Metabolic Diversity of Xylariaceous Fungi Associated with Leaf Litter Decomposition.

Fungi in the family Xylariaceae are primary agents of leaf litter decomposition. However, the diversity of carbon source utilization by xylariaceous fungi and the relative effects on this from environmental and phylogenetic factors are largely unknown. This study assessed the metabolic diversity and redundancy of xylariaceous fungi, associated with leaf litter decomposition, by measuring their in vitro capacity to utilize multiple carbon sources. The work identified the relative influences of geographic and climatic sources, as well as the taxonomic and phylogenetic relatedness, of the fungi. Using Biolog EcoPlateTM, 43 isolates belonging to Nemania, Xylaria, Nodulisporium, Astrocystis, and Hypoxylon, isolated from Castanopsis sieboldii leaf litter at eight sites in Japan, were found to have the capacity to utilize a variety of carbohydrates, amino acids/amines, carboxylic acids, and polymers. The genera of xylariaceous fungi and their origins significantly affected their metabolic diversity and utilization of carbon sources. Variation partitioning demonstrated that dissimilarities in carbon utilization among fungal isolates were mostly attributable to site differences, especially climatic factors: mean annual temperature and precipitation, and maximum snow depth. Moreover, xylariaceous isolates that originated from adjacent sites tended to have similar patterns of carbon source utilization, suggesting metabolic acclimation to local environmental conditions.

Functionally explicit partitioning of plant ß-diversity reveal soil fungal assembly in the subarctic tundra.

Metabarcoding technologies for soil fungal DNA pools have enabled to capture the diversity of fungal community and the agreement of their ß-diversity with plant ß-diversity. However, processes underlying the synchrony of the aboveground-belowground biodiversity is still unclear. By using partitioning methods for plant ß-diversity, this study explored the process driving synchrony in tundra ecosystems, in which drastic vegetation shifts are observed with climate warming. Our methods based on Baselga's partitioning enabled the division of plant ß-diversity into two phenomena and three functional components. Correlation of fungal ß-diversity with the components of plant ß-diversity showed that the spatial replacement of fungi was promoted by plant species turnover, in particular, plant species turnover with functional exchange. In addition, spatial variety of graminoid or forbs species, rather than shrubs, enhanced fungal ß-diversity. These results suggest the importance of small-scale factors such as plant-fungal interactions or local environments modified by plants for the fungal community assemblage. The process-based understanding of community dynamics of plants and fungi allows us to predict the ongoing shrub encroachment in the Arctic region, which could weaken the aboveground-belowground synchrony.

Variability of decomposing ability among fungi associated with the bleaching of subtropical leaf litter.

A diverse array of fungi take part in decomposition, but the variability of their decomposing ability is not fully understood. A total of 49 isolates of Ascomycota and Basidiomycota were obtained from bleached areas of leaf litter in a subtropical forest in southern Japan, and their ability to decompose leaves and recalcitrant compounds was quantified in pure culture. Mass loss of leaves of Castanopsis sieboldii (Fagaceae) and Schima wallichii (Theaceae) was evaluated at 20 C for 12 wk in vitro. Fungi caused a loss of -0.4% to 34.3% of the original leaf mass. The greatest mass loss was caused by four isolates of Mycena (Tricholomataceae). Isolates of Lachnocladiaceae caused greater mass loss of recalcitrant compounds, registered as acid-unhydrolyzable residue (AUR), which includes lignin, relative to Xylariaceae. Isolates of Rhytismataceae, Lachnocladiaceae, Marasmiaceae, and Omphalotaceae exhibited selective decomposition of AUR, Mycena exhibited simultaneous decomposition of AUR and components other than AUR, and Xylariaceae exhibited selective decomposition of components other than AUR. Mass losses of leaves and AUR caused by each fungal isolate were similar for C. sieboldii and S. wallichii. The Mycena isolates obtained from C. sieboldii caused greater mass losses of leaves and AUR than those obtained from the other tree species, suggesting a "home-field advantage" of decomposing potentialities, with implications for natural interactions beyond the in vitro system evaluated here.

Bleaching of leaf litter accelerates the decomposition of recalcitrant components and mobilization of nitrogen in a subtropical forest.

