Interactions between litter quality, decomposition and soil fertility: a laboratory study

Leaf litters from beech (Fagus sylvatica L.) and oak (Quercus robur L.) trees were collected from mixed, deciduous woodlands growing on three soil types that varied in mineral nutrient concentrations and N mineralisation potential. Litter quality, including %N, %Mn, %P, acid detergent fibre, cellulose, Klason lignin, phenylpropanoid constituents of lignin, hexose and pentose sugar (mainly from hemicelluloses) varied within species according to soil type. However, oak and beech showed the opposite responses to soil nutrient status for most of these variables. The litters were incubated in the laboratory for 12 months (at 18 °C and constant moisture) on beds of forest floor material from two soils of contrasting high nutrient material (HNM) or low nutrient material (LNM) nutrient status to investigate litter quality and substrate interactions. At 4, 8 and 12 months there were significant differences in mass losses from oak and beech litters from all sites, and for each litter type exposed to the HNM and LMN soils. At 12 months mean mass losses were higher for HNM treatment (38.7% oak, 27.8% beech) than for the LNM treatment (30.6% oak, 25.5% beech). However, the beech and oak litters from the different sites consistently responded in opposite ways on the same soil treatment reflecting site-related effects on litter quality. Initial concentration of Klason lignin was the best predictor for mass losses from litter species and litter types. Intra-specific variation in rates of litter decomposition of beech and oak litters from different sites, and differences in their interactions with the two forest floor materials, illustrate the complexities of proximate controls on decomposition that are often masked in system-level studies.     

Release and retention patterns of organic compounds and nutrients after the cold period in foliar litterfall of pure European larch,common beech and red oak plantations in Lithuania

This study was carried out in alien warmth-tolerant forest plantations of red oak (Quercus rubra), common beech (Fagus sylvatica) and European larch (Larix decidua). We compared the changes in foliar litterfall mass and biochemical composition after five months of cold period. The mean mass of fresh foliar litterfall collected in late autumn was 30% higher in red oak compared to the larch and beech plantations. After the cold period, the reduction of foliar litterfall mass did not exceed 10% in any of the studied plantations. The fresh foliar litterfall of red oak was the richest in cellular fibre and easily decomposable glucose and nutrients such as P and Mg, larch was distinguished by the highest lignin, N, K and Ca concentrations, while beech fresh foliar litterfall was the poorest in the aforementioned nutrients. After the cold period, the changes in the biochemical composition of foliar litterfall revealed different patterns. In the spring, the beech and red oak foliar litterfall was the richest in N, P and Ca, meanwhile the larch foliar litterfall still had the highest concentration of lignin but, in contrast to the autumn, was the poorest in nutrients. After the cold period Lignin: N, C: N and C: P ratios reached critical values indicating that the foliar litterfall of beech and red oak had started to decompose. The highest lignin concentration and the highest and most stable Lignin: N, C: N, C: P and N: P ratios after the cold period indicated that the slowest foliar litterfall decomposition took place in the larch plantation.     

Partitioning of carbon and nitrogen during decomposition of 13C15N‐labeled beech and ash leaf litter

The aim of this study was to determine the influence of leaf‐litter type (i.e., European beech—Fagus sylvatica L. and European ash—Fraxinus excelsior L.) and leaf‐litter mixture on the partitioning of leaf‐litter C and N between the O horizon, the topsoil, the soil microbial biomass, and the CO₂ emission during decomposition. In a mature beech stand of Hainich National Park, Thuringia, Germany, undisturbed soil cores (?? 24 cm) were transferred to plastic cylinders and the original leaf litter was either replaced by ¹³C¹⁵N‐labeled beech or ash leaf litter, or leaf‐litter‐mixture treatments in which only one of the two leaf‐litter types was labeled. Leaf‐litter‐derived CO₂‐C flux was measured every second week over a period of one year. Partitioning of leaf‐litter C and N to the soil and microbial biomass was measured 5 and 10 months after the start of the experiment. Ash leaf litter decomposed faster than beech leaf litter. The decomposition rate was negatively related to initial leaf‐litter lignin and positively to initial Ca concentrations. The mixture of both leaf‐litter types led to enhanced decomposition of ash leaf litter. However, it did not affect beech leaf‐litter decomposition. After 5 and 10 months of in situ incubation, recoveries of leaf‐litter‐derived C and N in the O horizon (7%–20% and 9%–35%, respectively) were higher than in the mineral soil (1%–5% and 3%–8%, respectively) showing no leaf‐litter‐type or leaf‐litter‐mixture effect. Partitioning of leaf‐litter‐derived C and N to microbial biomass in the upper mineral soil (< 1% of total leaf‐litter C and 2%–3% of total leaf‐litter N) did not differ between beech and ash. The results show that short‐term partitioning of leaf‐litter C and N to the soil after 10 months was similar for ash and beech leaf litter under standardized field conditions, even though mineralization was faster for ash leaf litter than for beech leaf litter.     

