Diversity of corticolous myxomycetes in the last glacial refugia of Cryptomeria japonica in Japan

Abstract

<em>Cryptomeria japonica</em>, commonly known as Japanese cedar, is now widely distributed from glacial refuges to the entire Japanese archipelago, after the last ice age. The bark surface provides a habitat for many corticolous myxomycetes. Although corticolous myxomycetes are known to prefer tree species, the association between myxomycete distribution and host tree (<em>C. japonica</em>) divergence across the refuges has not been investigated. In this study, myxomycete communities in five refuges were assessed and compared with those in 14 peripheral areas. Bark samples were collected from at least 10 trees per site and were subjected to the moist chamber culture method (10 Petri dishes per tree) to examine the myxomycete fruiting bodies strictly. Environmental variables such as geographical location, climate condition, and bark traits (tree size, bark pH, and electric conductivity) were measured. Fruiting bodies appeared in 91% of the cultures, and 32 taxa (31 species and one varie ty) were recorded. Comparison of the communities between refuges and peripheral sites showed six myxomycete species, Arcyria cinerea, <em>Macbrideola argentea</em>, <em>Cribraria minutissima</em>, <em>Clastoderma debaryanum</em>, <em>Physarum viride</em> and <em>Physarum pusillum</em>, were significantly more abundant in the refuges and these communities preserved higher species diversity. By nonmetric multidimensional scaling, the communities in the Pacific side and the Sea of Japan side were ordered based on snow cover depth, in a pattern similar to the phylogenetic distribution of the host tree. Myxomycete groups were identified in the northern region, the Sea of Japan region, and the southern region (including Yakushima Island) of Japan. Thus, the refugial tree populations preserved the myxomycete species diversity on their bark and functioned as an important hotspot for myxomycetes. The distribution of corticolous myxomycetes was associated with the diversification and biogeographical distribution history of their host tree, <em>C. japonica</em>.

Association between corticolous myxomycetes and tree vitality in <i>Cryptomeria japonica</i>

“…A previous nationwide study found 30 species (including varieties) of myxomycetes on the bark of C. japonica trees (n = 188, Takahashi et al, 2018 ) and another study found 28 species (n = 176, Takahashi & Harakon, 2018 ). The most abundant species were P. rigida > C. confusa > E. berkeleyanum .…”

“…The most abundant species were P. rigida > C. confusa > E. berkeleyanum . The bark of C. japonica trees generally retains strong acidic condition, such as average pH with standard deviation of 3.7 ± 0.3 ( Takahashi et al, 2018 ) and 3.7 ± 0.2 ( Takahashi & Harakon, 2018 ). In the present study, slightly less acidity was observed on the bark, that is, the average pH was 3.9 ± 0.3 (n = 74) and ranged from 3.3 to 4.6.…”

“…Most trees were sampled twice, and a few additional trees were sampled in 2018. A previous study indicated that the species richness of corticolous myxomycetes at a site was saturated within a 10-tree sampling effort ( Takahashi & Harakon, 2018 ). The bark fragments of each sampled tree were completely stripped manually at approximately 800 cm 2 (approximately 50 g of dry weight) around the trunk surface at 0.5-2.0 m above the ground level, excluding the epiphytes.…”