Selective removal of lignin and other recalcitrant compounds, collectively registered as acid-unhyrolyzable residue (AUR), results in bleaching of leaf litter, but the importance of bleaching in decomposition processes on forest soil has not been fully evaluated. The aims of this study were to elucidate the occurrence of bleached area in decomposing leaf litter and to compare chemical composition between bleached and nonbleached portions in a subtropical forest in Japan. Field incubation of leaf litter was performed over an 18-month period with the litterbag method. The decomposition processes during the first 9 month were characterized by the relatively rapid mass loss and increase of bleached area, whereas the mass loss was slowed down and the bleached area decreased thereafter. Mass loss of leaf tissues was faster and AUR content was lower in bleached than in nonbleached portions, indicating the acceleration of mass loss in bleached leaf tissues by the selective decomposition of recalcitrant compounds. The decrease in carbonyl-C in the bleached portions was associated with the increase of extractable nitrogen. The results suggest that the bleaching plays a dominant role in the transformation and turnover of organic compounds and nitrogen in decomposing leaf litter.

Diversity and Geographic Distribution of Ligninolytic Fungi Associated With Castanopsis sieboldii Leaf Litter in Japan.

The diversity and geographic pattern of ligninolytic fungi were investigated within the distribution range of an evergreen tree, Castanopsis sieboldii (Fagaceae), in Japan. Fungal isolates obtained from 18 sites in subtropical and temperate regions in Japan were classified into 50 operational taxonomic units in Ascomycota and Basidiomycota according to the base sequence of the rDNA internal transcribed spacer region. Ordination by nonmetric multidimensional scaling showed the separation of fungal compositions between the study sites which was significantly related to the latitude, longitude, and mean annual temperature (MAT) of the study sites. We applied variation partitioning to separate the magnitude of the climatic, spatial, and leaf property factors and found the roles of MAT and spatial factors in structuring fungal assemblages, suggesting the importance of both niche processes and such non-niche processes as priority effect and dispersal limitation. The bleached area on leaf litter was greater at sites with higher MAT and precipitation located at lower latitudes and at sites where some major ligninolytic fungi occurred at greater relative frequencies, indicating that not only the climatic conditions but also the biogeographic patterns of distribution of ligninolytic fungi influence the decomposition of lignin in leaf litter.

Decomposition of Organic Chemical Components in Wood by Tropical Xylaria Species.

The ability of Xylaria species obtained from tropical wood and leaf litter to cause a mass loss of lignin and carbohydrates in wood was examined in vitro with pure culture decomposition tests. The mass loss of wood of four tree species caused by nine Xylaria isolates ranged from 4.5% to 28.4% of the original wood mass. These Xylaria isolates have a potential ability to decompose lignin and other recalcitrant compounds, collectively registered as acid unhydrolyzable residues or Klason lignin in wood. The origin of isolates (i.e., isolates from wood versus leaf litter) did not affect the mass loss of acid unhydrolyzable residue in wood. The Xylaria isolates tested generally caused a selective decomposition of polymer carbohydrates in wood in preference to acid unhydrolyzable residue. The mass loss of acid unhydrolyzable residue caused by Xylaria isolates varied with the tree species of the wood and was negatively related to the initial content of acid unhydrolyzable residue in wood, implying the limiting effect of lignin and recalcitrant compounds on wood decomposition by Xylaria isolates.

Two-years of investigation revealed the inconsistency of seasonal dynamics of an ectomycorrhizal fungal community in Japanese cool-temperate forest across years.

Ectomycorrhizal (ECM) fungal communities show temporal dynamics. Such dynamics have been mainly assessed with 1 year of investigations and have been related to the seasonal changes in environment. Recent study in sub-tropical region has revealed that stochastic temporal-based process can affect ECM fungal community, making the community of the same season different between years. The different community structures across years have also been observed in the Arctic region with a grass host. Nevertheless, in temperate zones, the effect of temporal-based processes and the consistency of seasonal dynamics have never been investigated. We conducted a 2-year root sampling in a cool temperate Fagus crenata forest to test whether the temporal variation of ECM fungal community composition could be explained by season. The explanation powers of temporal distance and environmental factors for the temporal dynamics of ECM fungal community were simultaneously evaluated. The variation in community structure was significantly explained by year but not by season, indicating that seasonal community structure differed between years. This difference in the community structure across years was partly explained by temporal factors. Our study implies that the temporal dynamics of ECM fungal communities in temperate forests are affected by temporal-based factors and can vary across years.

