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.     

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.     

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.     

Effects of temperature and litter type on fungal growth and decomposition of leaf litter

The dependence of fungal decomposition of leaf litter on incubation temperature and litter types used as substrata was assessed under pure culture conditions. Isolates of Xylaria sp., a major ligninolytic fungus in cool temperate forests in Japan, were used as the fungal material. Xylaria sp. is mesophilic; maximum growth and decomposition occurred at 25°C. In the temperature test, the decomposition pattern of beech leaf litter by three isolates of Xylaria sp. changed at a threshold at 25°C. Cellulolytic activity increased with temperature from 5 to 25°C, whereas above 25°C ligninolytic activity increased at the expense of cellulolytic activity, leading to suppressed overall decomposition as a result of the higher temperature. The mass loss of leaf litter caused at 20°C by an isolate of Xylaria sp. was variable among 15 litter types and was correlated negatively with acid-unhydrolyzable residue (AUR) content and positively with total carbohydrate content for the 15 litter types. The effects of temperature and litter type on the growth and decomposition of leaf litter by Xylaria sp. may have implications for changes in fungal decomposition of leaf litter that would be predicted in response to future environmental changes.     

Effects of prior decomposition of <Emphasis Type="Italic">Camellia japonica</Emphasis> leaf litter by an endophytic fungus on the subsequent decomposition by fungal colonizers

Effects of prior decomposition of Camellia japonica leaf litter by an endophytic phyllosphere fungus Coccomyces sp. on the subsequent decomposition of the litter by Coccomyces sp. and two succeeding fungi Dermateaceae sp. and Xylaria sp. (anamorph) were examined in a pureculture decomposition test. The prior decomposition of litter by Coccomyces sp. stimulated the subsequent decomposition by the three fungi. Dermateaceae sp. caused negligible weight loss on litter previously partly decomposed by Coccomyces sp. and then by Dermateaceae sp. and on litter decomposed singly by Dermateaceae sp. Xylaria sp. (anamorph) caused greater weight loss in these litters than control, uninoculated litter.     

Decomposition of litter in sub-alpine forests of Eucalyptus delegatensis,E. pauciflora and E. dives

The rate of decomposition of summer leaf-fall (abscised leaves), winter leaf-fall (containing some green leaves) and mature green (picked) leaves was assessed in sub-alpine forests of E. delegatensis (R. T. Baker), E. pauciflora (Sieb. ex Spreng) and E. dives (Schau.) in the Brindabella Range, Australian Capital Territory, using litter bag and tethered leaf techniques. The relative contribution of leaching, microbial respiration and grazing by invertebrate macrofauna to loss of leaf weight was determined. The effect of leaching and microbial respiration was assessed in terms of weight loss per unit area of leaf (specific leaf weight), while losses due to macro-faunal grazing were assessed by measuring reductions in leaf area. Litter decomposition constants for litter components (leaf, bark, wood) and total litter were determined from long-term records of litterfall and accumulated litter. Weight losses of abscised leaves during the initial 12 months ranged from 25% for E. pauciflora to 39% for E. delegatensis and were almost entirely due to reduction in specific leaf weight. Losses in the weight of leaves falling in winter ranged from 38 to 49%, while green leaves lost 45 - 59%. Approximately 50% of the total weight loss of green leaves was due to a loss in leaf area caused by skeletonization by litter macrofauna. Thus abscised leaves rather than green leaves must be used for measuring litter decomposition rates since abscised leaves constitute most of the litterfall in eucalypt forests. Leaves placed in the field in autumn decomposed slowly during the first summer, while the rate increased during the second winter and summer. Low litter moisture content appears to limit decomposition in the initial summer period in all communities, after which litterfall provides a mulch which reduces the rate of desiccation of lower litter layers. A simple linear regression model relating decomposition rate to the number of days (D) when litter moisture content exceeded 60% ODW accounted for 63-83% of the variation in decomposition of leaves in the field. Inclusion of mean monthly air temperature (T) and the product of D and T (day degrees when litter was wet) in a multiple linear regression increased the variation in decomposition accounted for to 80 – 90%. The rate of weight loss showed a positive linear relationship with the initial concentration of nitrogen (N) or phosphorus (P) in the leaf. These concentrations are an index of the decomposability of leaf substrates (e.g. degree of sclerophylly or lignification). The rate of loss of specific weight was similar for tethered leaves and for leaves enclosed in mesh bags. Measured loss in specific leaf weight after 70 – 90 weeks was less than that predicted using decomposition constants (k).     

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.     

