Search

Wood-inhabiting fungi are critically important for the decomposition of coarse woody debris (CWD). To evaluate the relative importance of climate, vegetation, and spatial factors in the functional composition of fungal communities that inhabit CWD in discontinuously distributed subalpine Hondo spruce (Picea jezoensis (Sieb. & Zucc.) Carr. var. hondoensis (Mayr) Rehder) forests, a metabarcoding analysis was conducted on spruce deadwood samples obtained from six subalpine forests in central Japan using a high-throughput DNA sequencing technique. We detected 454 fungal operational taxonomic units (OTUs) from 67 spruce CWDs and determined that spatial factors explained a larger fraction of community variation than environmental (climate and vegetation) factors at all six study sites. However, environmental factors explained a larger fraction than spatial factors if we excluded data from one site that is geographically distant from other study sites. The OTU number and the occurrence of brown-rot fungi were positively associated with mean annual temperature and negatively associated with mean annual precipitation. Similarly, the principal component of forest vegetation significantly affected the OTU number and occurrence of brown-rot fungi. Precipitation seasonality was positively associated with the OTU number of undefined saprotrophs. These results suggest that fungal OTUs belonging to different functional groups respond differently to environmental variables.

Picea is one of the most dominant conifer genera in the Northern Hemisphere and includes species which require coarse woody debris (CWD) as a seedbed for regeneration. To understand the future of forest distribution under global climate change, it is important to investigate regeneration mechanisms in Picea forests on the borders of its distribution. In the present study, we evaluated the biotic factors affecting the establishment of Picea jezoensis var. hondoensis seedlings on CWD in one of its southernmost populations in central Japan, where there is dieback of Picea forest. Amplicon sequencing of the fungal ITS1 region of rDNA obtained from wood samples showed that forest dieback increased the frequency of brown rot fungi in CWD. The frequency of brown-rotted wood, in which wood holocellulose is decayed, increased with dieback intensity. The domination of brown-rotted wood in dieback forests was negatively associated with bryophyte cover which was positively associated with Picea seedling density. Forest dieback itself also had other strong negative effects on bryophytes. Thus, linkages between dead wood and spruce seedlings via bryophytes had collapsed after the dieback event, which may partly be a reason that the spruce forest shifted to and is staying as open grassland.

The biodiversity–ecosystem function relationship is a central topic in ecology. Fungi are the dominant decomposers of organic plant material in terrestrial ecosystems and display tremendous species diversity. However, little is known about the fungal diversity–decomposition relationship. We evaluated fungal community assemblies and substrate quality in different stages of wood decay to assess the relationships between fungal species richness and weight loss of wood substrate under laboratory conditions. Wood-inhabiting fungal communities in the early and late stages of pine log decomposition were used as a model. Colonisation with certain species prior to inoculation with other species resulted in four-fold differences in fungal species richness and up to tenfold differences in the rate of wood substrate decomposition in both early- and late-decaying fungal communities. Differences in wood substrate quality had a significant impact on species richness and weight loss of wood and the relationships between the two, which were negative or neutral. Late communities showed significantly negative species richness–decay relationships in wood at all decay stages, whereas negative relationships in early communities were significant only in the intermediate decay stage. Our results suggest that changes in fungal communities and wood quality during wood decomposition affect the fungal diversity–decomposition relationship.

Storm disturbance has a huge impact on subalpine forest ecosystems. Evaluating the long-term effects and mechanisms of storm disturbance is of great significance for conservation of subalpine forests as frequency and intensity of storms are increasing because of the climate change. Species of subalpine conifer tree genera such as Picea and Tsuga need coarse woody debris (CWD) such as logs and stumps for seedling colonization; thus, their establishment is greatly affected by the condition of CWD, which largely depends on the activity of fungal decomposer communities and saproxylic bryophyte communities. Because the process of CWD decay and associated ecological succession is known to take several decades in subalpine forests, we hypothesized that storm disturbance has long-lasting effects on fungal communities, their wood decay function, saproxylic bryophyte communities, and seedling establishment. To test this hypothesis, we surveyed fungal, bryophyte, and seedling communities at forest sites that had been disturbed by a large typhoon 55 years ago and compared them with those of surrounding undisturbed coniferous forest in central Japan. Contrary to our hypothesis, Illumina sequencing for the fungal ITS1 region in rDNA obtained from wood samples did not show that past disturbance had an obvious effect on current fungal communities. Also, the frequencies of occurrence of various wood decay types were not significantly different between disturbed and undisturbed plots. However, disturbance affected bryophyte communities, which had strong effects on the seedling densities of Picea jezoensis var. hondoensis, Tsuga diversifolia, and Betula spp. These results suggest that the previous typhoon disturbance in the focal area had long-lasting effects on biotic interactions and seedling regeneration on CWD, but these effects might not be attributable to the impacts of disturbance on CWD fungal communities and their wood decay function.

Rhytismataceous fungi (Ascomycota) exhibit ligninolytic activities during the initial stages of litter decomposition. We quantitatively investigated the geographical distributions of rhytismataceous fungi on Camellia japonica leaf litter across Japan. We found three rhytismataceous species ( Coccomyces sp., Lophodermium jiangnanense , and a Rhytismataceae sp.) on bleached leaves of C. japonica . The Coccomyces sp. was distributed at all 40 sites investigated. On the other hand, L. jiangnanense was restricted to the southwestern region, and the Rhytismataceae sp. was localized to part of the warm-temperate zone. L. jiangnanense and the Rhytismataceae sp. were more common at sites with higher annual temperatures and greater precipitation. The relative abundance of rhytismataceous fungi revealed that either Coccomyces sp. or L. jiangnanense predominated at all sites, with a distribution related to annual precipitation. These results suggest that the geographical distributions and abundances of rhytismataceous fungi are influenced by climatic conditions.

