Fungal decomposition of woody debris of Castanopsis sieboldii in a subtropical old-growth forest

Fungi, especially basidiomycetes, are the primary agents of woody debris decomposition in terrestrial forest ecosystems. However, quantitative data regarding the abundance and decay activity of wood-inhabiting fungi are lacking, especially for tropical and subtropical areas. This study demonstrates the dynamics of decay columns of wood-inhabiting fungi within decaying woody debris of Castanopsis sieboldii and the wood decay activities of those fungi in a subtropical natural forest. Among six basidiomycetes and two ascomycetes observed as sporocarps on fallen boles of C. sieboldii, Microporus affinis was most abundantly observed in terms of frequency of sporocarps and as percentage area of decay columns within cross-sections of boles, especially those in the early stages of decomposition. In decay columns of M. affinis, both acid-unhydrolyzable residue (AUR) and holocellulose decayed simultaneously, and wood relative density decreased to 45.8% of that of fresh C. sieboldii wood. A pure culture decay test under laboratory conditions showed that M. affinis was a strong decomposer of AUR and holocellulose. These results suggest that M. affinis has a central role in lignocellulose decomposition of wood of C. sieboldii in the early stages of decomposition.     

Small-scale variation in chemical property within logs of Japanese beech in relation to spatial distribution and decay ability of fungi

Fungal communities within a naturally fallen bough of Japanese beech (Fagus crenata) were investigated with reference to chemical properties of decay columns. Five logs were cut out from the fallen bough, which ranged from 10.7 to 20.5 cm in diameter. Nine fungal species and one sterile fungus were isolated from decay columns that elongated along a longitudinal axis and were delimited by black zone lines and wood discoloration. Lampteromyces japonicus and Trichoderma spp. were isolated from all five logs. Lampteromyces japonicus and Antrodiella albocinnamomea occupied the largest volume in the logs. Lignin and carbohydrate contents, lignocellulose index (LCI), nitrogen content, and water content were different among decay columns colonized by different fungal species in each log. In L. japonicus, LCI of decay column was correlated to that of wood blocks decayed under pure culture condition by the fungi isolated from the decay columns. These results suggest that the small-scale variation in chemical properties within fallen logs of Japanese beech reflects the distribution and the decay ability of colonized fungi.     

Fungal succession and decomposition of beech cupule litter

Beech cupule litter is the second largest (next to leaf litter) component of total annual litterfall in mast years, and makes an important contribution to carbon budgets in beech forest soils. We investigated the decomposition processes of beech cupule litter over a 30-month period with reference to the role of fungal succession in the decomposition of acid-unhydrolyzable residue (AUR) and holocellulose. During the study period, weight loss of holocellulose occurred, while there was little weight loss of AUR, and 77?% of the original cupule weight remained at the end of the study period. Xylaria sp.1, Geniculosporium sp. and Nigrospora sp. that can attack holocellulose selectively caused mass loss of holocellulose and were responsible for the cupule weight loss. Although the beech cupule is a woody phyllome and its lignocellulose composition is similar to that of coarse woody debris (CWD) rather than leaf litter of beech, the selective decomposition of holocellulose by fungi was similar to the decay process of leaf litter rather than CWD.     

Fungal succession and decomposition of <Emphasis Type="Italic">Camellia japonica</Emphasis> leaf litter