Coarse Woody Debris Stimulates Soil Enzymatic Activity and Litter Decomposition in an Old-Growth Temperate Forest of Patagonia, Argentina

In most temperate forest ecosystems, tree mortality over time generates downed logs that accumulate as coarse woody debris (CWD) on the forest floor. These downed logs and trunks have important recognized ecosystem functions including habitat for different organisms and long-term organic C storage. Due to its recalcitrant chemical composition and slow decomposition, CWD can also have direct effects on ecosystem carbon and nutrient turnover. CWD could also cause changes indirectly through the physical and chemical alterations that it generates, although it is not well-understood how important these indirect effects could be for ecosystem processes and soil biogeochemistry. We hypothesized that in an old-growth mature forest, CWD affects carbon and nutrient cycles through its “proximity effects”, meaning that the forest floor near CWD would have altered soil biotic activity due to the environmental and biogeochemical effects of the presence of CWD. We conducted our study in an old-growth southern beech temperate forest in Patagonia, Argentina, where we estimated and classified the distribution and mass, nutrient pools and decay stage of CWD on the forest floor, and evaluated its impact on litter decomposition, soil mites and soil enzymatic activity of carbon and phosphorus-degrading enzymes. We demonstrate here that CWD in this ecosystem represents an important organic carbon reservoir (85 Mg ha^?1) and nitrogen pool (0.42 Mg ha^?1), similar in magnitude to other old-growth forests of the Northern Hemisphere. In addition, we found significant proximity effects of CWD, with increased C-degrading soil enzyme activity, decreased mite abundance, and more rapid litter decomposition beneath highly decayed CWD. Considered at the ecosystem scale in this forest, the removal of CWD could cause a decrease of 6% in soil enzyme activity, particularly in the summer dry season, and nearly 15% in annual litter decomposition. We conclude that beyond the established importance of CWD as a long-term carbon reservoir and habitat, CWD contributes functionally to the forest floor by influencing the spatial heterogeneity of microbial activity and carbon and nutrient turnover. These proximity effects demonstrate the importance of maintenance of this ecosystem component and should be taken into consideration for management decisions pertaining to carbon sequestration and functional diversity in natural forest ecosystems.     

Litter-dwelling beetles in primeval forests of Central Europe: Does deadwood matter?

We investigated the distribution pattern of litter dwelling beetles in four primeval forests of the Western Carpathians. The forests are situated in two mountain ranges and are either southerly exposed oak forests or northerly exposed beech forests. Beetles were extracted from leaf litter of plots close to coarse woody debris (c-CWD) and distant from coarse woody debris (d-CWD). We collected 2946 individuals of 172 species. Plots close to CWD usually were hot spots of species richness and beetle density, which could be increased two-fold and five-fold, respectively, when compared to d-CWD sites. The influence of CWD within each forest type was stronger than that of any other environmental factor. The c-CWD plots were characterised by both a higher presence of common species and a higher number of rare species. Especially, zoophagous and mycetophagous beetles were enhanced. The assemblage wide carrying capacity at c-CWD sites varied in respect to the gradients of temperature and moisture within a forest. A longer gradient provided a higher carrying capacity. We assume that the influence of downed deadwood on litter dwelling beetles will also be effective in commercial forests and stop the downward spiral with continuing loss of species.     

Decomposition of standing litter of the freshwater emergent macrophyte Juncus effusus

1. Standing dead plant litter of emergent macrophytes frequently constitutes a significant fraction of the detrital mass in many freshwater wetland and littoral habitats. Rates of leaf senescence and decomposition of the emergent macrophyte Juncus effusus were examined in a small freshwater wetland in central Alabama, U.S.A. Juncus effusus leaves in the initial stages of senescence were tagged in random plant tussocks and monitored periodically to determine in situ rates of leaf senescence and death. Fully senescent leaves were collected, placed in litter bags, and suspended above the sediments to simulate standing dead decay conditions. Litter bags were periodically retrieved over 2 years and analysed for weight loss, litter nutrient contents (N, P), associated fungal biomass and fungal taxa. 2. Senescence and death of J. effusus leaves proceeds from the leaf tip to the base at an exponential rate. The rate of senescence and death of leaf tissue increased with increasing temperatures. Plant litter decomposition was slow (k = 0.40 yr^–1), with 49% weight loss observed in 2 years. Both the nitrogen (N) and phosphorus (P) concentration (%) of litter increased during decomposition. However, the total amount of nitrogen (mg) in litter bags remained stable and phosphorus increased slightly during the study period. 3. Fungal biomass associated with plant litter, as measured by ergosterol concentrations, varied between 3 and 8% of the total detrital weight. Values were not significantly different among sampling dates (P > 0.05, ANOVA, Tukey). Fungi frequently identified on decaying litter were Drechslera sp., Conioscypha lignicola (Hyphomycetes), Phoma spp. (Coelomycetes), Panellus copelandii and Marasmiellus sp. (Basidiomycota). 4. These results support previous findings that plant litter of emergent macrophytes does not require submergence or collapse to the sediment surface to initiate microbial colonization and litter decomposition.     