In forest communities, conspecific density/distance dependence (CDD) is an important factor regulating diversity. It remains unknown how and the extent to which gap creation alters the mode and strength of CDD via changes in the relative importance of pathogens and mycorrhizae. Seeds of two hardwoods (i.e., Acer mono associated with arbuscular mycorrhizae [AM] and Quercus serrata associated with ectomycorrhizae [EM]) were sown reciprocally at four distances from the boundary between Acer- and Quercus-dominated forests towards forest interior in each of forest understories (FUs) and gaps. The causes of seed and seedling mortality, seedling growth and colonization of mycorrhizal fungi were investigated. In Acer, seed and seedling mortality were highest in Acer forests and gradually decreased towards the interior of Quercus forests in FU, mainly due to severe attack of soil pathogens, invertebrates, and leaf diseases. The reverse was true in gaps, due to reduction of damping-off damage caused by distance-dependent colonization of AM. In Quercus, most seeds and seedlings were eaten by vertebrates in FUs. The seedling mortality caused by leaf diseases was not high, even beneath conspecific forests with higher colonization of EM in gaps, suggesting a positive EM influence. In both species, seedling mass was greatest in conspecific forests and gradually decreased towards the interior of heterospecific forests in gaps, due to higher colonization of mycorrhizae near conspecifics. In conclusion, light conditions strongly altered the mode of CDD via changes in relative influence of pathogens and mycorrhizae, suggesting that gap creation may regulate species diversity via changes in the mode of CDD.

Thinning is an effective method to create mixed hardwood-conifer forests, as it results in successful hardwood recruitment. However, it remains unclear to what extent mycorrhizal association (AM, or arbuscular mycorrhizae vs. ECM, ectomycorrhizae) affects hardwood recruitment. In this study, we explored which hardwood mycorrhizal type was more advantageous to recruit into a Cryptomeria japonica (AM conifer) plantation. We compared seedling recruitment success (i.e. seedling emergence, survival, and growth) between AM and ECM hardwoods during five years after thinning at various levels: 67% thinned (intensive), 33% thinned (weak) and un-thinned treatments (control). We also investigated the percent colonization of mycorrhizal fungi for the seedlings of the most dominant AM (Cornus controversa) and ECM (Quercus serrata) hardwoods in both the C. japonica plantation and an adjacent forest dominated by ECM tree species (e.g. Q. serrata, Alnus hirsuta var. sibirica, Castanea crenata). During the five years, seedling emergence and survival were greater in AM than ECM for most of the different emergence cohorts, resulting in a greater number of individuals for AM rather than ECM hardwoods for all thinning intensities. Vertical growth of the seedlings was also greater for AM than ECM species, particularly for early emerging cohorts in both the weak and intensive treatments. Percent colonization of AM fungi to AM seedlings was greater in the AM conifer plantation than in the adjacent ECM-dominant forest. In contrast, percent colonization of ECM fungi to ECM-type seedlings was lower in the plantation compared to the adjacent forest. These results suggest that AM hardwoods could easily be recruited to AM conifer plantations, probably due to the fact that AM-type seedlings could easily become associated with AM fungi in the same mycorrhizal-type plantation. Growth of the AM seedlings was enhanced, which was likely to be due to the sharing of AM fungi, which translocate nutrients via hyphal networks. In contrast, recruitment of ECM-type seedlings was strongly inhibited, probably due to the lack of colonization of the ECM fungi in the AM-type plantation. This study demonstrates that mycorrhizal associations play an important role in recruitment success of hardwoods into AM conifer plantations. Thus, when forest managers intend to convert conifer plantations to mixed hardwood and conifer forests, they should consider the role of mycorrhizal fungal type in future species composition.

(137)Cs concentrations in ten species of foliose lichens collected within Tsukuba-city in August 2013 ranged from 1.7 to 35 kBq/kg. The relationships between (137)Cs in two dominant species, Dirinaria applanata and Physcia orientalis, and the air dose rate (μSv/h) at the sampling sites were investigated. (137)Cs in P. orientalis measured about 1 year after the Fukushima nuclear accident was correlated (r(2) = 0.80) more closely with the air dose rate than those measured after about 2 years (r(2) = 0.65), possibly demonstrating its continued value as a biomonitor to reflect ambient fall-out levels. In contrast, those of Dirinaria applanata were not correlated with the air dose rate in either year.

(137)Cs concentrations in ten species of foliose lichens collected within Tsukuba-city in August 2013 ranged from 1.7 to 35 kBq/kg. The relationships between (137)Cs in two dominant species, Dirinaria applanata and Physcia orientalis, and the air dose rate (μSv/h) at the sampling sites were investigated. (137)Cs in P. orientalis measured about 1 year after the Fukushima nuclear accident was correlated (r(2) = 0.80) more closely with the air dose rate than those measured after about 2 years (r(2) = 0.65), possibly demonstrating its continued value as a biomonitor to reflect ambient fall-out levels. In contrast, those of Dirinaria applanata were not correlated with the air dose rate in either year.