Decomposition processes of Camellia japonica leaf litter were investigated over an 18-month period with reference to the role of fungal succession in the decomposition of lignin and holocellulose. Decomposition and fungal succession were studied in bleached and nonbleached portions of litter, which were precolonized by ligninolytic and cellulolytic fungi, respectively. Coccomyces nipponicum and Lophodermium sp. (Rhytismataceae), which can attack lignin selectively, caused mass loss of lignin and were responsible for bleaching during the first 4 months (stage I), whereas cellulolytic fungi caused mass loss of holocellulose in adjacent nonbleached portions. Soluble carbohydrates and polyphenols also decreased rapidly during this stage. Pestalotiopsis guepini, coelomycete sp.1, and the Nigrospora state of Khuskia oryzae caused mass loss of holocellulose between 4 and 14 months (stage II) and Xylaria sp. caused mass loss of both lignin and holocellulose from 14–18 months (stage III). In stages II and III, decomposition was more rapid in bleached portions than in nonbleached portions probably due to the prior delignification of lignified holocellulose in bleached portions. Frequencies of these fungi showed different responses among species to the pattern of changes in lignin and holocellulose contents during decomposition. Total hyphal length increased in both portions over the study period, but mycelia of basidiomycetes accounted for about 2% of total hyphal length, suggesting that their role in fungal succession and decomposition was low. Lignin and nitrogen contents were consistently lower and holocellulose content was higher in bleached portions than in nonbleached portions during decomposition. The succession of ligninolytic and cellulolytic fungi was a major driving factor that promoted decomposition and precolonization by ligninolytic fungi enhanced decomposition.     

Decomposition of 14C-labeled cellulose substrates in litter and soil from a beechwood on limestone

The decomposition of three different ¹⁴C-labeled cellulose substrates (plant holocellulose, plant cellulose prepared from ¹⁴C-labeled beech wood (Fagus sylvatica) and bacterial cellulose produced by Acetobacter xylinum) in samples from the litter and mineral soil layer of a beechwood on limestone was studied. In a long-term (154 day) experiment, mineralization of cellulose materials, production of ¹⁴C-labeled water-soluble compounds, and incorporation of ¹⁴C in microbial biomass was in the order Acetobacter cellulose > holocellulose > plant cellulose in both litter and soil. In general, mineralization of cellulose, production of ¹⁴C-labeled water-soluble compounds, and incorporation of ¹⁴C in microbial biomass were more pronounced, but microbial biomass ¹⁴C declined more rapidly in litter than in soil. In short-term (14 day) incubations, mineralization of cellulose substrates generally corresponded with cellulase and xylanase activities in litter and soil. Pre-incubation with trace amounts of unlabeled holocellulose significantly increased the decomposition of ¹⁴C-labeled cellulose substrates and increased cellulase activity later in the experiment but did not affect xylanase activity. The sum of ¹⁴CO₂ production, ¹⁴C in microbial biomass, and ¹⁴C in water-soluble compounds is considered to be a sensitive parameter by which to measure cellulolytic activity in soil and litter samples in short-term incubations. Shorter periods than 14 days are preferable in assays using Acetobacter cellulose, because the decomposition of this substrate is more variable than that of holocellulose and plant cellulose.Offprint requests to: S. Scheu.     

Effects of Litter Inputs on N<Subscript>2</Subscript>O Emissions from a Tropical Rainforest in Southwest China

Litter inputs are expected to have a strong impact on soil N₂O efflux. This study aimed to assess the effects of the litter decomposition process and nutrient efflux from litter to soil on soil N₂O efflux in a tropical rainforest. A paired study with a control (L) treatment and a litter-removed (NL) treatment was followed for 2 years, continuously monitoring the effects of these treatments on soil N₂O efflux, fresh litter input, decomposed litter carbon (LCI) and nitrogen (LNI), soil nitrate (NO₃ ^?–N), ammonium (NH₄ ⁺–N), dissolved organic carbon (DOC), and dissolved nitrogen (DN). Soil N₂O flux was 0.48 and 0.32 kg N₂O–N ha^?1 year^?1 for the L and NL treatments, respectively. Removing the litter caused a decrease in the annual soil N₂O emission by 33%. The flux values from the litter layer were higher in the rainy season as compared to the dry season (2.10 ± 0.28 vs. 1.44 ± 0.35 μg N m^?2 h^?1). The N₂O fluxes were significantly correlated with the soil NO₃ ^?–N contents (P < 0.05), indicating that the N₂O emission was derived mainly from denitrification as well as other NO₃ ^? reduction processes. Suitable soil temperature and moisture sustained by rainfall were jointly attributed to the higher soil N₂O fluxes of both treatments in the rainy season. The N₂O fluxes from the L were mainly regulated by LCI, whereas those from the NL were dominated jointly by soil NO₃ ^? content and temperature. The effects of LCI and LNI on the soil N₂O fluxes were the greatest in the 2 months after litter decomposition. Our results show that litter may affect not only the variability in the quantity of N₂O emitted, but also the mechanisms that govern N₂O production. However, further studies are still required to elucidate the impacting mechanisms of litter decomposition on N₂O emission from tropical forests.     

