Epsilon Archive for Student Projects

Abstract

Ongoing global change and forestry practices are increasing stress on boreal forest ecosystems, making them more susceptible to insect infestations. In Sweden, outbreaks of the spruce bark beetle (Ips typographus) have become more frequent, leading to increased infestation levels in spruce (Picea abies) stands. These disturbances in aboveground vegetation may profoundly affect soil fungi, particularly the symbiotic relationship between trees and ectomycorrhizal fungi, which play key roles in boreal soil nutrient and carbon cycles, potentially affecting ecosystem processes.

Soil samples of organic horizons were collected from twelve spruce stands in the region surrounding Uppsala, Sweden, in a paired setup, where infested sites showed different infestation vulnerabilities, measured on the ratio of infested to total spruces. In contrast, nearby paired control sites showed no sign of infestation. I introduced the term “infestation vulnerability” to compare the infestation intensity of infested sites to the paired un-infested control sites. The impact of infestation on fungal community composition was assessed using DNA sequencing of the ITS2 and LSU regions, focusing on shifts in the relative abundance of fungal guilds between infested and control sites and along infestation vulnerability.

Ectomycorrhizal fungi were significantly less in relative abundance at bark beetle-infested sites compared to un-infested control sites, while saprotrophic fungi showed the opposite pattern. Along with increasing infestation vulnerability, ECM fungi declined in relative abundance, whereas saprotrophs increased. Interestingly, the abundance of ECM fungi in non-infested control sites increased with the level of infestation observed in their paired infested sites. Soil properties at both site types correlated with the infestation vulnerability, suggesting decreased soil fertility, possibly making trees susceptible to bark beetle infestation and their outbreaks more pronounced. At the same time, ECM fungi increase due to a higher need of trees for symbiotic support.