Search

Many fungi live as mycelia, which are networks of hyphae. Mycelial networks are suited for the widespread distribution of nutrients and water. The logistical capabilities are critical for the extension of fungal survival areas, nutrient cycling in ecosystems, mycorrhizal symbioses, and virulence. In addition, signal transduction in mycelial networks is predicted to be vital for mycelial function and robustness. A lot of cell biological studies have elucidated protein and membrane trafficking and signal transduction in fungal hyphae; however, there are no reports visualizing signal transduction in mycelia. This paper, by using the fluorescent Ca2+ biosensor, visualized for the first time how calcium signaling is conducted inside the mycelial network in response to localized stimuli in the model fungus Aspergillus nidulans. The wavy propagation of the calcium signal inside the mycelium or the signal blinking in the hyphae varies depending on the type of stress and proximity to the stress. The signals, however, only extended around 1,500 μm, suggesting that the mycelium has a localized response. The mycelium showed growth delay only in the stressed areas. Local stress caused arrest and resumption of mycelial growth through reorganization of the actin cytoskeleton and membrane trafficking. To elucidate the downstream of calcium signaling, calmodulin, and calmodulin-dependent protein kinases, the principal intracellular Ca2+ receptors were immunoprecipitated and their downstream targets were identified by mass spectrometry analyses. Our data provide evidence that the mycelial network, which lacks a brain or nervous system, exhibits decentralized response through locally activated calcium signaling in response to local stress.

Myco-talpology is the science of mushrooms and talpid moles based on our discovery in 1976 that underground mole nests can be located by the aboveground fruiting of the agaricsHebeloma danicumorHebeloma sagarae, a Japanese sibling species of EuropeanHebeloma radicosum. Hyphae of these mushrooms specifically colonise mole latrines near nests, forming ectomycorrhizas with the roots of their host trees. By this process, the hyphae and roots absorb, transform, and translocate the nutrients from mole excretions, cleaning the mole’s habitat. The mushrooms fruit on the ground with thick root-like tissue stretching up from the ectomycorrhizas. The presence of the fruit bodies serves as the only indicator for underground mole nests, enabling us to provide novel insights into mole ecology. We excavated 74H. sagaraeorH. danicumsites in Japan and 13H. radicosumsites in Europe and identified the nesting species. These investigations provided new perspectives on latrine making, nest structure, breeding and nestlings, the neighbouring presence of different Talpini species, and long-term nesting at the same site with inhabitant changes. Moreover, they suggested that a tripartite habitat-cleaning symbiosis among moles, mushrooms, and mushroom-host trees in the latrine must have existed for a long time in Japanese and European forests. While moles are traditionally considered inhabitants of open areas, their special relationship with mushrooms and trees suggests they may originally be forest inhabitants.

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.

Hondo spruce (Picea jezoensis var. hondoensis (Mayr) Rehder)) is separately distributed among several mountainous regions in central Japan as remnant populations of the last glacial period. To identify factors that affect Hondo spruce seedling regeneration on decaying logs, we investigated the relationships between climatic conditions, log properties, including decay type by fungi, and Hondo spruce seedling density on logs using data from seven subalpine Hondo spruce forests in central Japan. The results showed that the presence of soft rot was associated with higher seedling density, and the effect of brown rot in sapwood and white rot in heartwood on the predicted number of spruce seedlings on logs switched from positive to negative with increasing temperature and precipitation. Because soft rot occurs under humid conditions, the use of forest management techniques that increase the number of logs with soft rot in sapwood (e.g., by keeping the forest floor moist) are recommended for the sustainable regeneration of Hondo spruce. However, the relationships between wood decay type and seedling regeneration can also be affected by climate condition and thus are more complex than previously thought.

Saprotrophic cord-forming basidiomycetes, with their mycelial networks at the soil/litter interface on the forest floor, play a major role in wood decomposition and nutrient cycling/relocation. Many studies have investigated foraging behaviour of their mycelium, but there is little information on their intelligence. Here, we investigate the effects of relative size of inoculum wood and new wood resource (bait) on the decision of a mycelium to remain in, or migrate from, inoculum to bait using Phanerochaete velutina as a model. Experiments allowed mycelium to grow from an inoculum across the surface of a soil microcosm where it encountered a new wood bait. After colonisation of the bait, the original inoculum was moved to a tray of fresh soil to determine whether the fungus was still able to grow out. This also allowed us to test the mycelium’s memory of growth direction. When inocula were transferred to new soil, there was regrowth from 67% of the inocula, and a threshold bait size acted as a cue for the mycelium’s decision to migrate for a final time, rather than a threshold of relative size of inoculum: bait. There was greater regrowth from the side that originally faced the new bait, implying memory of growth direction.