Organic chemical and nutrient dynamics in decomposing beech leaf litter in relation to fungal ingrowth and succession during 3-year decomposition processes in a cool temperate deciduous forest in Japan

Decomposition processes of beech leaf litter were studied over a 3-year period in a cool temperate deciduous forest in Japan. Organic chemical and nutrient dynamics, fungal biomass and succession were followed on upper (Moder) and lower (Mull) of a forest slope. Litter decomposition rates were similar between the sites. Nutrient dynamics of the decomposing litter was categorized into two types: weight changes in nitrogen and phosphorus showed two phases, the immobilization (0–21 months) and the mobilization phase (21–35 months), while those in potassium, calcium and magnesium showed only the mobilization phase. The rate of loss of organic chemical constituents was lignin < holocellulose < soluble carbohydrate < polyphenol in order. The changes in lignocellulose index (LCI), the ratio of holocellulose in lignin and holocellulose, were significantly correlated to the changes in nitrogen and phosphorus concentrations during the decomposition. During the immobilization phase, increase in total fungal biomass contributed to the immobilization of nitrogen and phosphorus. The percentage of clamp-bearing fungal biomass (biomass of the Basidiomycota) to total fungal biomass increased as the decomposition proceeded and was significantly correlated to LCI. Two species in the xylariaceous Ascomycota were dominantly isolated by the surface sterilization method from decomposing litter collected in the 11th month. The organic chemical, nitrogen and phosphorus dynamics during the decomposition were suggested to be related to the ingrowth, substrate utilization and succession of the Xylariaceae and the Basidiomycota. Twenty-one species in the other Ascomycota and the Zygomycota isolated by the washing method were classified into three groups based on their occurrence patterns: primary saprophytes, litter inhabitants and secondary sugar fungi. These species showed different responses to LCI and soluble carbohydrate concentration of the litter between the groups.     

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.     

Accumulation and decay dynamics of coarse woody debris in a Japanese old-growth subalpine coniferous forest

Far less is known about the coarse woody debris (CWD) stock and decay process in temperate Asia compared with that in boreal and temperate Europe and North America. We estimated coniferous CWD stock (logs and snags), decay rate and process, and fungal species responsible for the decay process in a Japanese subalpine coniferous forest. The CWD mass was 42.4 Mg ha^?1, which was the greatest among the previous data recorded in temperate Asia. The decay rate calculated using the annual input of CWD divided by CWD accumulation was 0.036 year^?1, whereas the decay rate when measured chronosequentially was 0.020–0.023 year^?1. The decay process was divided into two phases characterized by different dominant organic chemical constituents. In the first phase, both acid-unhydrolyzable residue and holocellulose decayed simultaneously, suggestive of the white-rot process. In the second phase, holocellulose was selectively decomposed and AUR accumulated, suggestive of the brown-rot process. Nutrients (N, P, K, Na, Mg, and Ca) were mineralized in the first phase but immobilized in the second phase. The fruiting bodies of 26 taxa of fungi were recorded as occurring on CWD in the study area. Trichaptum abietinum and T. fuscoviolaceum, which dominated in the first phase and are known as white-rot fungi, were assumed to be the main decomposers of lignocellulose in the first phase. Although no known strong wood decomposers dominated the second phase, Laetiporus sulphureus and Oligoporus caesius, known as brown-rot fungi, were expected to participate in the selective decomposition of holocellulose in the second phase.     