Elevated CO<Subscript>2</Subscript> concentration affected pine and oak litter chemistry and the respiration and microbial biomass of soils amended with these litters

Elevated atmospheric CO₂ concentration ([CO₂]) may change litter chemistry which affects litter decomposability. This study investigated respiration and microbial biomass of soils amended with litter of Pinus densiflora (a coniferous species; pine) and Quercus variabilis (a deciduous species; oak) that were grown under different atmospheric [CO₂] and thus had different chemistry. Elevated [CO₂] increased lignin/N through increased lignin concentration and decreased N concentration. The CO₂ emission from the soils amended with litter produced under the same [CO₂] regime was greater for oak than pine litter, confirming that broadleaf litter with lower lignin decomposes faster than needle leaf litter. Within each species, however, soils amended with high lignin/N litter grown under elevated [CO₂] emitted more CO₂ than those with low lignin/N litter grown under ambient [CO₂]. Such contrasting effects of lignin/N on inter- and intra-species variations in litter decomposition should be ascribed to the effects of other litter chemistry variables including nonstructural carbohydrate, calcium and manganese as well as inhibitory effect of N on lignin decomposition. The microbial biomass was also higher in the soils amended with high lignin/N litter than those with low lignin/N litter probably due to low substrate use efficiency of lignin by microbes. Our study suggests that elevated [CO₂] increases lignin/N for both species, but increased lignin/N does not always reduce soil respiration and microbial biomass. Further study investigating a variety of tree species is required for more comprehensive understanding of inter- and intra-species variations of litter decomposition under elevated [CO₂].     

Adsorption of cellulase components by leaf litter

The competitive adsorption of Trichoderma viride cellulase components to leaf litter was investigated to further elucidate the role of extracellular enzymes as mediators of decomposition processes. Litter analogs were prepared by acid-detergent digestion of senescent Pinus strobus (white pine), Quercus prinus (chestnut oak) and Cornus florida (flowering dogwood) leaves. Enzymatic cellulose digestion was used to produce litter analogs of higher lignin content. The white pine litter analogs had a high affinity for exocellulase and β-glucosidase. Chestnut oak litter preferentially bound endocellulase components and flowering dogwood litter displayed intermediate trends. Natural mixed-deciduous and white pine litters and humus had less capacity for immobilizing cellulase components. The adsorption data are consistent with available information on the binding of cellulase components to purified cellulose and with information on the cellulase activity patterns of decomposing leaf litter.     

Decomposing ability of interior and surface fungal colonizers of beech leaves with reference to lignin decomposition

Fungi were isolated from interior and surface of beech (Fagus crenata Blume) leaf litter by surface sterilization and washing methods. Species composition differed between the interior and surface of the leaves. Xylaria sp. (anamorph) was a major interior colonizer, while Pestalotiopsis spp. and Trichoderma spp. were predominantly surface colonizers. Ascochyta sp. was isolated from both the interior and surface of leaves. Leaf litter decomposing abilities of all isolated species were assessed by pureculture decomposition tests. Changes in lignin, carbohydrate and polyphenol amounts in the litter were investigated. Percent loss of original weight of sterilized beech leaf litter ranged from 0.24 to 11.16 % in the decomposition test. Interior fungi such as Xylaria sp. (anamorph) had the highest abilities to bleach leaf litter and decompose lignin. Most surface fungi had limited ability to decompose leaf litter and lignin. The difference in the decomposing abilities between the interior and surface fungi is discussed in relation to the difference in organic-chemical compositions between interior and surface of the litter.     