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.

Dead wood is an important habitat for both fungi and insects, two enormously diverse groups that contribute to forest biodiversity. Unlike the myriad of studies on fungus–insect relationships, insect communities on ascomycete sporocarps are less explored, particularly for those in hidden habitats such as underneath bark. Here, I present my observations of insect community dynamics on Biscogniauxia spp. on oak dead wood from the early anamorphic stage to matured teleomorph stage, aided by the debarking behaviour of squirrels probably targeting on these fungi. In total, 38 insect taxa were observed on Biscogniauxia spp. from March to November. The community composition was significantly correlated with the presence/absence of Biscogniauxia spp. Additionally, Librodor (Glischrochilus) ipsoides, Laemophloeus submonilis, and Neuroctenus castaneus were frequently recorded and closely associated with Biscogniauxia spp. along its change from anamorph to teleomorph. L. submonilis was positively associated with both the anamorph and teleomorph stages. L. ipsoides and N. castaneus were positively associated with only the teleomorph but not with the anamorph stage. N. castaneus reproduced and was found on Biscogniauxia spp. from June to November. These results suggest that sporocarps of Biscogniauxia spp. are important to these insect taxa, depending on their developmental stage.

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.

Dead wood is an important microsite for seedling regeneration in forest ecosystems. Although recent studies have found important associations between fungal wood decay type (white rot and brown rot) and both density and species composition of regenerating seedlings, its abiotic and biotic mechanisms are unknown. In the present study, pot experiments were conducted with the seedlings of two ectomycorrhizal tree species (Abies veitchii and Betula ermanii) and two arbuscular mycorrhizal tree species (Chamaecyparis obtusa and Cryptomeria japonica) to evaluate their growth using three substrates: brown rot wood, white rot wood, and soil. Results showed that the shoot growth of B. ermanii grown in white rot wood was greater than in other substrates, but this effect disappeared in sterilized substrates, suggesting some biotic positive effects occur in white rot wood. The seedling weights of Cr. japonica and Ch. obtusa were found to be greater in soil than in wood, and this may be partly attributable to the high mycorrhizal rate of their roots in soil. Colonization of arbuscular and ectomycorrhizal fungi was restricted to the seedlings in unsterilized soil. These results demonstrate the importance of the biological mechanisms affecting seedlings’ preferences for a variety of regeneration microsites and illustrate the need for future experiments to include larger sets of seedling species.

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.

There is little available data on the biogeography of myxomycetes at the regional scale within any given climate zone. To investigate the geographical distribution of these protozoans, we focused on corticolous myxomycetes associated with the bark of Cryptomeria japonica trees, which we sampled extensively throughout Japan. Myxomycete sporophores developed in 73% of 2244 moist-chamber cultures of 188 bark samples from 24 regions, including 31 species. The most abundant species were Paradiacheopsis rigida and Cribraria confusa, which accounted for over 20% of all myxomycetes sampled. Non-metric multidimensional scaling was used to analyze the distribution of myxomycetes in relation to geographical variables and bark pH. The distribution of myxomycetes was influenced by altitude, temperature and bark pH. Temperature gradients and relative abundance of species were negatively correlated in P. rigida and Comatricha laxa and positively correlated in C. confusa, Macbrideora cornea, and Diderma chondrioderma. Bark pH was also positively correlated with the relative abundance of C. confusa, D. chondrioderma, and Physarum nutans and negatively correlated with that of P. rigida, P. cribrata, Enerthnema papillatum, and E. melanospermum. Geographical distribution of corticolous myxomycete communities was determined based on temperature and bark pH, which acted as local barriers in our study area.