Decomposition of Japanese beech wood by diverse fungi isolated from a cool temperate deciduous forest

We assessed 62 fungal strains in 31 species of wood decay fungi in the ability to decompose wood blocks of Japanese beech (Fagus crenata) under a pure culture condition. Fungi were collected in a cool temperate beech forest in Japan and isolated from the inside of beech logs and from sporocarps fruiting on logs and snags of beech that were different in diameter and decay class. Fungi in Holobasidiomycetidae showed marked decomposition of lignin and carbohydrate. These fungi were divided into three groups according to the pattern of lignin and carbohydrate utilization. Phanerochaete filamentosa decomposed lignin selectively. Lampteromyces japonicus, Steccherinum rhois, Trichaptum biforme, Stereum ostrea, Mycena haematopoda, Antrodiella albocinnamomea, Daedalea dickinsii, Daedaleopsis tricolor, Ganoderma tsunodae, and Trametes versicolor decomposed lignin and carbohydrates simultaneously. Psathyrella candolleana, Lenzites betulinus, and Trametes hirsuta decomposed carbohydrates selectively. Species in the Phragmobasidiomycetidae and in the Ascomycota caused low mass loss of wood.     

Limit values for decomposition and convergence process of lignocellulose fraction in decomposing leaf litter of 14 tree species in a cool temperate forest

We examined limit values for decomposition and lignocellulose index (LCI, the ratio of acid-soluble holocellulose to acid-soluble holocellulose plus acid-insoluble lignin and lignin-like substances) in leaf litter decomposition of 14 tree species over 3 years. The study was carried out on upper (moder) and lower parts (mull) of a forest slope that showed different humus accumulation forms in a cool temperate forest in Japan. Limit values for accumulated mass loss of litter ranged from 46.8% to 94.1% and were not different between the sites. Limit values were positively correlated to initial LCI and lignin content. Final values of LCI of 14 litter types at the end of the study period showed a convergent trend among litter types at 0.25–0.26 as compared to their initial values (0.41 mean). The final LCI was not different between the sites. A review of limit values and initial and final values of LCI in leaf litter of temperate and boreal forests indicated that the limit values and final LCI in litter types in Japan were lower than those in Europe and North America, which can be primarily ascribed to lower initial LCI in Japan.     

Type studies of <Emphasis Type="Italic">Pleurotus</Emphasis> reported from Japan

Eight type specimens of Pleurotus reported from Japan were examined. Four new combinations, Marasmius alopecius, Omphalotus guepiniformis, Marasmiellus leiophyllus, and Hohenbuehelia squamula, are proposed. Pleurotus cyatheae is accepted in the original genus. The following species are synonyms: Pleurotus harmandii, a synonym of Omphalotus guepiniformis; P. minutoniger, a synonym of Resupinatus striatulus; and P. pulchellus, a synonym of Hohenbuehelia tremula. Omphalotus japonicus (= Lampteromyces japonicus) is a synonum of O. guepiniformis.     

Succession of microfungi in Phillyrea angustifolia litter in a Mediterranean maquis in Sardinia

ABSTRACT

The colonisation of microfungi in litter bags with Phillyrea angustifolia L. leaf litter was followed for two years; the succession of microfungal communities was analysed. Two main groups of fungi were identified, whose presence is correlated with the successive decomposition stages of the substrate and with seasonal variations.     

Decomposition of <Superscript>15</Superscript>N-labelled beech litter and fate of nitrogen derived from litter in a beech forest

