Rapid shift of soil fungal community compositions after clear-cutting in hemiboreal coniferous forests

Abstract

Clear-cutting is the main forest management method in boreal and hemiboreal forests, but recently its implementation has raised concerns due to its effects on biodiversity, including the soil fungal biota. Forest soil fungi have an important role as mycorrhizal symbionts, decomposers of organic material and root pathogens. There is conflicting information about the effect of clear-cutting and related management practices on fungal assemblages. We aimed to assess the factors that affect the assemblages of major fungal functional guilds (ectomycorrhizal, saprotrophic, pathogenic and yeast fungi) and the changes in soil fungal diversity and community composition after clear-cutting in Norway spruce and Scots pine (retention trees > 5 m3 per ha) stands, and compared the outcomes with alongside control sites (uncut stands). In addition, we tested the effect of the size of the clear-cut area, soil scarification and the forest regeneration method (planting and sowing) on soil fungi. The samples were collected from 50 different clear-cut sites and 50 control sites on two repeated sampling occasions: recently (0–6 months) cut and one year after clear-cutting. Based on high-throughput Illumina sequencing soil fungal communities were affected immediately after clear-cutting, resulting in significantly different fungal structure composition. Soil fungal diversity in both spruce and pine stands increased after one year post-cut compared to control sites, except the richness of ectomycorrhizal fungi in spruce sites. However, the fungal communities showed the highest similarity between control and one year post-cut sites based on principal coordinates (PCO) and Permanova analyses. Nonetheless, relative abundance of ectomycorrhizal (EcM) fungi declined, whereas that of saprotrophs and pathogens increased. In spruce sites, saprotrophic fungi were negatively affected by soil scarification, but this was not evident in pine sites. Forest regeneration by planting after clear-cutting in pine sites resulted in higher ectomycorrhizal fungal richness compared to sowing. Size of the clear-cut area (ranging from 0.4 to 3.1 (5.0) ha) did not affect soil fungal diversity in spruce- and pine-dominated sites. We demonstrated that fungal community composition may recover within one year after clear-cutting in pine- and spruce-dominated hemiboreal forest stands. However, understanding the long-term effects of management on patterns and shifts in fungal biota needs a long-term study.