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1.
Forest ecosystems in Taiwan are periodically influenced by typhoons that cause large amounts of litter input to the soil. The potential rapid decomposition of such litter under the warm and moist climatic conditions in Taiwan may lead to nutrient losses via seepage. The goal of this study was to investigate the dynamics of C, N, K, Ca, Mg, and dissolved organic carbon (DOC) during decomposition of Chamaecyparis obtusa var. formosana leaves in a field study at the Yuanyang Lake site in N Taiwan. We simulated the effect of a typhoon by adding about three times the annual aboveground litterfall (totally 13,900 kg ha–1) as fresh leaves. Litterbags were taken at 7 dates over 16 months, followed by detection of mass loss and element composition in the remaining litter. Aqueous extracts of the remaining litter were analyzed for DOC and major elements. The properties of DOC were characterized by fluorescence spectra and by its stability against microbial decomposition. The litter mass loss was 35% after 16 months. The losses of Ca after 16 months from the litter bags were about equivalent to mass loss (39%), while those of K and Mg reached 86% and 60% of the initial amount, respectively. From the 13,900 kg ha–1 of litter applied in total, 59 kg K ha–1 and 12 kg Mg ha–1 were released in the 16 months decomposition period, most of it in the first 4 months. The total release of Ca amounted to 69 kg ha–1 but was more evenly distributed throughout the 16 months of observation. The absolute amount of N in the decomposing litter increased by 37% while the C : N decreased from 69 to 34. Extrapolated to the manipulation treatment, this resulted in a N gain of 36 kg N ha–1 within 16 months. The leaching of K and DOC in laboratory extractions followed an asymptotic function with highest leaching from the initial litter and subsequent decrease with time of decomposition. On the contrary, the leaching of Ca and Mg reached a maximum after 2–4 months of incubation. About 2% of the C was extractable with water from the initially incubated leaves. The bioavailability of the extracted DOC decreased with litter age. Our results indicate that the decomposition of large amounts of litter induces a high risk of K and Mg losses with seepage, but the risk for N losses is low. The sources of N accumulation in decomposing litter at this site require further studies. In the initial phase of litter decomposition, the release of DOC seems to be an important contribution to mass loss.  相似文献   

2.
Abstract

In a southern boreal aspen forest located in Saskatchewan, Canada, we examined decomposition rates of leaf litter from trembling aspen (Populus tremuloides Michx.), hazel (Corylus cornuta March.), and a mixture of different species over a six‐month period. Mass loss was measured in the field using the litter bag method. The greatest mass losses occurred during the first month regardless of litter type. On average, mass loss during the first 28 days was 3.2 g#lbkg‐1#lbd‐1 for the aspen leaves, 4.4 for hazel leaves and 4.9 for the mixture. The initial rapid loss of weight is attributed to leaching and decomposition of water soluble material. The decomposition rates of the leaf litter were related to water‐soluble organic carbon and nitrogen content, and C:N ratio. Several models were used to describe mass loss of the aspen, hazel, and mixed leaf litter at the early stages of decomposition. A single model was not found to be appropriate to describe decomposition of all leaf‐litter types. A second order model provided the best fit for the aspen litter decomposition, while the logarithmic model best described the decomposition of hazel and mixed leaf litter.  相似文献   

3.
Forest management practices often generate clear-cut patches, which may be colonized by ants not present in the same densities in mature forests. In addition to the associated changes in abiotic conditions ants can initiate processes, which do not occur in old-growth stands. Here, we analyse the effects of ants and aphid honeydew on litter solution of Norway spruce, microbial enzyme activities, and needle decomposition in a field and greenhouse experiment during summer 2003. In the field, low ant densities had relatively little effects on litter solution 30 cm away from a tree trunk, but significantly increased organic carbon concentrations and decreased inorganic nitrogen concentrations next to a trunk where ants tend to build their nests. In a greenhouse experiment, the addition of ants to lysimeters containing spruce litter significantly increased dissolved organic carbon (DOC), dissolved organic nitrogen (DON), NH4-N, NO3-N and K concentrations in litter solutions compared to the control treatment, while the simulation of aphid infestation (addition of honeydew) significantly increased DOC as a direct result of honeydew leaching, and decreased inorganic N concentrations in leachates. The presence of ants resulted in a changed composition of dissolved organic matter (DOM) with more aromatic and complex compounds, and microbial enzyme activity was significantly higher in litter extracts from the ant treatment compared to the honeydew and control treatment. However, mass loss, litter %C and %N were not affected by ants or honeydew. Our results suggest that ants have a distinct and immediate effect on solution composition and microbial activity in the litter layer indicating accelerated litter decay whereas the effect of honeydew was insignificant.  相似文献   