Evaluation of host effects on ectomycorrhizal fungal community compositions in a forested landscape in northern Japan.

Community compositions of ectomycorrhizal (ECM) fungi are similar within the same host taxa. However, careful interpretation is required to determine whether the combination of ECM fungi and plants is explained by the host preference for ECM fungi, or by the influence of neighbouring heterospecific hosts. In the present study, we aimed to evaluate the effects of host species on the ECM community compositions in a forested landscape (approx. 10 km) where monodominant forest stands of six ECM host species belonging to three families were patchily distributed. A total of 180 ECM operational taxonomic units (OTUs) were detected with DNA metabarcoding. Quantitative multivariate analyses revealed that the ECM community compositions were primarily structured by host species and families, regardless of the soil environments and spatial arrangements of the sampling plots. In addition, 38 ECM OTUs were only detected from particular host tree species. Furthermore, the neighbouring plots harboured similar fungal compositions, although the host species were different. The relative effect of the spatial factors on the ECM compositions was weaker than that of host species. Our results suggest that the host preference for ECM fungi is the primary determinant of ECM fungal compositions in the forested landscape.

Biogeographic Patterns of Ectomycorrhizal Fungal Communities Associated With Castanopsis sieboldii Across the Japanese Archipelago.

Biogeographic patterns in ectomycorrhizal (ECM) fungal communities and their drivers have been elucidated, including effects of host tree species and abiotic (climatic and edaphic) conditions. At these geographic scales, genotypic diversity and composition of single host tree species change with spatial and environmental gradients, reflecting their historical dispersal events. However, whether the host genotypes can be associated with the biogeographic patterns of ECM communities remains unclear. We investigated the biogeographic pattern of ECM fungal community associated with the single host species Castanopsis sieboldii (Fagaceae), whose genotypic diversity and composition across the Japanese archipelago has already been evaluated. ECM communities were investigated in 12 mature Castanopsis-dominated forests covering almost the entire distribution range of C. sieboldii, and we quantified the effect of host genotypes on the biogeographic pattern of ECM fungal communities. Richness and community composition of ECM fungi changed with latitude and longitude; these biogeographic changes of ECM community were significantly correlated with host genotypic variables. Quantitative analyses showed a higher relative explanatory power of climatic and spatial variables than that of host genotypic variables for the biogeographic patterns in the ECM community. Our results suggest historical events of host dispersal can affect the biogeographic patterns of the ECM fungal community, while their explanation power was lower than that for climatic filtering and/or fungal dispersal.

Light quality determines primary production in nutrient-poor small lakes.

The availability of nutrients for primary producers has long been thought to be the main limiting factor for primary productivity in nutrient-poor lake ecosystems. However, recent studies have indicated that the availability of light energy is also important. On the other hand, the amount of phototroph was reported to decrease in summer in Antarctic lakes, furthermore, the light environment underwater was shown containing high amount of ultraviolet energy in small Antarctic lakes. Here, we hypothesized that primary productivity is limited by not only nutrients and simple light quantity but also light quality in nutrient-poor lakes. Then, we investigate factors influencing primary production by benthic phototrophic communities in shallow nutrient-poor lakes. We examine the relationships between primary production in 17 Antarctic freshwater lakes and nutrient concentrations in lake and benthic water, temperature and light energy. Primary production is decreased by ultraviolet energy reaching the lake bed, showing that production is determined by light quality. We also correlate ultraviolet energy in lake water with the catchment area of each lake. Our results show that the underwater light environment has an important influence on primary production as a key limitation factor and is sensitive to materials in runoff from the surrounding environment for pristine lakes.

Temporal distance decay of similarity of ectomycorrhizal fungal community composition in a subtropical evergreen forest in Japan.