The decomposition and the fate of ¹⁵N- labelled beech litter was monitored in a beech forest (Vosges mountains, France) over 3 years. Circular plots around beech trees were isolated from neighbouring tree roots by soil trenching. After removal of the litter layer, ¹⁵N-labelled litter was distributed on the soil. Samples [labelled litter, soil (0–15 cm depths], fine roots, mycorrhizal root tips, leaves) were collected during the subsequent vegetation periods and analysed for total N and ¹⁵N concentration. Mass loss of the ¹⁵N-labelled litter was estimated using mass loss data from a litterbag experiment set up at the field site. An initial and rapid release of soluble N from the decomposing litter was balanced by the incorporation of exogenous N into the litter. Fungal N accounted for approximately 35% of the N incorporation. Over 2 years, litter N was continuously released and rates of N and mass loss were equivalent, while litter N was preferentially lost during the 3rd year. Released ¹⁵N accumulated essentially at the soil surface. ¹⁵N from the decomposing litter was rapidly (i.e. in 6 months) detected in roots and beech leaves and its level increased regularly and linearly over the course of the labelling experiment. After 3 years, about 2% of the original litter N had accumulated in the trees. ¹⁵N budgets indicated that soluble N was the main source for soil microbial biomass. Nitrogen accumulated in storage compounds was the main source of leaf N, while soil organic N was the main source of mycorrhizal N. Use of ¹⁵N-labelled beech litter as decomposing substrate allowed assessment of the fate of litter N in the soil and tree N pools in a beech forest on different time scales. Received: 3 May 1999 / Accepted: 3 January 2000     

Modeling decay rates of dead wood in a neotropical forest

Variation of dead wood decay rates among tropical trees remains one source of uncertainty in global models of the carbon cycle. Taking advantage of a broad forest plot network surveyed for tree mortality over a 23-year period, we measured the remaining fraction of boles from 367 dead trees from 26 neotropical species widely varying in wood density (0.23–1.24 g cm⁻³) and tree circumference at death time (31.5–272.0 cm). We modeled decay rates within a Bayesian framework assuming a first order differential equation to model the decomposition process and tested for the effects of forest management (selective logging vs. unexploited), of mode of death (standing vs. downed) and of topographical levels (bottomlands vs. hillsides vs. hilltops) on wood decay rates. The general decay model predicts the observed remaining fraction of dead wood (R ² = 60%) with only two biological predictors: tree circumference at death time and wood specific density. Neither selective logging nor local topography had a differential effect on wood decay rates. Including the mode of death into the model revealed that standing dead trees decomposed faster than downed dead trees, but the gain of model accuracy remains rather marginal. Overall, these results suggest that the release of carbon from tropical dead trees to the atmosphere can be simply estimated using tree circumference at death time and wood density.     

Investigation on catechin as a beech wood decay biomarker

A high-performance liquid chromatography (HPLC) method based on the evolution of wood extractives was developed to follow the first stages of fungal degradation of beech wood exposed to Coriolus versicolor. The nature and the quantity of the extracts initially present in wood depended on the extraction conditions and also on the wood-drying conditions (time and temperature). The most interesting fraction was soxhlet extracted with acetone at 56 °C for 6 h. The best conditions to avoid extractives degradation consisted of a moderate drying at 55 °C for 48 h allowing identification of catechin as potential tracer. After 2 weeks of wood blocks exposure to C. versicolor, analysis of their acetonic extractives showed that catechin signal initially detected in beech wood, had totally disappeared. Treatment of wood with an appropriate fungicide such as propiconazole before exposure to C. versicolor, prevents the catechin amount from any variation. The comparison of these results with the classical weight loss (WL) measurements obtained after long-time experiments on treated and untreated wood blocks shows that the catechin amount evolution, monitored during 2 weeks, correlates with the wood resistance evaluated during 16 weeks, allowing the use of this flavonoid as a valuable biomarker of wood decay.     

Greater accumulation of litter in spruce (Picea abies) compared to beech (Fagus sylvatica) stands is not a consequence of the inherent recalcitrance of needles

Background and aims

Replacement of beech by spruce is associated with changes in soil acidity, soil structure and humus form, which are commonly ascribed to the recalcitrance of spruce needles. It is of practical relevance to know how much beech must be admixed to pure spruce stands in order to increase litter decomposition and associated nutrient cycling. We addressed the impact of tree species mixture within forest stands and within litter on mass loss and nutritional release from litter.

