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.     

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.     

Asymbiotic Nitrogen Fixation and Litter Decomposition on a Long Soil-Age Gradient in Hawaiian Montane Rain Forest1

We determined rates of decomposition and asymbiotic nitrogen fixation in the leaf litter of Cheirodendron spp. on the Hawaiian Islands. Leaf litter was collected from four sites on a long soil-age gradient (300 yr to 4.1 M yr) and decomposed at two sites that differed widely in substrate age and nutrient availability. Rates of decomposition were higher in litter decomposed at the older site, where nutrient availability was greater. A substantial amount of nitrogen and phosphorus immobilization occurred in litter decomposed at the older site, with more immobilization occurring in litter with lower initial nitrogen and phosphorus concentrations, suggesting both supply and demand controls on nutrient immobilization. Potential rates of nitrogen fixation were very low in the first 25 d (0–5 nmol acetylene/gdw/h), rose to much higher rates by 70 d (20–45 nmol), and then declined by 140 d. We found no significant difference in rates of potential nitrogen fixation between sites of decomposition, but there was a strong substrate effect, with higher rates in litter with low lignin, low nitrogen, and high phosphorus. Where significant immobilization of nitrogen occurred for decomposing Cheirodendron, nitrogen fixation could have comprised no more than 10 percent of immobilized nitrogen. Overall, rates of nitrogen fixation were dependent on the source of the decomposing substrate but not on the site of decomposition, while short-term decomposition and nutrient immobilization were strongly dependent on the site of decomposition but not as much on the source of the decomposing substrate.     

Comparison of litter decomposing ability among diverse fungi in a cool temperate deciduous forest in Japan

The litter decomposing ability of 79 fungal isolates (41 genera, 60 species) was assessed with the pure culture decomposition test. The isolates were collected qualitatively in a cool temperate deciduous forest in Japan during a 21-mo period. Loss of original weight of sterilized litter ranged from 0.1% to 57.6%. Six isolates in the Basidiomycota caused high weight losses ranging from 15.1% to 57.6%. Fourteen isolates in Xylaria and Geniculosporium (the Xylariaceae and its anamorph) also caused high weight losses ranging from 4.0% to 14.4%. Other isolates in the Ascomycota and associated anamorphs and in the Zygomycota caused low weight losses on mean. Six fungi in the Basidiomycota, and all in the Xylariaceae showed a bleaching activity of the litter and caused lignin and carbohydrate decomposition. Mean lignin/weight loss ratios (L/W) and lignin/carbohydrate loss ratios (L/C), were 0.9 and 0.7 for the Basidiomycota and 0.7 and 0.4 for the Xylariaceae, respectively. Significant differences were found in L/W and L/C between the two groups when the result of Xylaria sp. that showed marked delignification was excluded. These differences in lignin and carbohydrate utilization patterns are discussed in relation to the structural and the chemical properties of the decomposed litter and to the implications for organic chemical changes during litter decomposition processes.     

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.     

Accumulation and release of nitrogen and phosphorus in relation to lignin decomposition in leaf litter of 14 tree species

Immobilization and mobilization of nitrogen and phosphorus were investigated in relation to the nitrogen (L/N) ratio and lignin to the phosphorus (L/P) ratio as indicators of the nitrogen and phosphorus dynamics. The present study was carried out on upper and lower parts of a forest slope in a cool temperate forest in Japan. Net immobilization and net mobilization characterized the dynamics of nitrogen and phosphorus in 14 litter types and were related to the changes in the L/N and L/P ratio. The critical values of the L/N and L/P ratio at which the mobilization began were 23–25 and 500–620, respectively. In litter types with the L/N and L/P ratio higher than critical values, nitrogen and phosphorus were immobilized until the ratios reached at the critical values and then nitrogen and phosphorus began decreasing. In litter types with initial L/N and L/P ratios lower than or equal to the critical values, nitrogen and phosphorus were released from litter. The critical values of the L/N and L/P ratios showed convergent trends among litter types as compared to their initial values, and were approached to those of underlying humus layers. These results indicated the usefulness of L/N and L/P ratios as indicators of the nitrogen and phosphorus dynamics in the study site. The general validity of the L/N ratio as an indicator of nitrogen dynamics and the convergent trend of critical L/N ratio at 25–30 were demonstrated by a review of literature on lignin and nitrogen dynamics in 47 litter types in temperate and boreal forests.     