Community compositions of ectomycorrhizal (ECM) fungi are known to show spatial distance decay of similarity, which arises from both deterministic niche-based processes and stochastic spatial-based processes (e.g. dispersal limitation). Recent studies have highlighted the importance of incorporating the spatial-based processes in the study of community ecology of ECM fungi. However, few studies have investigated the temporal distance decay of similarity of ECM fungal communities. More specifically, the role of stochastic temporal-based processes, which could drive the temporal distance decay of similarity independently of niche-based processes, in the temporal variation of the communities remains unclear. Here we investigated ECM fungi associated with roots of Castanopsis sieboldii at 3-month intervals over a 2-year period. We found that dissimilarity of the ECM fungal community composition was significantly correlated with temporal distance but not with environmental distance among sampling dates. Both climatic and temporal variables significantly explained the temporal variation of the community composition. These results suggest that temporal variations of ECM fungi can be affected not only by niche-based processes but also by temporal-based processes. Our findings imply that priority effects may play important roles in the temporal turnover of ECM fungal community at the site.

Disentangling the relative importance of host tree community, abiotic environment and spatial factors on ectomycorrhizal fungal assemblages along an elevation gradient.

Recent studies have shown that changes in community compositions of ectomycorrhizal (ECM) fungi along elevation gradients are mainly affected by changes in host tree communities and/or in abiotic environments. However, few studies have taken the effects of processes related to fungal dispersal (i.e. spatial processes) into account and distinguished the effects of host community, abiotic environment and spatial processes on community composition along elevation gradients. This has left unclear the relative importance of these factors in structuring the ECM community assemblages. To address this, we investigated the community composition of ECM fungi along an elevation gradient in northern Japan with 454 meta-barcoding. We found that the community composition of ECM fungi changed along the elevation and that all three factors jointly affected the compositional changes. We separated the magnitude of importance of the three factors in structuring ECM fungal communities and found that most of the spatial variation in ECM fungal community was explained by host communities and abiotic environments. Our results suggest that while biotic and/or abiotic environments can be important factors in determining the ECM fungal community composition along an elevation gradient, spatial processes may also be a primary determinant.

Low multifunctional redundancy of soil fungal diversity at multiple scales.

Theory suggests that biodiversity might help sustain multiple ecosystem functions. To evaluate possible biodiversity-multifunctionality relationships in a natural setting, we considered different spatial scales of diversity metrics for soil fungi in the northern forests of Japan. We found that multifunctionality increased with increasing local species richness, suggesting a limited degree of multifunctional redundancy. This diversity-multifunctionality relationship was independent of the compositional uniqueness of each community. However, we still found the importance of community composition, because there was a positive correlation between community dissimilarity and multifunctional dissimilarity across the landscape. This result suggests that functional redundancy can further decrease when spatial variations in identities of both species and functions are simultaneously considered at larger spatial scales. We speculate that different scales of diversity could provide multiple levels of insurance against the loss of functioning if high-levels of local species diversity and compositional variation across locations are both maintained. Alternatively, making species assemblages depauperate may result in the loss of multifunctionality.

Bleaching of leaf litter and associated microfungi in subboreal and subalpine forests.

Fungal decomposition of lignin leads to the whitening, or bleaching, of leaf litter, especially in temperate and tropical forests, but less is known about such bleaching in forests of cooler regions, such as boreal and subalpine forests. The purposes of the present study were to examine the extent of bleached area on the surface of leaf litter and its variation with environmental conditions in subboreal and subalpine forests in Japan and to examine the microfungi associated with the bleaching of leaf litter by isolating fungi from the bleached portions of the litter. Bleached area accounted for 21.7%-32.7% and 2.0%-10.0% of total leaf area of Quercus crispula and Betula ermanii, respectively, in subboreal forests, and for 6.3% and 18.6% of total leaf area of B. ermanii and Picea jezoensis var. hondoensis, respectively, in a subalpine forest. In subboreal forests, elevation, C/N ratio and pH of the FH layer, and slope aspect were selected as predictor variables for the bleached leaf area. Leaf mass per area and lignin content were consistently lower in the bleached area than in the nonbleached area of the same leaves, indicating that the selective decomposition of acid unhydrolyzable residue (recalcitrant compounds such as lignin, tannins, and cutins) enhanced the mass loss of leaf tissues in the bleached portions. Isolates of a total of 11 fungal species (6 species of Ascomycota and 5 of Basidiomycota) exhibited leaf-litter-bleaching activity under pure culture conditions. Two fungal species (Coccomyces sp. and Mycena sp.) occurred in both subboreal and subalpine forests, which were separated from each other by approximately 1100 km.