Changes in soil microbial substrate utilization in response to altered litter diversity and precipitation in a Mediterranean shrubland

This study aimed at quantifying the consequences of reduced precipitation and plant diversity on soil microbial community functioning in a Mediterranean shrubland of southern France. Across a natural gradient of shrub species diversity, we established a total of 92 plots (4 × 4 m) with and without a moderate rain exclusion treatment of about 12 % of total precipitation. Shrub diversity included all possible combinations of the four dominant species (Cistus albidus, Quercus coccifera, Rosmarinus officinalis, and Ulex parviflorus). Respective leaf litter mixtures of these species combinations were exposed in all plots over 2 years. We quantified how litter species richness and the reduction in precipitation affected the soil microbial substrate utilization (measured by CO₂ evolution using the MicroResp method) on soil samples collected underneath each individual litter mixture after 1 and 2 years of decomposition. Moderate precipitation reduction had a minor impact, but litter species richness and the dissimilarity in phenolic concentrations (estimated using Rao’s quadratic entropy) showed a positive effect on the diversity of substrates metabolized by the microbial communities. Moreover, litter species richness increased soil microbial activity by increasing the catabolic diversity of the soil microbial community. These effects were mostly driven by the presence of Quercus and Ulex leaf litter, which at the same time reduced microbial metabolic dominance, while the presence of Rosmarinus had opposite effects. Our data suggest that plant species loss can have stronger effects on the functioning of soil microbial communities than moderate drought, with potentially important feedbacks on biogeochemical cycling in Mediterranean shrubland ecosystems.     

Effects of tree species and topography on soil chemistry, litter quality, and decomposition in Northeast Turkey

Leaf litters from beech (Fagus orientalis Lipsky.) and oak (Quercus robur L.), and needle litters from fir (Abies nordmanniana Spach.) and pine (Pinus sylvestris L.) trees were collected from north-facing site and south-facing site and at three slope positions (top, middle and bottom) on each aspect that varied in soil chemical characteristics (soil pH, cation exchange capacity and base saturation). The litters were analysed for initial total carbon, nitrogen, acid detergent fibre, lignin and cellulose concentrations. Nitrogen, acid detergent fibre and lignin concentrations and carbon:nitrogen and lignin:nitrogen ratios varied significantly within and between species according to soil chemical characteristics on aspects and slope positions. Litter decomposition was studied in the field using the litterbag technique. The litters were placed on two aspects and at three slopes on each aspect in October 2001, and were sampled every 6-month for 2 years. The main effects of aspect, species and slope position on decomposition rates were all statistically significant. Oak leaf litter showed highest decomposition rates, followed by pine, fir and beech litter, and the litters placed on north-facing site decomposed faster than those on the south-facing site. The litters placed at the top slope position decomposed slower than at those at either the bottom or middle positions. Initial lignin concentrations explained most of the variation in decomposition rates between species, and within species for the aspects and the slope positions, but the explained variance showed differences between aspects and slope positions. This result illustrates the important point that litter quality may define the potential rates of microbial decomposition but these are significantly influenced by the biotic and abiotic environment in which decomposition takes place.     

Effect of temperature and moisture on the mineralization and humification of leaf litter in a model incubation experiment

The mineralization and humification of leaf litter collected in a mixed forest of the Prioksko-Terrasny Reserve depending on temperature (2, 12, and 22°C) and moisture (15, 30, 70, 100, and 150% of water holding capacity ( WHC)) has been studied in long-term incubation experiments. Mineralization is the most sensitive to temperature changes at the early stage of decomposition; the Q ₁₀ value at the beginning of the experiment (1.5–2.7) is higher than at the later decomposition stages (0.3–1.3). Carbon losses usually exceed nitrogen losses during decomposition. Intensive nitrogen losses are observed only at the high temperature and moisture of litter (22°C and 100% WHC). Humification determined from the accumulation of humic substances in the end of incubation decreases from 34 to 9% with increasing moisture and temperature. The degree of humification C_HA/C_FA is maximum (1.14) at 12°C and 15% WHC; therefore, these temperature and moisture conditions are considered optimal for humification. Humification calculated from the limit value of litter mineralization is almost independent of temperature, but it significantly decreases from 70 to 3% with increasing moisture. A possible reason for the difference between the humification values measured by two methods is the conservation of a significant part of hemicelluloses, cellulose, and lignin during the transformation of litter and the formation of a complex of humic substances with plant residues, where HSs fulfill a protectoral role and decrease the decomposition rate of plant biopolymers.     