Over the past few decades, rural forest ecosystems in Japan have experienced dynamic vegetation changes due to forest dieback and changes in land use, leading to the loss of local species populations and biodiversity. The aim of this study was to evaluate the importance of pine (Pinus densiflora) stumps and logs for tree seedling regeneration in a mixed natural forest in Kyoto Prefecture, Japan, that had previously experienced severe pine dieback, and to determine which factors most greatly affect seedling establishment. Seedlings of 17 tree species were recorded on pine stumps and logs in later stages of decay, among which Chamaecyparis obtusa and Rhododendron reticulatum were most dominant. Both of these species had a greater density on pine stumps than on logs or soil, despite stumps covering less than 0.5% of the study area. In addition, the seedling densities of both species were positively associated with moss cover on coarse woody debris, but negatively associated with wood pH. Brown rot in the sapwood and heartwood, which occurred more frequently in stumps than in logs, also positively associated with the seedling densities of both species. Predictive modelling showed that C. obtusa seedlings exhibited a stronger response to pH in stumps than in logs. Therefore, since brown-rotted wood is acidic due to fungal decay activities, brown-rotted pine stumps may present hotspots of C. obtusa seedling regeneration at the study site.

Myxomycetes are one of the major microbial predator groups found in detrital food webs within terrestrial ecosystems. They are typical inhabitants of coarse woody debris (CWD). However, the association between fungal communities and the foraging habits of myxomycetes has not been explored sufficiently in the field. Our study aimed to find community relationships between myxomycetes and fungi, a potential prey, on CWD, and the trophic status of saproxylic myxomycetes using stable isotope analysis of their sporocarps. Records of sporocarps present on 184 Pinus densiflora logs during a 3-year period listed 37 species of myxomycetes and 45 species of fungi. Ordination analysis using occurrence data of 34 dominant species (17 myxomycetes and 17 fungi) revealed their dynamic succession during log decay. Fungal dominants were clearly divided into two groups—earlier and later— and the majority of myxomycetes occurred during the middle stages of log decay between the first and second groups of fungal dominants. Species level associations between fungal and myxomycetes communities were rare. Isotopic nitrogen (δ15N) values of myxomycetes were significantly higher than those of wood-decay fungi, but few myxomycetes showed δ15N values higher than those of ectomycorrhizal fungi. Isotopic carbon (δ13C) values of myxomycetes were not significantly different from those of fungi. δ15N values of myxomycetes and fungi and δ13C of myxomycetes significantly increased with an increase in wood decay. However, these positive correlations between stable isotope profiles and wood decay disappeared after the values were calibrated by subtracting the δ15N and δ13C values of sapwood from those of myxomycetes and fungi. While saproxylic myxomycetes have long been assumed to be bacterivous, the results of this study suggest that wood-decay fungi could be an important part of their diet, and their foraging associations might be non-species specific.

Hyphal growth rates were tested on malt extract agar plates at eight different temperatures (5–40 °C) using 36 isolates of 17 basidiomycete species obtained from Pinus densiflora deadwood in Japan. All isolates of four brown rot species showed optimum growth at 30 °C, whereas the optimum growth temperature of white rot species varied from 20 °C to 30 °C. Analysis using a dataset from four cooler sites showed that brown rot fungi grew more rapidly than white rot fungi at higher temperatures (25 °C, 30 °C, and 35 °C). These results suggest that the hyphal growth of brown rot fungi might be physiologically adapted to higher temperatures than those of white rot fungi among the fungal species inhabiting deadwood of P. densiflora in Japan.

Deadwood is an important habitat for bryophytes in boreal and subalpine forests. The type of decay in wood (white, brown, and soft rot) caused by fungal colonizers has been revealed to affect bryophyte communities. However, little is known about the effects of decay type on the growth of bryophytes. We tested the effect of wood decay type on gametophyte growth for two common bryophyte species, Scapania bolanderi Austin and Pleurozium schreberi (Brid.) Mitt., which dominate the logs in subalpine coniferous forest on Mt. Ontake, in central Honshu, Japan. We used pot culture experiments in an open-sky nursery field. After eight months of cultivation, the growth of S. bolanderi was larger on brown rot wood than white rot wood, but the growth of P. schreberi was not. Mixed cultures of the two species also showed greater growth on brown rot wood. However, growth of S. bolanderi was significantly smaller than P. schreberi in mixed culture. These results suggest that brown rot wood enhances growth of S. bolanderi...