Nitrogen availability affects saprotrophic basidiomycetes decomposing pine needles in a long term laboratory study

Fungi, especially basidiomycetous litter decomposers, are pivotal to the turnover of soil organic matter in forest soils. Many litter decomposing fungi have a well-developed capacity to translocate resources in their mycelia, a feature that may significantly affect carbon (C) and nitrogen (N) dynamics in decomposing litter. In an eight-month long laboratory study we investigated how the external availability of N affected the decomposition of Scots pine needles, fungal biomass production, N retention and N-mineralization by two litter decomposing fungi – Marasmius androsaceus and Mycena epipterygia. Glycine additions had a general, positive effect on fungal biomass production and increased accumulated needle mass loss after 8 months, suggesting that low N availability may limit fungal growth and activity in decomposing pine litter. Changes in the needle N pool reflected the dynamics of the fungal mycelium. During late decomposition stages, redistribution of mycelium and N out from the decomposed needles was observed for M. epipterygia, suggesting autophagous self degradation.     

A 5 year study of litter decomposition processes in aChamaecyparis obtusa Endl. forest

Decomposition of needle litter in aChamaecyparis obtusa forest was studied over a 5 year period using a litter bag method. Organic matter, nitrogen and carbon mass and faunal abundance were monitored. The pattern of weight loss was represented by three phases: the initial leaching of carbon and nitrogen (0–3 months), nitrogen immobilization (3–15 months), and nitrogen mobilization (15–60 months). The decomposition rate of needle litter was expressed by Olson's decomposition constant (k) which was−0.113 over a 5 year period. The decomposition rate decreased with the advance of decomposition processes. The role of soil fauna in the decomposition process was assessed by comparing decomposition rates between the control and defaunated plots. In the leaching phase, soil animals had no significant role in the decomposition processes. During the immobilization phase, soil animals contributed to the immobilization processes through their grazing activities, and there were significant differences in weight loss between the control and defaunated plots. In the mobilization phase, saprovorous soil animals such as Collembola and Acari contributed to the mobilization processes by feeding on decomposing litter. Decomposition processes observed in this study were compared with other similar studies.     

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.     

Phyllosphere fungi on living and decomposing leaves of giant dogwood

Phyllosphere fungi on living leaves and their succession on decomposing leaves were studied on giant dogwood (Swida controversa). A total of 12 and 34 fungal species were isolated from the interior and surface, respectively, of living leaves, and 15 frequent species were considered as phyllosphere fungi. Six of these 15 species were also frequent on decomposing litter. Characteristic successional trends were observed in the 6 phyllosphere fungi during decomposition. The sum of frequencies of endophytes decreased as decomposition progressed, and no endophytes were isolated from the litter at the 11th month of decomposition. The sum of frequencies of epiphytes increased as decomposition progressed. Endophytes and epiphytes showed different responses to litter mass loss and concentrations of nitrogen, lignin, and total carbohydrates during the decomposition process. These results suggested that epiphytes may survive on decomposing leaves as primary decomposers on the ground, thereby excluding endophytes by competition for available energy sources, and that epiphytes may have a greater contribution to decomposition than endophytes in dogwood leaves.     