Feeding preferences of native terrestrial isopod species (Oniscoidea,Isopoda) for native and introduced leaf litter

Due to current predictions for Central Europe that forecast higher frequencies of hot and dry summers, Mediterranean drought-tolerant oak species are being evaluated as future forest trees for German forest sites that are becoming increasingly damaged by water deficit. As a result of planting foreign tree species, the leaf litter composition and thus the food resources of native saprophagous macroarthropods will change, possibly altering primary decomposition processes. Therefore, experiments concerning the acceptance and palatability of introduced versus native litter for native isopods were undertaken. Consumption rates of four native isopod species (Porcellio scaber, Oniscus asellus, Trachelipus rathkii, Trachelipus ratzeburgii) were investigated in laboratory choice tests with introduced (Quercus pubescens, Quercus frainetto, Quercus ilex) and comparable native (Fagus sylvatica, Quercus robur) leaf litter. Litter was characterized by measurement of C/N-ratios and lignin content. Although species-specific preferences of isopods could be observed in the experiments, Mediterranean oak litter was consumed by all investigated species. Furthermore, two isopod species even preferred the leaf litter of the introduced Q. ilex. Compared to native beech or oak litter, litter from these introduced tree species thus apparently do not negatively influence the consumption rates of terrestrial isopods. Possible reasons for the determined preferences are discussed.     

Decomposition of tree leaf litter and crop residues from ginkgo agroforestry systems in Eastern China: an in situ study

Purpose

Litter decomposition is a crucial biogeochemical process linking nutrient cycling and carbon (C) storage in ecosystems, but few studies have investigated this process in agroforestry systems, where tree leaf litter is mixed with intercrop residues.

Materials and methods

A 360-day in situ litter bag decomposition experiment was conducted in three ginkgo (Ginkgo biloba L.) plantation systems (a ginkgo-corn (Zea mays L.)-wheat (Triticum aestivum L.) system, ginkgo-rape (Brassica napus L.)-soybean (Glycine max (L.) Merr.) system, and pure ginkgo system).

Results and discussion

Ginkgo leaves decomposed fastest in the ginkgo-corn-wheat system, followed by the ginkgo-soybean-rape system, and the pure ginkgo system. Among all litter species, corn leaves and a ginkgo-corn mixture in the ginkgo-corn-wheat system decomposed fastest and wheat straw most slowly. The Olson’s litter exponential decay model showed the same results; approximately 9 months and slightly less than 27 months was required to decompose 50 and 95% of the litter, respectively. Compared to single-species litter, mixed litters accelerated litter decomposition, except for the ginkgo-wheat mixture. Litter nitrogen (N) loss varied dramatically among litter species during the 360-day in situ incubation.

Conclusions

The agroforestry system, litter quality, and mixed effects play important roles in litter decomposition. The Ca content, organic carbon, and living vegetation should be taken into account when studying litter decomposition in agroforestry. Analysis during the litter decomposition process clearly indicated that litter N loss changes dramatically.

     

Lignin degradation controls the production of dissolved organic matter in decomposing foliar litter

Lignin is considered to be a crucial component controlling litter decomposition but its role in the production of dissolved organic matter (DOM) from litter is not well understood. Our main objective therefore was to examine the amounts and properties of DOM produced in decomposing litter, with special emphasis on the role of lignin degradation. We exposed litter of five different tree species (Sycamore maple, Mountain ash, European beech, Norway spruce, Scots pine) in litterbags at the soil surface of two neighbouring sites to degradation under field conditions. Litterbags were sampled eight times during 27 months of exposure in the field. We determined mass loss and characterized the lignin fraction by two different methods (van Soest procedure, acid‐detergent lignin: ADL, CuO oxidation). Litter was irrigated in the laboratory and leachates were analysed for dissolved organic carbon (DOC) and characterized by UV and fluorescence spectroscopy. Litter decomposition followed a two‐stage model characterized by initially rapid and then decreasing degradation with time. In the initial phase of litter decomposition, leached amounts of DOM decreased with time and no effects of lignin degradation were found. The contents of ADL in the litter residues and CuO oxidation products suggest larger degradation and oxidation of lignin in beech, spruce and pine litter than in maple and ash litter. The production of DOM from litter with larger lignin degradation increased in the second phase of decomposition, when mass loss exceeded 10–20%. In contrast, DOM produced from litter showing weak lignin degradation (maple, ash) did not increase further in the second phase of decomposition. In the leachates of litter with large lignin degradation (beech, spruce, pine), UV absorbance and fluorescence spectroscopy indicated a larger increase in the contribution of lignin‐derived compounds to DOM with increasing mass loss than for litter species with relatively stable lignin. We conclude that degradation of lignin is an important control on DOM production during the second phase of litter decomposition.     