Fungal decomposition of coarse woody debris has an essential role in the biodiversity and carbon and nutrient dynamics in forest ecosystems. However, our knowledge of the effects of fungal species and within-stem diversity on wood decay is limited. In this paper, I described the process of wood decay and fungal succession of pine (Pinus densiflora) snags using chronosequence method. The results showed that the decay process differed between sapwood and heartwood. Sapwood decayed faster than heartwood, despite their initial densities being the same. Sapwood decay occurred in two phases. The first phase involved a typical white-rot process wherein acid-unhydrolysable residue (lignin) and holocellulose decayed simultaneously. White-rot species, such as Trichaptum abietinum and Phanerochaete sordida, were the dominant fungi and were likely the functional decomposers in this phase. The second phase involved selective decomposition of holocellulose. The dominant fungi in this phase included soft-rot species, such as Trichoderma spp., that can decompose holocellulose in wood that was previously delignified by white-rot species. In contrast to sapwood, heartwood experienced less loss of wood density and no clear change in lignocellulose composition, even in later stages of decay. Dominant fungi in heartwood included the latent inhabitants of living pine trees, such as Ascocoryne cylichnium, which is known to reduce colonization and wood decay by strong decomposers. These results suggest that, in addition to decay-resistant chemicals present in heartwood, the differences in the fungal communities present in heartwood and sapwood were responsible for the differences in their decay rates.

Fungal communities associated with plant tissues were compared between two bryophyte species dominating decaying logs (Scapania bolanderi and Pleurozium schreberi), and roots of spruce seedlings growing on the bryophytes and in the ground soil, to evaluate the contribution of fungal communities to seedling regeneration. Using high-throughput DNA sequencing, a total of 1233 fungal operational taxonomic units (OTUs) were detected. Saprotrophic Ascomycota were dominant in bryophytes, whereas ectomycorrhizal (ECM) Basidiomycota were dominant in spruce roots. Fungal communities were significantly different between the two bryophyte species. In addition, fungal communities of spruce seedlings were significantly affected by the substrates on which they were growing. Some ECM fungi were detected from both of the bryophytes and the spruce seedlings growing on them; however, the dominant OTU identities differed between the two bryophyte systems. The possible effects of functional differences between dominant fungal OTUs on spruce seedling regeneration are discussed.

Although the importance of bryophyte colonies on tree seedling establishment on downed logs is widely known, the mechanisms of how various bryophyte species affect seedlings are poorly understood. In this study, we analyzed the relationships between bryophyte community (colony coverage and thickness of each species) and tree seedlings growing on logs along the decay process. In an old-growth subalpine coniferous forest dominated by spruce, juvenile seedling density of spruce on downed logs was positively associated with the coverage of a liverwort Scapania bolanderi and the thickness of the bryophyte colonies, but was negatively associated with the coverage of a moss Hylocomium splendens. Coverage of S. bolanderi was also associated with shoot length of spruce seedlings, but this effect was negative. Coverage of S. bolanderi increased with log decay and became the most dominant species in the penultimate stage of log decomposition, but was replaced by thicker H. splendens in the final decay stage. These results suggested that S. bolanderi colonies, dominant only in the mid-stage of log decomposition, may indicate a ‘window of time’ for spruce seedlings to colonize on logs in this old-growth subalpine coniferous forest. Thus, when trying to understand sustainable regeneration mechanisms in subalpine forests, this interaction should be considered.

Evaluating the environmental factors that affect seedling regeneration on deadwood is important for predicting the forest recovery process after dieback events. Pine wilt disease (PWD) has killed many adult trees of Pinus densiflora in recent decades and consequently created a huge accumulation of deadwood in lowland forests in Japan. These deadwoods are now providing nice seedbeds for variety of tree species including Cryptomeria japonica, which is the most important timber species in Japan. In the present study, we tested the effects of various factors on Cryptomeria seedlings growing on decayed Pinus logs in Japan. In total, 126 individuals of Cryptomeria seedlings (height

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.

Decomposition subsystems have an essential role in forest dynamics but few studies demonstrate the effect of microbial decay traits on seedling regeneration. In the present study, we focused on seedling regeneration on coarse woody material (CWM), which is an important regeneration site for forest tree species, and the effects of wood decay type according to fungal decay preference for wood structural components on seedling colonization. Effects of log properties including wood decay type and other environmental variables on seedling density were evaluated by ordination methods and generalized linear models. In total, 22 woody species were recorded as seedlings on Pinus densiflora logs. By ordination analysis, white rot in heartwood and brown rot in sapwood, as well as canopy openness and log diameter, showed significant association with seedling communities. The factors selected for a generalized linear model for explaining seedling densities of the two dominant seedling species Cryptomeria japonica and P. densiflora included brown rot in sapwood and white rot in heartwood, but the effects were different: a positive effect of brown rot on C. japonica and a negative effect of white rot on P. densiflora. These results suggested that wood decay type could induce niche separation between dominant tree species regenerating on CWM.

