Ectomycorrhizal Fungal Responses to Forest Liming and Wood Ash Addition: Review and Meta-analysis

Abstract

Large-scale liming and wood ash addition are common practices to mitigate soil and water acidification in temperate and boreal forests. In addition, wood ash recycles nutrients removed at harvest to the forest ecosystem. Both liming and wood ash applications typically increase soil pH by 1–2 units. Therefore, they affect a range of soil processes and organisms including ectomycorrhizal (EM) fungi which are vital for the nutrition of many tree species. Here we review field studies reporting the effects of lime and wood ash amendments on EM fungi. We systematically compiled studies where known amounts of ash or lime were distributed to plots paired with comparable control plots, and where mycorrhizal variables were recorded. For a subset of studies meeting explicit criteria, we performed meta-analyses using overall mycorrhizal abundance, species richness or the abundance of specific fungal taxa as response variables. Guided by availability of data, the focus is on Nordic coniferous forests. Although the reviewed field studies varied widely in dosage and experimental setup they clearly demonstrated that liming and wood ash amendments influence EM fungal species composition. Across studies, species belonging to the lineages Cortinarius and Russula-lactarius (Basidiomycota), particularly Russula ochroleuca, decreased in relative abundance, while species within the Tuber-helvella (Ascomycota) increased. Particular species within the Amphinema-tylospora lineage responded in opposite directions; Tylospora fibrillosa decreased in relation to the control, while Amphinema byssoides increased. The significant changes in species or clade abundances were in the range of 5–20% compared to non-treated plots. In contrast, neither the belowground mycorrhizal biomass nor species richness responded to liming or wood ash applications. We conclude that liming and wood ash amendments cause consistent EM fungal species dominance shifts, but that a high EM fungal biomass and species and phylogenetic richness is maintained on the tree roots. Given the large dispersal potential of many EM fungi, we therefore suggest that these treatments at normal recommended dosages do not pose any immediate threats to EM fungal biodiversity, at least not when applied at relatively small spatial scales. Whether the observed dominance shifts among EM fungal clades have consequences for the functioning of the EM fungal guild, e.g. in relation to nutrient cycling or tree nutrition, is an important question that should be further investigated.