Effect of N addition,moisture, and temperature on soil microbial respiration and microbial biomass in forest soil at different stages of litter decomposition

Purpose

The objective of the present study was to investigate the interactive effects of nitrogen (N) addition, temperature, and moisture on soil microbial respiration, microbial biomass, and metabolic quotient (qCO₂) at different decomposition stages of different tree leaf litters.

Materials and methods

A laboratory incubation experiment with and without litter addition was conducted for 80 days at two temperatures (15 and 25 °C), two wetting intensities (35 and 50 % water-filled porosity space (WFPS)) and two doses of N addition (0 and 4.5 g N m^?2, as NH₄NO₃). The tree leaf litters included three types of broadleaf litters, a needle litter, and a mixed litter of them. Soil microbial respiration, microbial biomass, and qCO₂ along with other soil properties were measured at two decomposition stages of tree leaf litters.

Results and discussion

The increase in soil cumulative carbon dioxide (CO₂) flux and microbial biomass during the incubation depended on types of tree leaf litters, N addition, and hydrothermal conditions. Soil microbial biomass carbon (C) and N and qCO₂ were significantly greater in all litter-amended than in non-amended soils. However, the difference in the qCO₂ became smaller during the late period of incubation, especially at 25 °C. The interactive effect of temperature with soil moisture and N addition was significant for affecting the cumulative litter-derived CO₂-C flux at the early and late stages of litter decomposition. Furthermore, the interactive effect of soil moisture and N addition was significant for affecting the cumulative CO₂ flux at the late stage of litter decomposition but not early in the experiment.

Conclusions

This present study indicated that the effects of addition of N and hydrothermal conditions on soil microbial respiration, qCO₂, and concentrations of labile C and N depended on types of tree leaf litters and the development of litter decomposition. The results highlight the importance of N availability and hydrothermal conditions in interactively regulating soil microbial respiration and microbial C utilization during litter decomposition under forest ecosystems.

     

Effects of organic chemical quality and mineral nitrogen addition on lignin and holocellulose decomposition of beech leaf litter by Xylaria sp.

Mycobiota and chemical composition of bleached and non-bleached portions were studied on leaf litter of beech (Fagus crenata Blume). By surface sterilization method, two xylariaceous species Xylaria sp. and Geniculosporium sp.1 were dominantly isolated in both portions. Frequency of occurrence of Xylaria sp. was significantly higher in the bleached portion than in the non-bleached portion. In the bleached portion, lignin concentration was lower than in the non-bleached portion, indicating that Xylaria sp. and Geniculosporium sp.1 took part in lignocellulose decomposition in the study site. Effects of organic chemical quality of litters and exogenous mineral nitrogen (NH₄ and NO₃) addition were then investigated on in vitro lignin decomposition by Xylaria sp. Weight loss of lignin was significantly related to lignocellulose index (LCI) for four litter types tested. In NH₄ and NO₃ addition treatments, lignin decomposition was completely and partially suppressed, respectively. Xylaria sp. produced bleaching spots on beech leaf litter in vitro in which lignin concentration was lower than in the non-bleached portion. These results suggest that heterogeneous distribution of carbon and nitrogen resources may control lignin decomposition on the litter by the fungus.     

Veränderungen in der stofflichen Zusammensetzung von Buchenstreu und Gerstenstroh beim Abbau unter Laborbedingungen