There is growing evidence demonstrating the diversity of foliar endophytic fungi and their ecological roles in the survival of tree seedlings. However, the factors that shape fungal communities in tree seedlings within natural forest ecosystems remain poorly understood. Here, we evaluated the composition of foliar endophytic fungi growing in current-year seedlings of Cornus controversa and Prunus grayana in a cool temperate deciduous forest through a seed-sowing experiment and fungal isolation. The composition of endophytic fungi was affected by canopy tree species, canopy openness, and time after germination. In total, 27 and 22 fungal taxa were isolated from C. controversa and P. grayana seedlings, respectively. The dominant fungal taxa in both seedling species were Colletotorichum spp., and their isolation frequencies were higher under C. controversa canopies than under P. grayana canopies; the frequencies also increased with time after germination. These results suggest that overstory tree species strongly influences the endophytic fungal communities of understory seedlings.

Decaying logs are important seedbeds in boreal and subalpine forests. However, biotic and abiotic factors and their interactions related to seedling colonization patterns on logs remain unclear. In the present study, we evaluated the influence of bryophyte communities, wood decay type (white-, brown-, and soft-rot) owing to decomposer fungal activities, and environmental abiotic factors on seedling establishment in an old-growth subalpine coniferous forest in Japan. Among the tree species recorded on the conifer logs, Picea jezoensis var. hondoensis was the most dominant. Log surfaces were covered with distinctive patches of liverwort Scapania bolanderi and moss Pleurozium schreberi (approximately 33% cover for each). Redundancy analysis showed that brown-rot in sapwood significantly affects the bryophyte and seedling community on the logs. Generalized linear models suggested that the total bryophyte cover, Scapania cover, and white-rot in heartwood positively associate with Picea seedling density, whereas Pleurozium cover and basal area of adjacent Picea adults negatively associate with Picea seedling density. Results of structural equation modeling suggested that the brown-rot of sapwood positively associates with Scapania cover that has a positive effect on Picea seedling density. Furthermore, brown-rot of sapwood inhibited the Pleurozium cover, thus contributing to the Scapania dominance on the logs. These results suggest that fungal wood decomposer activities affect colonization of Picea seedlings in an indirect way via structuring bryophyte community on the logs.

Coarse woody debris (CWD) forms an important habitat suitable for tree seedling establishment, and the CWD decay process influences tree seedling community. In Japan, a severe dieback of Pinus densiflora Sieb. & Zucc. caused by pine wilt disease (PWD) damaged huge areas of pine stands but creates huge mass of pine CWD. It is important to know the factors influencing seedling colonization on pine CWD and their variations among geographical gradient in Japan to expect forest regeneration in post-PWD stands. I conducted field surveys on the effects of latitude, climates, light condition, decay type of pine logs, and log diameter on tree seedling colonization at ten geographically distinct sites in Japan. In total, 59 tree taxa were recorded as seedlings on pine logs. Among them, 13 species were recorded from more than five sites as adult trees or seedlings and were used for the analyses. A generalized linear model showed that seedling colonization of Pinus densiflora was negatively associated with brown rot in sapwood, while that of Rhus trichocarpa was positively associated with brown rot in heartwood. Regeneration of Ilex macropoda had no relationships with wood decay type but negatively associated with latitude and MAT, while positively with log diameter. These results suggested that wood decay type is a strong determinant of seedling establishment for certain tree species, even at a wide geographical scale; however, the effect is tree species specific.