Mass loss and nitrogen dynamics in decomposing acid forest litter in the Netherlands at increased nitrogen deposition

Litterbag experiments were carried out in five forest ecosystems in the Netherlands to study weight loss and nitrogen dynamics during the first two years of decomposition of leaf and needle litter. All forests were characterized by a relatively high atmospheric nitrogen input by throughfall, ranging from 22–55 kg N ha^–1 yr^–1.Correlation analysis of all seven leaf and needle litters revealed no significant relation between the measured litter quality indices (nitrogen and lignin concentration, lignin-to-nitrogen ratio) and the decomposition rate. A significant linear relation was found between initial lignin-to-nitrogen ratio and critical nitrogen concentration, suggesting an effect of litter quality on nitrogen dynamics.Comparison of the decomposition of oak leaves in a nitrogen-limited and a nitrogen-saturated forest suggested an increased nitrogen availability. The differences in capacities to retain atmospheric nitrogen inputs between these two sites could be explained by differences in net nitrogen immobilization in first year decomposing oak leaves: in the nitrogen-limited oak forest a major part (55%) of the nitrogen input by throughfall was immobilized in the first year oak leaf litter.The three coniferous forests consisted of two monocultures of Douglas fir and a mixed stand of Douglas fir and Scots pine. Despite comparable litter quality in the Douglas fir needles in all sites, completely different nitrogen dynamics were found.     

Diversity and host recurrence of fungi associated with the bleached leaf litter in a subtropical forest

Fungi that selectively remove lignin cause extensive bleaching of leaf litter, which results in the acceleration of litter decomposition. The taxonomic diversity and host recurrence of saprotrophic fungi associated with bleached leaf litter were investigated in a subtropical forest in southern Japan. A total of 211 fungal isolates and sporocarps were obtained from bleached portions of leaf litter of 33 plant species in 18 families and were classified into 83 operational taxonomic units (OTUs) at the 97% similarity level of the ITS rDNA sequence. These fungal OTUs belonged to Rhytismataceae and Xylariaceae in the Ascomycota, and Marasmiaceae, Mycenaceae, Lachnocladiaceae, and Physalacriaceae in the Basidiomycota. OTUs in Rhytismataceae and Marasmiaceae showed a significantly higher degree of recurrence for plant species than simulated networks where partners were associated randomly. In contrast, OTUs in Xylariaceae and Mycenaceae showed no significant recurrence for plant species. Such differing degrees of recurrence for plant species implied different roles of fungal families in leaf litter decomposition.     

Nitrogen immobilization in leaf litter at two Mediterranean ecosystems of SW Spain

Nitrogen immobilization in relation to the dynamics of lignin and tannins in nine different types of leaf litter was investigated during a 2-yr study at two Mediterranean ecosystems of SW Spain. Net nitrogen immobilization for all the species was higher in a forest than in the more nutrient-poor soil of a shrubland. Absolute amount of lignin increased in both ecosystems in the first 2–4 months whereas tannin rapidly decreased in the same time period. Increases in lignin were significantly correlated to losses of tannins during decomposition. Initial tannin content was the best predictor of the maximum amount of immobilized nitrogen in litter in both ecosystems. Mechanisms that could explain the immobilization of nitrogen in litter are discussed.     

Lignin and nitrogen in the decomposition of leaf litter in a sub-tropical forest ecosystem at Shiroy hills in north-eastern India

The effect of the initial lignin and nitrogen contents of the leaves of five tree species, on their decomposition dynamics, was studied in the sub-tropical forest ecosystem existing at Shiroy hills. The decomposition dynamics of litter materials are described by inverse linear relationships between the percentage of the original biomass remaining and the nitrogen concentration in the residual material. Initial lignin and nitrogen were highly correlated with remaining biomass (r=0.94 and 0.77). The rate constants (K), for the annual leaf mass loss, ranged from −0.18 to −0.56. The values for initial lignin (%), initial nitrogen (%), the ratio between initial lignin, initial nitrogen and the annual decomposition rate constants were compared with similar results from other studies in various climatic zones of the world.     