Assessment of the fungal diversity and succession of ligninolytic endophytes in Camellia japonica leaves using clone library analysis.

Fungal assemblages in live, newly shed and partly decomposed leaves of Camellia japonica were investigated with a clone library analysis to assess the fungal diversity and succession in a subtropical forest in southern Japan. Partly decomposed leaves were divided into bleached and adjacent nonbleached portions to estimate the fungi functionally associated with lignin decomposition in the bleached portions, with an emphasis on Coccomyces sinensis (Rhytismataceae, Ascomycota). From 144 cloned 28S ribosomal DNA (rDNA) sequences, 48 operational taxonomic units (OTUs) were defined based on a sequence similarity threshold of 98%. Forty-one (85%) of the 48 OTUs belonged to the Ascomycota and seven OTUs (15%) to the Basidiomycota. Twenty-six OTUs (54%) were detected only once (singletons). The number of OTUs and the diversity indices of the fungal assemblages in the different leaves were in this order: live leaves > newly shed leaves > bleached portions > nonbleached portions of partly decomposed leaves. The fungal assemblages were similar in newly shed leaves and the bleached portions of partly decomposed leaves. Ligninolytic fungi of the genera Coccomyces, Lophodermium and Xylaria were frequently detected in the bleached portions. OTU3, identified as Coccomyces sinensis, was detected in live and newly shed leaves and the bleached portions of partly decomposed leaves, suggesting that this fungus latently infects live leaves, persists after leaf fall and takes part in lignin decomposition.

Endophytic fungi associated with leaves of Betulaceae in Japan.

Diversity and species composition of endophytic fungi on leaves of 11 tree species in Betulaceae were studied, with reference to climatic, tree species, and seasonal variations. A total of 186 fungal isolates were obtained from 190 leaves collected in a subalpine forest, a cool temperate forest, and a subtropical forest in Japan, and were divided into 46 operational taxonomic units (OTUs) according to the base sequences of D1-D2 region of large subunit rDNA. The 2 most frequent OTUs were Muscodor sp. and Nemania sp. in Xylariaceae, followed by Gnomonia sp., Glomerella acutata , Apiosporopsis sp., Asteroma sp., and Cladosporium cladosporioides . The similarities of OTU composition in endophytic fungal assemblages on leaves of Betulaceae were generally low among the forests of different climatic regions. Fungal OTU compositions were relatively similar between 2 Betula species in the subalpine forest, whereas 7 tree species in the cool temperate forest were divided into 3 groups according to the similarity of endophytic fungal assemblages on the leaves, with 4 Carpinus species assigned into 2 of the 3 groups. The similarity of endophytic fungal assemblages between August and October was relatively high in the subalpine forest, whereas the seasonal changes were generally greater (i.e., the similarities among sampling dates were lower) in the cool temperate forest.

Wood decomposing abilities of diverse lignicolous fungi on nondecayed and decayed beech wood.

We tested the decay abilities of 28 isolates from 28 lignicolous fungal species (Basidiomycota, Ascomycota and Zygomycota) with the pure culture test. We used beech wood powder in varying moisture conditions and decay stages (nondecayed, intermediately decayed and well decayed) as substrates. The weight loss in wood powder was -0.2-17.8%. Five isolates of Basidiomycota (Bjerkandera adusta, Mycena haematopus, Omphalotus guepiniformis, Trametes hirsuta, Trametes versicolor) caused high weight losses in nondecayed wood. We detected significant effects of decay stage on weight loss in wood in most isolates tested, whereas moisture content rarely had an effect on weight loss. Among Basidiomycota and Xylariaceae in Ascomycota weight loss was greater for nondecayed wood than for intermediately and well decayed wood. In contrast four isolates in Ascomycota (Scytalidium lignicola, Trichoderma hamatum, T. harzianum, T. koningii) caused substantial weight loss in intermediately and well decayed wood, although they rarely caused weight loss in nondecayed wood. Zygomycota caused low weight loss in wood. Wood decay stages also affected decomposition of wood chemical components. Acid-unhydrolyzable residue (AUR) decomposition was reduced, whereas holocellulose decomposition was stimulated by some strains of Basidiomycota and Ascomycota in well decayed wood. T. harzianum in particular caused significant weight loss of holocellulose in well decayed wood, although this fungus caused negligible weight loss of both AUR and holocellulose in nondecayed wood. We discuss these changes in the decay patterns of AUR and holocellulose with varying wood decay stages in relation to the role of fungal decomposition of woody debris in forests.