Chemical changes of beech litter and barley straw during decomposition under laboratory conditions Beech litter and barley straw were incubated at 20°C and 70% of maximum water holding capacity in the presence and absence of artificial “soil” and earthworms (Eisenia fetida). Results show that beech litter biodegradation was enhanced by E. fetida during the first part, but delayed in later stages of the incubation period, as indicated by the changes of ash contents and C-to-N ratios with progressive decomposition. In the long run the organic matter (OM) of beech litter tended to be stabilised through the action of worms. In contrast, for barley straw a more intense biodegradation was observed in the presence of E. fetida throughout the experiment. Almost 80% of litter and straw OM could be identified by means of wet chemical degradation methods (70% polysaccharides, lignin; 10% lipids, protein). The proportion of the exclusively plant-derived constituents cellulose and lignin showed a partly strong decrease with progressive decomposition; simultaneously the contents of also microbially synthesised components such as non-cellulosic polysaccharides and protein increased. Changes of the non-cellulosic polysaccharide-cellulose-quotients (NCQ), lignin-cellulose-quotients (LCQ), and acid-to-aldehyde ratios (ac/al)_v and (ac/al)_s in the residual lignin reflected well the litter decomposition process. At the end of the experiment - irrespective of treatments - the degree of beech litter biodegradation was comparable to that of Of-Oh transitional layers in beech-derived forest humus profiles. In the case of barley straw only NCQ and LCQ, but not (ac/al)_v,s were valuable parameters for the characterisation of the decomposition process.     

Influence of elevated UV-B radiation on leaf litter chemistry and subsequent decomposition in humid subtropical China

Purpose

Exposure to elevated ultraviolet B (UV-B) radiation during plant growth may influence plant tissue chemistry and subsequent decomposition. We conducted a 22-month decomposition experiment to evaluate the effects of UV-B radiation on litter chemistry and subsequent decomposition in humid subtropical forest systems.

Materials and methods

Leaf litters were derived from five native tree species, including Cunninghamia lanceolata, Cinnamomum camphora, Schima superba, Cyclobalanopsis glauca, and Elaeocarpus sylvestris, which grew under ambient and elevated UV-B radiation treatments for 1 year.

Result and discussion

UV-B treatment significantly altered the original C, N, P, K, and lignin content and ratios of C/N, lignin/N, and C/P of leaf litter of five species but just slightly accelerated decomposition at variable degree from 2 % to 13 %. Statistical analyses showed litter species, but not UV-B treatment, had significant effect on decomposition. Only initial lignin content was significantly related to the decay rate. Abundant precipitation and warm temperature in subtropical China maybe weaken or even mask the importance of litter chemistry change resulted from UV-B radiation to decomposition especially in early decomposition stage.

Conclusions

Exposure to supplemental UV-B level induced significant changes of the initial leaf litter chemistry but did not accelerate significantly subsequent decomposition of each species in humid subtropical areas of China at least in the early phase. The interspecific differences in litter chemistry of the five species showed greater effect on decomposition than elevated UV-B radiation at the early decomposition stage.     

Effects of fungal inocula on the decomposition of lignin and structural polysaccharides in Pinus sylvestris litter

 Litter bags containing sterile Scots pine (Pinus sylvestris) needles (19.8% lignin, 26.5% cellulose and 0.34% N) were inoculated with two species of fungi in the laboratory and then placed in the litter layer of a pine plantation. Marasmius androsaceus, which can degrade lignocellulose, was initially displaced by other fungal colonisers and was not detected in the litter after 2–3 months; but was re-isolated from the needles after 12 months. Trichoderma viride, which is a cellulolytic species and also antagonistic to other fungi, dominated the litter throughout the experiment. The control litter was naturally colonised by litter fungi. After 12 months, mass losses were similar at 52% for M. androsaceus and 48% for T. viride, compared with 36% for the control litter colonised by a more complex fungal community. Lignin concentrations increased with time in control litter and with T. viride because mass losses of carbohydrates were greater than those of lignin. Litter inoculated with M. androsaceus showed significant lignin decomposition throughout the experiment but cellulose concentrations showed a proportional increase in the first 6 months, suggesting that the fungus was preferentially exploiting hemicellulose and non-structural carbohydrates. Analysis of TFA-extractable sugars (mainly from hemicellulose) and CuO-derived phenylpropanoid moieties from lignin confirmed the differential patterns of resource decomposition which were not evident from total mass losses. During the initial stages of decomposition, T. viride was as effective in utilising structural polysaccharides as the complex fungal community in the control litter. Furthermore, M. androsaceus not only exhibited unexpectedly low cellulolytic activity but also facilitated lignin depolymerisation after the fungus was no longer detectable in the litter. The pre-inoculation of litter with these two fungal species therefore affected the overall dynamics of decomposition at a biochemical level. This study illustrates the importance of understanding the effects and interactions of specific fungi, rather than assumptions about the functional competence of diverse communities, on the processes of litter decomposition. Received: 5 July 2000     

Rates of decomposition and nutrient mineralization of leaf litter from different orchards under hot and dry sub-humid climate