Cellulose utilization in forest litter and soil: identification of bacterial and fungal decomposers

Organic matter decomposition in the globally widespread coniferous forests has an important role in the carbon cycle, and cellulose decomposition is especially important in this respect because cellulose is the most abundant polysaccharide in plant litter. Cellulose decomposition was 10 times faster in the fungi-dominated litter of Picea abies forest than in the bacteria-dominated soil. In the soil, the added (13)C-labelled cellulose was the main source of microbial respiration and was preferentially accumulated in the fungal biomass and cellulose induced fungal proliferation. In contrast, in the litter, bacterial biomass showed higher labelling after (13)C-cellulose addition and bacterial biomass increased. While 80% of the total community was represented by 104-106 bacterial and 33-59 fungal operational taxonomic units (OTUs), 80% of the cellulolytic communities of bacteria and fungi were only composed of 8-18 highly abundant OTUs. Both the total and (13)C-labelled communities differed substantially between the litter and soil. Cellulolytic bacteria in the acidic topsoil included Betaproteobacteria, Bacteroidetes and Acidobacteria, whereas these typically found in neutral soils were absent. Most fungal cellulose decomposers belonged to Ascomycota; cellulolytic Basidiomycota were mainly represented by the yeasts Trichosporon and Cryptococcus. Several bacteria and fungi demonstrated here to derive their carbon from cellulose were previously not recognized as cellulolytic.     

Interacting Microbe and Litter Quality Controls on Litter Decomposition: A Modeling Analysis

The decomposition of plant litter in soil is a dynamic process during which substrate chemistry and microbial controls interact. We more clearly quantify these controls with a revised version of the Guild-based Decomposition Model (GDM) in which we used a reverse Michaelis-Menten approach to simulate short-term (112 days) decomposition of roots from four genotypes of Zea mays that differed primarily in lignin chemistry. A co-metabolic relationship between the degradation of lignin and holocellulose (cellulose+hemicellulose) fractions of litter showed that the reduction in decay rate with increasing lignin concentration (LCI) was related to the level of arabinan substitutions in arabinoxylan chains (i.e., arabinan to xylan or A∶X ratio) and the extent to which hemicellulose chains are cross-linked with lignin in plant cell walls. This pattern was consistent between genotypes and during progressive decomposition within each genotype. Moreover, decay rates were controlled by these cross-linkages from the start of decomposition. We also discovered it necessary to divide the Van Soest soluble (labile) fraction of litter C into two pools: one that rapidly decomposed and a second that was more persistent. Simulated microbial production was consistent with recent studies suggesting that more rapidly decomposing materials can generate greater amounts of potentially recalcitrant microbial products despite the rapid loss of litter mass. Sensitivity analyses failed to identify any model parameter that consistently explained a large proportion of model variation, suggesting that feedback controls between litter quality and microbial activity in the reverse Michaelis-Menten approach resulted in stable model behavior. Model extrapolations to an independent set of data, derived from the decomposition of 12 different genotypes of maize roots, averaged within <3% of observed respiration rates and total CO₂ efflux over 112 days.     