Altitudinal distribution of microfungi associated with Betula ermanii leaf litter on Mt. Rishiri, northern Japan.

The altitudinal distribution of microfungi associated with Betula ermanii Cham. leaf litter was investigated on Mt. Rishiri (1719 m), northern Japan. Fallen leaves were collected at five sites of different altitudes (approximately 300, 600, 900, 1200, and 1500 m above sea level) along a transect on the northern slope of Mt. Rishiri. A total of 35 species were isolated from Betula leaf litter of which 12 occurred frequently and were regarded as dominant microfungi. Species richness, diversity, and equitability of microfungal assemblages were lower at Site 1500 than at the other sites. Similarities in species composition were relatively high among Sites 300, 600, and 900, but similarities between these sites and sites at the higher altitudes (i.e., Sites 1200 and 1500) were relatively low. Similarity of species composition was relatively low between Sites 1200 and 1500. Cluster analysis showed that the 12 major microfungal species were classified into four groups according to their pattern of altitudinal distribution that peaked at Sites 600, 900, 1200, and 1500, respectively. These results suggest that the diversity and species composition of Betula microfungi are sensitive to environmental changes along the altitudinal transect on Mt. Rishiri, and this is especially so at the altitudes higher than approximately 1200 m. This implies that future environmental changes will have impacts on mountainous ecosystems through the changes in diversity and functional aspects of microfungal assemblages.

Endophytic and epiphytic phyllosphere fungi of Camellia japonica: seasonal and leaf age-dependent variations.

Seasonal and leaf age-dependent variations in the endophytic and epiphytic phyllosphere fungal assemblages of Camellia japonica were examined and compared. Live leaves of C. japonica were collected in four seasons (May, Aug, Nov, Feb), and fungi were isolated from healthy-looking leaves of 0, 1, 2 and 3 y old. The infection rate and total number of endophytic fungi increased May-Feb, and species richness of endophytes increased as leaves aged. In contrast the infection rate of epiphytic fungi was 100% for all leaf ages at every sampling date. The total number of epiphytic fungi isolated was greatest in May and lowest in Aug. The species richness of epiphytes did not differ significantly by season or leaf age. Eight fungal species were recorded as major phyllosphere fungi of C. japonica. Seasonal variations were detected for the frequencies of Colletotrichum gloeosporioides, C. acutatum, and epiphytes Pestalotiopsis sp.1, Aureobasidium pullulans, Phoma sp.1 and Ramichloridium sp., whereas the frequency of the endophyte Geniculosporium sp.1 varied with leaf age. The frequency of the epiphyte Cladosporium cladosporioides varied with both season and leaf age.

Colonization and decomposition of salal (Gaultheria shallon) leaf litter by saprobic fungi in successional forests on coastal British Columbia.

The colonization of leaf litter by saprobic fungi was studied in old-growth and post-harvest successional Douglas-fir forests on southeast Vancouver Island, British Columbia. This study focused on leaf litter of salal (Gaultheria shallon Pursh.), a dominant understory shrub in all stands. Salal litter is characterized by the occurrence of bleached portions attributable to fungal colonization of the litter and to the variable decomposition of recalcitrant compounds, such as lignin. Analyses of proximate chemical fractions, fungal assemblages on the bleached leaf area, and pure culture decomposition assays indicated that Marasmius sp. and Coccomyces sp. were responsible for rapid decomposition and bleaching of salal leaf litter. The bleached area accounted for 17%-22% of total area of salal leaf litter collected in immature (40-60 years old), mature (85-105 years old), and old-growth (more than 290 years old) stands, but for only 2% in regeneration (5-15 years old) stands. The reduction of bleached leaf area occupied by Marasmius sp. and Coccomyces sp. in regeneration stands could be due to the changes in microenvironmental conditions on the forest floor, in litter quality, or in food-web structure in soils. The decrease of fungi able to decay recalcitrant compounds may lead to a reduction of salal decomposition rates in clear-cut sites that would persist until canopy closure occurs.