Effects of Calcium on the Rate and Extent of Litter Decomposition in a Northern Hardwood Forest

Cross-site syntheses of litter decomposition studies have shown that litter calcium (Ca) concentration may have a role in controlling the extent of decomposition of tree foliage. We used an ongoing watershed CaSiO₃ addition experiment at the Hubbard Brook Experimental Forest in New Hampshire, USA, to test the hypotheses that increased Ca in litter would have no effect on the initial rates of litter decay but would increase the extent or completeness (limit value) of foliar litter decomposition. We tested these hypotheses with a 6-year litter decomposition experiment using foliar litter of four tree species that are prominent at this site and in the Northern Hardwood forest type of North America: sugar maple (Acer saccharum Marsh), American beech (Fagus grandifolia Ehrh.), yellow birch (Betula alleghaniensis Britt.), and white ash (Fraxinus americana L.). The experiment used a reciprocal transplant design with the Ca-treated watershed and a control site providing two sources of litter and two placement sites. The litter from the Ca-treated site was 10–92% higher in Ca concentration, depending on species, than the litter from the control site. After about 3 years of decomposition, the Ca concentrations in the litter reflected the placement of the litter (that is, the site in which it was incubated) rather than the source of the litter. The source of the litter had no significant effect on measures of initial decomposition rate, cumulative mass loss (6 years), or limit value. However, the placement of the litter had a highly significant effect on extent of decomposition. Some litter types responded more than others; in particular, beech litter placed in the Ca-treated site had a significantly higher limit value, indicating more complete decomposition, and maple litter in the Ca-treated site had a marginally higher limit value. These results indicate that Ca may influence the extent of litter decomposition, but it is the Ca at the incubation site rather than the initial litter Ca that matters most. The results also suggest that loss of Ca from the soil due to decades of acid deposition at this site may have impeded late-stage litter decomposition, possibly leading to greater soil C storage, especially in forest stands with a substantial component of beech. Likewise, de-acidification may lead to a reduction in soil C.     

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.     

Decomposition of organic chemical components in relation to nitrogen dynamics in leaf litter of 14 tree species in a cool temperate forest

Decomposition of lignin, holocellulose, polyphenols and soluble carbohydrates was investigated in relation to nitrogen (N) dynamics in leaf litter of 14 tree species. The influence of organic chemical components and N on litter mass loss rate was then evaluated for 14 litter types. The study was carried out over a 3-year period on upper and lower parts of a forest slope in a cool temperate forest in Japan. The decomposition processes were divided into early and late phases based on N immobilization and mobilization. Mass loss rate of whole litter and organic chemical components was similar for the upper and lower sites. Litter mass loss was faster in the immobilization phase than in the mobilization phase in each of 14 litter types, which was ascribed to the decreased mass loss of holocellulose, polyphenols and soluble carbohydrates in the mobilization phase as compared to the immobilization phase. Mass loss rate of lignin was not different between the phases. Litter mass loss rate in the immobilization and mobilization phases was negatively correlated to lignin content and positively correlated to contents of polyphenols and soluble carbohydrates at the start of these phases, but was not correlated to holocellulose and N contents in either phase.     

Leaf litter decomposition in temperate deciduous forest stands with a decreasing fraction of beech (Fagus sylvatica)

We hypothesised that the decomposition rates of leaf litter will increase along a gradient of decreasing fraction of the European beech (Fagus sylvatica) and increasing tree species diversity in the generally beech-dominated Central European temperate deciduous forests due to an increase in litter quality. We studied the decomposition of leaf litter including its lignin fraction in monospecific (pure beech) stands and in stands with up to five tree genera (Acer spp., Carpinus betulus, Fagus sylvatica, Fraxinus excelsior, Tilia spp.) using a litterbag approach. Litter and lignin decomposition was more rapid in stand-representative litter from multispecific stands than in litter from pure beech stands. Except for beech litter, the decomposition rates of species-specific tree litter did not differ significantly among the stand types, but were most rapid in Fraxinus excelsior and slowest in beech in an interspecific comparison. Pairwise comparisons of the decomposition of beech litter with litter of the other tree species (except for Acer platanoides) revealed a “home field advantage” of up to 20% (more rapid litter decomposition in stands with a high fraction of its own species than in stands with a different tree species composition). Decomposition of stand-representative litter mixtures displayed additive characteristics, not significantly more rapid than predicted by the decomposition of litter from the individual tree species. Leaf litter decomposition rates were positively correlated with the initial N and Ca concentrations of the litter, and negatively with the initial C:N, C:P and lignin:N ratios. The results support our hypothesis that the overall decomposition rates are mainly influenced by the chemical composition of the individual litter species. Thus, the fraction of individual tree species in the species composition seems to be more important for the litter decomposition rates than tree species diversity itself.     