不同树叶凋落物对人参土壤理化性质及微生物群落结构的影响

树种选择是林下山参护育成败的关键,研究树叶凋落物对人参土壤养分、微生物群落结构组成的影响,旨在为林下山参护育选择适宜林地及农田栽参土壤改良提供科学依据和理论指导。通过盆栽试验,研究添加5.0 g色木槭Acer mono.Maxim.var.mono(A)、赤松Pinus densiflora Sieb.et Zucc.(B)、胡桃楸Juglans mandshurica Maxim.(C)、紫椴Tilia amurensis Rupr.(D)、蒙古栎Quercus mongolica Fisch.ex Ledeb.(E)树叶凋落物到土壤中,种植人参(Panax ginseng C.A.meyer)后研究土壤理化性质以及微生物群落结构的变化。结果表明:添加不同树叶处理后人参土壤性质发生改变,土壤p H值显著高于对照土壤5.91(P0.05),土壤全氮、速效氮磷、微生物碳氮在所有树叶处理中显著增加(P0.05),而土壤容重、速效钾和C/N在添加树叶处理中降低。18个土壤样品基因组,经16S和ITS1测序分别得到6064和1900个OUTs。其中细菌涵盖了42门、117纲、170目、213科、225属,真菌涵盖了24门、98纲、196目、330科、435属。不同树叶处理人参土壤细菌和真菌地位发生改变,细菌Proteobacteria是树叶分解的关键微生物,添加树叶后其多样性显著高于对照(P0.05)。而细菌Bacteroidetes和真菌Basidiomycota可能是区别阔叶林和针叶林树种的关键微生物,针叶林中含量显著低于阔叶林(P0.05),而真菌Ascomycota是针叶林分解的关键微生物。进一步从不同分类水平上得到特定树叶凋落物的特异细菌和真菌。典型相关分析(CDA)表明细菌Bacteroidetes、Chloroflexi、Actinobacteria及真菌Basidiomycota、Zygomycota、Chytridiomycota及Ascomycota的位置及多样性的改变均与土壤因子SMBN、TN、AP、SOC、AK、C/N、p H有关。综上所述,添加不同树叶后不仅提高土壤微生物量碳氮、改善土壤理化性质,同时改变微生物群落结构组成,不同树叶处理土壤理化性质不同导致人参土壤微生物组成的差异,本结果对于林下参选地和农田栽参土壤微生物改良具有理论指导作用。     

Microbial Colonization of Beech and Spruce Litter—Influence of Decomposition Site and Plant Litter Species on the Diversity of Microbial Community

The present study was conducted to investigate the effect of decomposition site and plant litter species on the colonizing microbial communities. For this, litter bag technique using beech and spruce litter was combined with RNA-based fingerprinting and cloning. Litter bags were incubated for 2 and 8 weeks in the A_h horizon of beech and beech–spruce mixed forest sites. Although sugars and starch were rapidly lost, lignin content increased by more than 40% for beech and more than doubled for spruce litter at both soil sites at the end of the experiment. Denaturing gradient gel electrophoresis analysis of 16S and 18S rRNA RT–PCR products was used for screening of differences between bacterial and fungal communities colonizing the two litter types. Development of the microbial community over time was observed to be specific for each litter type and decomposition site. RT–PCR products from both litter types incubated in beech–spruce mixed forest site were also cloned to identify the bacterial and fungal colonizers. The 16S rRNA clone libraries of beech litter were dominated by γ-proteobacterial members, whereas spruce libraries were mainly composed of α-, β-, and γ-proteobacterial members. Ascomycota members dominated the 18S rRNA clone libraries. Clones similar to Zygomycota were absent from spruce, whereas those similar to Basidiomycota and Glomeromycota were absent from beech libraries. Selective effects of litter quality were observed after 8 weeks. The study provides an insight into the bacterial and fungal communities colonizing beech and spruce litter, and the importance of litter quality and decomposition site as key factors in their development and succession.     

Nutrient release from decomposing leaf litter of Banksia ornata,Dark Island heathland,South Australia

Distinct O₁ and O₂ layers, representing annual litter fall, enabled the sequential loss of biomass and nutrients (phosphorus and nitrogen) to be reconstructed in undisturbed litter layers of Banksia ornata in the Dark Island heathland, South Australia. Apart from an initial loss in biomass and nitrogen, the dry weight and nutrient content of the O₁ layer, exposed to the desiccating influence of the atmosphere, remained relatively constant until covered by the following year's leaf fall. Under the blanket of newly fallen leaves, biomass decomposition proceeded continuously through autumn, winter, spring, into the dry summer season. Even though the biomass of the decomposing leaf (O₂) layer decreased continuously, its nutrient content remained relatively constant until the summer season was reached when total decomposition and nutrient loss occurred. During spring, fine rootlets invaded the decomposing litter layer (O₂) and, together with decomposer fungi, bacteria and soil fauna, maintained the total nutrient content of the decomposing leaf at a constant level. By late spring-early summer shoot growth of the dominant heath species was initiated, inducing the mobilization of the nutrients stored in the decomposing litter layer.