Methods

Litter decomposition was measured in three adjacent stands of pure spruce (Picea abies), mixed beech-spruce and pure beech (Fagus sylvatica) on three nutrient-rich sites and three nutrient-poor sites over a three-year period using the litterbag method (single species and mixed species bags).

Results

Mass loss of beech litter was not higher than mass loss of spruce litter. Mass loss and nutrient release were not affected by litter mixing. Litter decay indicated non-additive patterns, since similar remaining masses under pure beech (47%) and mixed beech-spruce (48%) were significantly lower than under pure spruce stands (67%). Release of the main components of the organic substance (C_org, N_tot, P, S, lignin) and associated K were related to mass loss, while release of other nutrients was not related to mass loss.

Conclusions

In contradiction to the widely held assumption of slow decomposition of spruce needles, we conclude that accumulation of litter in spruce stands is not caused by recalcitrance of spruce needles to decay; rather adverse environmental conditions in spruce stands retard decomposition. Mixed beech-spruce stands appear to be as effective as pure beech stands in counteracting these adverse conditions.     

Genetic diversity and differentiation of <Emphasis Type="Italic">Fagus orientalis</Emphasis> Lipsky in Hyrcanian forests revealed by nuclear and chloroplast microsatellite markers

Oriental beech (Fagus orientalis Lipsky) is a widespread monoecious and wind-pollinated tree species. It is one of the major components of the Hyrcanian forests of Iran and it is of both ecological and economical importance. Twelve beech stands were surveyed at 9 chloroplast (cp) and 6 nuclear (n) polymorphic microsatellite loci (simple sequence repeats, SSR) to provide information on distribution of genetic diversity within and among populations and on gene conservation and silvicultural management of this species. High levels of genetic differentiation were detected for the chloroplast genome (F _ST = 0.80 and R _ST = 0.95), in sharp contrast to the nuclear genome (F _ST = 0.06, R _ST = 0.05). The analysis of molecular variance (AMOVA) showed that 48% of the total cpSSR variation was attributable to differences among regions and 30% to differences among populations within regions, suggesting multiple origins of beech populations in Hyrcanian forests. Nuclear SSRs confirmed the presence of significant differentiation among populations and among geographic regions, even if, as expected, this was less pronounced than that found with cpSSRs (based on AMOVA, differences among regions and among populations within regions each contribute 5% to total nSSR variance). A highly significant correlation between genetic (nSSRs) and geographic distances (R ² = 0.522) was estimated, thus showing an isolation by distance effect. The application of spatial analysis of molecular variance (SAMOVA) using both marker data allowed identification of genetically homogeneous groups of populations. Possible applications of these results for the certification of provenances and/or seed lots and for designing conservation programs are presented and discussed.     

Carbon preservation in humic lakes; a hierarchical regulatory pathway

Peatland catchments store vast amounts of carbon. Humic lakes and pools are the primary receptacles for terrigenous carbon in these meta‐ecosystems, representing sequestration hotspots; boreal lakes alone store ca. 120 Pg C. But little is known about the mechanisms that preserve aquatic carbon stocks. Here, we determined the regulatory pathway of decomposition in relation to ‘traditional’ limitations, namely anoxia, decay inhibiting compounds, low nutrients and acidity, using in vitro manipulation, mesocosms and natural gradients. We show that anoxia represents a powerful hierarchical preservation mechanism affecting all major limitations on decomposition and recapturing carbon that would otherwise escape from peatlands. Oxygen constraints on microbial synthesis of oxidases and nutrient‐cycling enzymes, prevents the decay of organic matter to CO₂, CH₄ and N₂O by allowing inhibitor accumulation and lowering nutrients. However, this pathway is sensitive to direct nutrient inputs and therefore eutrophication could initiate catastrophic feedback to global warming via dramatically increased greenhouse gas emissions. Identifying these process‐specific limitations should inform better management and conservation of these vital systems.     

Succession of saproxylic beetles associated with decomposition of boreal white spruce logs

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