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.     

Effects of attack of saprobic fungi on twig litter decomposition by endophytic fungi

Endophytic fungi of healthy twig tissues act as dominant primary colonizers of twig litters and are exposed to the attacks of saprobic secondary colonizers. In the present study, we examined the effect of interspecific interactions on the decay rate of twigs in laboratory experiments using two endophytic ascomycetes (Phomopsis sp. and Xylaria sp.) and two saprobic basidiomycetes (Mycena polygramma and Phanerochaete filamentosa) on twigs of Japanese beech (Fagus crenata) as a model system. Both endophytes were defensive against two saprobes on 2% malt agar, and were not replaced by the saprobes in the twigs during the incubation period. However, inoculation of the saprobes reduced the mass loss of twig components (acid-unhydrolyzable residue (AUR), holocellulose, soluble carbohydrate, and polyphenol). Especially when the twigs previously inoculated with Xylaria sp. or Phomopsis sp. were successively inoculated with M. polygramma the net weight of AUR increased, which was probably due to the synthesized melanin in hyphae of the endophytes. Our findings indicate that interspecific interactions between endophytic and saprobic fungi do affect the total mass of humic substances produced during the litter decay process.     

Beech log decomposition by wood-inhabiting fungi in a cool temperate forest floor: a quantitative analysis focused on the decay activity of a dominant basidiomycete <Emphasis Type="Italic">Omphalotus guepiniformis</Emphasis>

Wood decay activity of Omphalotus guepiniformis, one of the most frequently occurring fruiting bodies on beech coarse woody debris in cool temperate forests in Japan, was estimated in situ by chronosequence with a five decay class system. The decay columns of O. guepiniformis increased from decay class 1 to decay class 2, where they occupied 20.2% of the total area of cross sections, and was estimated to be a dominant basidiomycete. The decay columns of O. guepiniformis decreased after decay class 2 and were not detected in decay class 5. The relative density of the decay columns of O. guepiniformis decreased to 0.33 g cm⁻³ in decay class 2 (58.9% of fresh beech wood) but did not decrease thereafter. The lignocellulose index (LCI) of the decay columns of O. guepiniformis slightly decreased during the decay process while remaining in the range of white-rot. In contrast, the decay columns of microfungi increased in the later stages of decomposition and LCI of these decay columns decreased significantly alongside the decay process. These results suggest that O. guepiniformis has an important role in simultaneous decomposition of acid-unhydrolyzable residue (AUR, Klason lignin) and holocellulose in the early stages of beech log decomposition, while holocellulose selective decomposition by microfungi may occur in the late stages of decomposition.     

Exotic species as modifiers of ecosystem processes: Litter decomposition in native and invaded secondary forests of NW Argentina

Invasions of exotic tree species can cause profound changes in community composition and structure, and may even cause legacy effect on nutrient cycling via litter production. In this study, we compared leaf litter decomposition of two invasive exotic trees (Ligustrum lucidum and Morus sp.) and two dominant native trees (Cinnamomum porphyria and Cupania vernalis) in native and invaded (Ligustrum-dominated) forest stands in NW Argentina. We measured leaf attributes and environmental characteristics in invaded and native stands to isolate the effects of litter quality and habitat characteristics. Species differed in their decomposition rates and, as predicted by the different species colonization status (pioneer vs. late successional), exotic species decayed more rapidly than native ones. Invasion by L. lucidum modified environmental attributes by reducing soil humidity. Decomposition constants (k) tended to be slightly lower (−5%) for all species in invaded stands. High SLA, low tensile strength, and low C:N of Morus sp. distinguish this species from the native ones and explain its higher decomposition rate. Contrary to our expectations, L. lucidum leaf attributes were similar to those of native species. Decomposition rates also differed between the two exotic species (35% higher in Morus sp.), presumably due to leaf attributes and colonization status. Given the high decomposition rate of L. lucidum litter (more than 6 times that of natives) we expect an acceleration of nutrient circulation at ecosystem level in Ligustrum-dominated stands. This may occur in spite of the modified environmental conditions that are associated with L. lucidum invasion.     

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.