Summary 1.In forest communities, the Janzen–Connell (J-C) hypothesis proposes that species diversity is maintained by non-competitive distance- and/or density-dependent seedling mortality caused by host-specific natural enemies. However, the effects of pathogen associations from nearby conspecifics vs. heterospecifics remain unknown in spatially heterogeneous light environments. 2.Seeds of hardwood species Cornus controversa (Cornus) and Prunus grayana (Prunus) were sown beneath 6–7 Cornus and Prunus adults in both the forest understory (FU) and in gaps (Gap) created by felling all woody vegetation near the focal adults. Seedling growth, mortality, killing agents (e.g. pathogens that cause damping-off and leaf diseases), and root infection by arbuscular mycorrhizal fungi (AMF) were investigated. 3.We found strong habitat effects on the expression of soil fungi beneath both tree species. Seedling mortality caused by soil-borne damping-off pathogens was greater in FU than in Gap, and AMF infection, which enhanced relative seedling growth rate, was greater in Gap than in FU. Seedling mortality caused by damping-off pathogens did not differ between Cornus and Prunus seedlings beneath the adults of conspecific or heterospecific adults in both FU and Gap, suggesting little distance-dependence or host preference in the fungus. 4.Beneath the adults of Cornus and Prunus, the most prevalent leaf diseases were zonate leaf blight and angular leaf spot caused by the airborne pathogenic fungi Haradamyces foliicola and Phaeoisariopsis pruni-grayanae, respectively. Although these pathogens attacked the seedlings of both species, conspecific seedlings (i.e. home) showed more severe leaf damage, earlier leaf shedding and/or less defensive behaviour (cell wall defence) relative to heterospecific seedlings (i.e. away), suggesting negative distance-dependent attack (i.e. host preference) for these leaf diseases. As a result, greater seedling mortality was observed for conspecific seedlings under both FU and Gap treatments. 5.Synthesis. In the temperate forest, the J-C hypothesis is largely mediated through the strong negative influence of airborne leaf diseases rather than through soil-borne damping-off pathogens. We found that airborne diseases demonstrated distance-dependent host preferences, which led to greater conspecific seedling damage regardless of environmental light conditions. This article is protected by copyright. All rights reserved.

To assess the nutrient mobilization ability of myxomycete plasmodia in deadwood, a microcosm experiment was conducted. Alive or dead plasmodia of a common lignicolous myxomycete, Physarum rigidum , were inoculated on field-collected crushed wood powder of white-rot or brown-rot pine wood and incubated for 24 d. The activity of living plasmodia led to increased concentrations of Ca 2+ , K + , Mg 2+ , Na + , and Cl − , but lower PO 4 3– concentrations in the wood powder. For NO 3 − concentration, the effect of living plasmodia was negative in white-rotted wood but positive in brown-rotted wood. These results suggest that the plasmodium of P. rigidum has the ability to mobilize nutrients in deadwood.

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.

Theory predicts that the energetic cost of competition between fungal mycelia might accelerate or retard the rate of wood decomposition, depending on various factors. To evaluate the effect of occupied territory on wood decay rate and competitive outcome, we set up a pairing competition experiment using beech wood blocks colonised by three brown-rot and three white-rot basidiomycetes. All white-brown combinations (totalling nine), and five ratios of wood volume (4:0, 3:1, 2:2, 1:3, 0:4) were performed. Pairings were incubated in the dark at 20 °C for 3 months, and then competition outcome and wood weight loss were determined. Mycelia occupying larger territory were more competitive than mycelia occupying smaller territory. There were negative relationships between wood volume and percentage wood weight loss. Wood decay was slower at the competition front than at the rear of the wood blocks in some cases. These results suggest that wood volume (territory size) affects both competition outcome and wood decay rate in basidiomycete communities.

Fungi are the main agents of coarse woody debris decomposition in forest ecosystems. We examined the associations of environmental variables with fungal community structures in dead pine logs at 12 geographically distant sites using amplicon pyrosequencing of fungal ITS rDNA. A total of 575 operational taxonomic units (OTUs) were identified based on clustering at 97% similarity. Among the known fungal ecological groups, saprotrophic fungi generally showed highest frequency of occurrence and were positively associated with mean annual temperature (MAT) and log diameter. Wood decay fungi with unknown decay type were positively associated with pine wilt disease and negatively associated with log diameter. Ordination analysis of the 42 most prevalent OTUs showed that MAT and annual precipitation significantly explained the observed fungal community structure. These results suggested that climate conditions and site history differentially effect structure fungal communities in pine logs among different ecological groups.