Leaf litter decomposition is a critical step in nutrient cycling and providing nutrients to plants. Decomposition of dry matter, lignin, ligno-cellulose, cellulose and polyphenols was investigated in relation to nitrogen (N), phosphorus (P) and potassium (K) dynamics in leaf litter of mango, guava and litchi orchards under hot and dry sub-humid climate. Leaf litter of mango and guava decomposed more rapidly than that of litchi with decay constants of 3.22, 1.33 and 0.62 yr^-1, respectively. The leaf litter organic substances like polyphenol lost more rapidly followed by cellulose, lignin and ligno-cellulose throughout the period of decomposition. The N was released faster both in mango and guava with decay constant of 4.06 and 2.11 yr^-1, respectively. The release of K was faster in mango followed by guava and litchi with decay constant of 4.66, 3.18 and 1.63 yr^-1, respectively. The leaf litter decomposition was significantly positively correlated with soil fungal and bacterial biomass, rainfall and air temperature, while the leaf chemistry showed significant negative correlations in all the orchards. The results demonstrated that mango leaf litter was found to be the best followed by guava, and litchi in terms of N, P, and K return in less period of time.     

A litter-slurry technique elucidates the key role of enzyme production and microbial dynamics in temperature sensitivity of organic matter decomposition

The rate at which organic matter decomposes generally increases with temperature, unless it is physico-chemically protected from enzymatic depolymerization. The temperature sensitivity of decomposition should increase with decreasing reaction rates, corresponding to increasing activation energy of the decomposing compounds. One approach to testing this carbon-quality temperature hypothesis is to study the effect of temperature on leaf litter decomposition, because fresh surface litter is unprotected. However, other factors such as humidity co-vary with temperature, and biological processes such as enzyme production and microbial population growth may also be thermally sensitive. We developed a litter slurry approach to isolate the effect of temperature and litter quality on decomposition. We found that pine litter decomposed faster than oak litter, consistent with a lower C:N and lignin:N ratio. During the first 14 days of decomposition, there was no difference in decomposition rate for litter incubated at 25 °C compared to 35 °C. Lower potential enzyme activity at 35 °C suggested that enzyme production was suppressed at 35 °C compared to 25 °C, resulting in similar in situ enzyme activities at the two temperatures. After 14 days, enzyme pools were similar between the two incubation temperatures, which resulted in faster decomposition at the warmer temperature, consistent with enzyme kinetic theory. At Day 14, the decomposition rate of the high quality pine litter was more temperature sensitive than the decomposition rate of the lower quality oak litter, suggesting that the quality of soluble pool rather than bulk chemistry determined the temperature sensitivity during this stage. After 28 days of incubation, oak litter decomposition was more temperature sensitive than pine litter, consistent with the carbon temperature-quality hypothesis. The litter slurry approach revealed that biological responses to temperature can affect the apparent temperature sensitivity of decomposition, and highlight a need for further research into microbial responses to temperature.     

甘肃省兴隆山森林主要树种凋落叶分解速率与初始质量的关系

[目的]开展凋落叶分解速率研究,探讨凋落叶分解速率与初始质量的关系,为甘肃省兴隆山森林生态系统物质循环研究提供依据。[方法]采用凋落物分解袋法,以兴隆山青杄、山杨和白桦3种主要树种的凋落叶为研究对象,进行凋落叶分解速率及凋落叶初始质量的研究,明确凋落叶分解速率与初始质量的关系。[结果]青杄中龄林针叶分解速率为0.16,95%分解期为19.08a;青杄近熟林针叶分解速率为0.13,95%分解期为23.70a;山杨和白桦凋落叶分解速率均为0.11,95%分解期分别为28.57a和27.27a;山杨和白桦凋落叶分解速率明显要小于青杄针叶,这很可能是凋落叶分解主场效应和分解袋孔径较小所致。凋落叶分解速率与氮含量呈显著线性正相关,与木质素含量、碳/氮值、木质素/氮值和钾含量呈显著线性负相关,特别是与木质素含量、氮含量和木质素/氮值,相关系数均达0.700 0以上;钾含量、木质素含量、木质素/氮、碳/磷和纤维素含量是影响兴隆山森林凋落叶分解速率的重要指标。[结论]木质素/氮值是影响凋落叶分解速率的关键质量指标,凋落叶初始木质素/氮值越高,分解速率越低。