence of Lactarius, Russula, and Cortinarius species, associated with healthy forests [20,36,37], with some were still found in K1. A similar trend was detected by Peter et al [33], who found T. fibrillosa increased its abundance on seedlings in a locality affected by air pollution with increasing damage intensity, while Russula and Lactarius species preferred sites with lower damage levels.…”

“…The resulting fungal species composition could influence the plant successional trajectory, which may, in turn, govern the fungal successional trajectory.Above-ground herbivory by bark beetle affects ECM symbioses by reducing the carbon flow to the roots and fungal symbionts [15,16]. ECM colonization is usually not reduced, but the fungal composition is changed in favor of ECM morphotypes with low demands on photosynthates [17][18][19][20], which may affect the nutrient uptake and recovery of the host [21].The Tatra Mountains (Slovakia) were affected by a serious windstorm in 2004, which destroyed about 12,600 ha of mountain spruce forest [22]. Following this historically largest calamity in the region, bark beetle started to spread in the surrounding spruce forest in 2007 and 2008 [23].…”

“…in originally unmanaged spruce forest with larch admixture (Lariceto-Piceetum) on cambisols or podzosol with granodiorite or moraine bedrock [23,24]. Before the bark beetle attack, the forest was 130-140 years old, spruce accounted for 80 to 90%, and canopy cover reached from 45 to 60% [20,23,24].The K1 forest type is a forest attacked by bark beetle, with 10% dead tree crown projection in 2015. The bark beetle infestation started to spread in 2009.…”

“…Above-ground herbivory by bark beetle affects ECM symbioses by reducing the carbon flow to the roots and fungal symbionts [15,16]. ECM colonization is usually not reduced, but the fungal composition is changed in favor of ECM morphotypes with low demands on photosynthates [17][18][19][20], which may affect the nutrient uptake and recovery of the host [21].…”