The decay process of coarse woody debris (CWD) is crucial for biodiversity in forest ecosystems. Wood decay types, traditionally categorized into white, brown, and soft rots, are the consequence of fungal decay activities and strongly structure the communities inhabiting CWD. It is important to evaluate the occurrence patterns of the decay types along a geographical range to understand forest biodiversity in wide scale. I examined the effects of environmental variables on the occurrence of wood decay types in pine logs in 30 sites covering a latitudinal gradient in Japan, including sites damaged by pine wilt disease (PWD) in recent decades. Among the wood decay types, the frequency of brown rot was negatively correlated with latitudinal gradient and that of soft rot was positively correlated with mean annual temperature (MAT), suggesting that lignin accumulation during pine log decomposition is more prominent in the warmer lower-latitude areas than in the cooler higher-latitude areas of Japan. In contrast, white rot was negatively correlated with MAT. The effects of precipitation, PWD, log diameter, soil contact, and bark and moss covers on decay type were also apparent. Number of different decay types within a log was negatively correlated with latitude and positively correlated with pesticide. The effects of current vegetation was not detected.

Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy was applied to coarse woody debris (CWD) in different stages of decomposition and collected from forest floor of a subtropical, a cool temperate, and a subalpine forest in Japan. The purpose was to test its applicability to characterize organic chemical composition of CWD of broad-leaved and coniferous trees from different climatic conditions. O-alkyl-C, mainly representing carbohydrates, was the predominant component of CWD at the three sites, accounting for 43.5-58.1% of the NMR spectra. Generally, the relative area under the signals for aromatic-C and phenolic-C, mainly representing lignin, increased, whereas the relative area for O-alkyl-C decreased, as the decay class advanced. The relative area under NMR chemical shift regions was significantly correlated with the chemical properties examined with proximate analyses. That is, O-alkyl-C and di-O-alkyl-C NMR signal areas were positively correlated with the volumetric density of CWD and the content of total carbohydrates. Methoxyl-C, aromatic-C, phenolic-C, carboxyl-C, and carbonyl-C were positively correlated with the contents of acid-unhydrolyzable residues (lignin, tannins, and cutin) and nitrogen. Lignin-C calculated from NMR signals increased, and polysaccharide-C decreased, with the decay class of CWD at the three study sites. A review of previous studies on 13C NMR spectroscopy for decomposing CWD suggested further needs of its application to broad-leaved trees from tropical and subtropical regions.

Dead wood is an important habitat for forest organisms, and wood decay fungi are the principal agents determining the dead wood properties that influence the communities of organisms inhabiting dead wood. In this study, we investigated the effects of wood decomposer fungi on the communities of myxomycetes and bryophytes inhabiting decayed logs. On 196 pine logs, 72 species of fungi, 34 species and seven varieties of myxomycetes, and 16 species of bryophytes were identified. Although white rot was the dominant decay type in sapwood and heartwood, brown and soft rots were also prevalent, particularly in sapwood. Moreover, white rot and soft rot were positively and brown rot negatively correlated with wood pH. Ordination analyses clearly showed a succession of cryptogam species during log decomposition and showed significant correlations of communities with the pH, water content, and decay type of wood. These analyses indicate that fungal wood decomposer activities strongly influence the cryptogam communities on dead wood.

The climbing orchid Erythrorchis altissima is the largest mycoheterotroph in the world. Although previous in vitro work suggests that E. altissima has a unique symbiosis with wood-decaying fungi, little is known about how this giant orchid meets its carbon and nutrient demands exclusively via mycorrhizal fungi. In this study, the mycorrhizal fungi of E. altissima were molecularly identified using root samples from 26 individuals. Furthermore, in vitro symbiotic germination with five fungi and stable isotope compositions in five E. altissima at one site were examined. In total, 37 fungal operational taxonomic units (OTUs) belonging to nine orders in Basidiomycota were identified from the orchid roots. Most of the fungal OTUs were wood-decaying fungi, but underground roots had ectomycorrhizal Russula. Two fungal isolates from mycorrhizal roots induced seed germination and subsequent seedling development in vitro. Measurement of carbon and nitrogen stable isotope abundances revealed that E. altissima is a full mycoheterotroph whose carbon originates mainly from wood-decaying fungi. All of the results show that E. altissima is associated with a wide range of wood- and soil-inhabiting fungi, the majority of which are wood-decaying taxa. This generalist association enables E. altissima to access a large carbon pool in woody debris and has been key to the evolution of such a large mycoheterotroph.