Ectomycorrhizal fungi in association with Pinus sylvestris seedlings promote soil aggregation and soil water repellency

Research on fungal effects on soil aggregation has been heavily biased towards arbuscular mycorrhiza. Even though ectomycorrhizal fungi are thought to be as important as arbuscular mycorrhizal fungi and saprotrophic fungi in contributing to soil structure, there are few experimental studies on this topic. Here we quantified how nine ectomycorrhizal fungi in association with Pinus sylvestris seedlings affected soil aggregation and soil water repellency (SWR) of a sandy loamy soil. Water-stable aggregates (>0.25 mm diameter) increased by 6–12% when plants were associated with Laccaria bicolor, Laccaria laccata, Lactarius theiogalus, Paxillus involutus and Suillus bovinus. Mean weight diameter (MWD) of soil aggregates also increased, primarily in the 2–4 mm diameter size class. However, Suillus granulatus increased water-stable aggregates but not MWD, conversely Rhizopogon roseolus and Suillus luteus increased MWD but not water-stable aggregates. We also found Lt. theiogalus, R. roseolus and S. luteus promoted SWR. Furthermore, hyphal length was weakly correlated with MWD (R = 0.27, P