Myxomycete diversity on Cryptomeria japonica bark varies with land-use type along montane rivers

Myxomycetes occur globally, but little is known about the mechanism by which myxomycete diversity and community structure respond to environmental gradients and human activity at local scales. The present study assessed the distribution of corticolous myxomycetes living on the bark of <em>Cryptomeria japonica</em> trees along three rivers originating in the Chugoku Mountains in western Japan. Bark samples were collected from 14 sites along each river, which encompass the river sources as well as the upper, middle, and lower reaches. The environmental characteristics of each site were assessed for three variable types: geography, climate, and land-use. A 1 km2 grid was superimposed onto each survey site, consisting of 100 cells of 1 ha each, and each cell was classified using aerial imagery into a broad land-use type. Of these, three land-use types (forest, farmland, and residential) were regularly used as a comprehensive indicator of landscape. The bark samples were cultured using the moist chamber technique, and the resulting myxomycete fruiting bodies were identified. Sporophores formed on 96% of the 1,490 moist chamber cultures and were classified into 27 taxa (26 species and one variety). Species diversity was highest in natural forests near river sources and decreased with proximity to downstream estuaries. Community similarities between survey sites were analysed using non-metric multidimensional scaling (NMDS). The first NMDS axis was negatively correlated with distance from estuary and forest coverage. Indicator species were identified for environmental changes along river basins. The relative abundances of <em>Macbrideola argentea</em>, <em>Hemitrichia velutina</em>, and <em>Physarum nutans</em> var. <em>rubrum</em> were positively correlated with forest coverage. In contrast, the relative abundances of <em>Clastoderma debaryanum</em>, <em>Diderma chondrioderma</em>, and <em>Echinostelium minutum</em> were positively correlated with residential area coverage. The distribution of corticolous myxomycetes on C. japonica trees was associated with local landscape changes along the river environments. This is the first report on myxomycetes assemblages along river basins (acting as ecological corridors) and indicates that forest degradation and land-use types strongly affect myxomycete diversity on the bark of living <em>C. japonica</em> trees.