Effects of soil environmental changes accompanying soil erosion on the soil prokaryotes and fungi of cool temperate forests in Southern Japan

Soil erosion, which involves the degradation of the physical and chemical properties of soil, is a major threat to the soil environment. Although the effects of soil erosion on the physical or chemical properties of forests have been studied, little has been reported on the soil microbial community, which is likely to affect forest ecosystems. This study aimed to elucidate how the microbiome changed with the soil environment accompanying soil erosion in cool temperate mixed forests in Southern Japan, where soil erosion has been accelerated by the increased population of sika deer. We investigated the soil microbial communities of the different soil erosion intensities at three forest sites. In prokaryotic communities, diversity indices were increased with the sum of the height of exposed roots (SUMH), an index of soil erosion. In fungal communities, the relative abundances of plant pathogenic and wood saprotroph fungi were increased as SUMH increased and those of symbiotrophs and ectomycorrhizal fungi were increased with humus organic matter content, suggesting that the difficulties in establishing plants would be increased as soil erosion progressed because of the changes in the composition and function of fungal communities in eroded areas. Moreover, soil fungal communities had a more complex co-occurrence network than that of prokaryote, suggesting that the effects of soil erosion on fungal network is smaller than those on bacterial network. Changes in the soil environment induced by soil erosion altered the microbiomes in the deeper layers of the soil and had different effect on prokaryotes and fungi.