4.
The objective of this study was to determine whether differences in canopy structure and litter composition affect soil characteristics and microbial activity in oak versus mixed fir-beech stands. Mean litter biomass was greater in mixed fir-beech stands (51.9t ha−1) compared to oak stands (15.7t ha−1). Canopy leaf area was also significantly larger in mixed stands (1.96m2 m−2) than in oak stands (1.73m2 m−2). Soil organic carbon (C org) and moisture were greater in mixed fir-beech stands, probably as a result of increased cover. Soil microbial biomass carbon (C mic), nitrogen (N mic), and total soil nitrogen (N tot) increased slightly in the mixed stand, although this difference was not significant. Overall, mixed stands showed a higher mean C org/N tot ratio (22.73) compared to oak stands (16.39), indicating relatively low rate of carbon mineralization. In addition, the percentage of organic C present as C mic in the surface soil decreased from 3.17% in the oak stand to 2.26% in the mixed stand, suggesting that fir-beech litter may be less suitable as a microbial substrate than oak litter.  相似文献   

5.
We conducted a controlled experiment to evaluate Chinese-fir litter decomposition and its response to the addition of inorganic N. Litter-derived CO2, microbial biomass carbon (MBC), and dissolved organic carbon (DOC) were monitored during an 87-d incubation of a mixed soil–litter substrate using the 13C tracer technique. Litter C was mostly converted to CO2 (47.4% of original mass), followed by MBC (3.6%), and DOC (1.0%), with 48% remaining unaltered in the soil. The litter decomposition rate significantly increased with the addition of inorganic N, although the effect depended on whether N was added as NH4+ or NO3−. Soil-derived CO2, MBC, and DOC also increased following the combined addition of litter and N. The results showed that only a small percentage of litter C was retained as MBC or DOC and that the conversion rate depended, in part, on the form of inorganic N added to the Chinese-fir plantation soil.  相似文献   

6.
Leaves lying on the forest floor are a major source of dissolved organic substances in soil and surface waters, and these substances have important effects in those environments. We used zero‐tension lysimeters to study the chemical characteristics of water percolating through litter from various species of forest trees. The leaching rates were greatest in the autumn and declined rapidly thereafter, especially for deciduous litter. During an annual cycle, 2.5–17% of the initial contents of the carbon in the litter was recovered as dissolved organic carbon in percolates. Humus‐like substances, hydrophilic acids and hydrophilic neutral compounds constituted the major fractions of dissolved C. Leachates from deciduous leaf litter were only partly biodegradable, and those from spruce needles were scarcely biodegradable. Low molecular weight organic acids constituted 0–12% of the dissolved organic carbon in the percolates of the first autumn sampling and decreased over time. Acetic and formic acids were present at the largest concentrations, up to 30 μmol l?1 per g litter, and gluconic, pyruvic, fumaric, oxalic and citric acids were also frequent in significant concentrations. Among the aromatic acids, p‐hydroxybenzoic acid was identified in four out of five autumn samples. The organic components in litter leachates are important for the microbial activity in soil and surface waters. The organic acids enhance weathering and translocation of metals by their ability to form complexes. Litter is also a source of inorganic ions in soil solutions. The dominant cations in the percolates were K+, Ca2+ and Mg2+, and spruce litter also yielded large quantities of Al and Fe.  相似文献   

7.
The effects of soil mesofauna and different farming systems on decomposition of clover (Trifolium repens) litter were investigated in a laboratory experiment. Microcosms were incubated for 16 weeks with fine and coarse litterbags in soils from three types of management systems: fallow, integrated farming and organic farming, the latter two cropped with wheat. The effects were studied by analysing litter mass loss, C and N content, DOC, nitrate and pH in soil leachate, and CO2 production, as well as mesofauna. Mesofauna significantly accelerated mass loss and C and N release from clover litter in all three soils. With mesofauna access, at the end of the experiment average clover mass loss was almost twice as high and clover C and N content were 60% lower than without mesofauna. Farming systems influenced the decomposition through affecting both element turnover and mesofauna. Although in the first weeks less N was leached from organic farming than from integrated farming soil, cumulative N leaching did not differ between these soils. However, more than 20% less N was leached from the fallow soil than from the field soils. CO2 production was highest in fallow soil. Here, mesofauna had no effect on this variable. In soil with integrated farming, mesofauna reduced cumulative CO2 production by 10% whereas in soil from organic farming it increased CO2 production by 20%. Our data suggest that differences in C and N turnover in different management systems are strongly mediated by soil mesofauna.  相似文献   

8.
The relative contributions of litter and humified organic matter as the source of dissolved organic carbon (DOC) leached from organic layers of forest soils are poorly understood. In the present investigation, 13C labelled spruce litter was used to study the role of recent litter in the leaching of DOC from a coniferous forest floor in southern Sweden, while litterbags were used to quantify the total loss of C from the labelled litter. The labelled litter applied on bare lysimeters released considerable amounts of DOC during the first weeks, but the concentration of DOC originating from labelled litter decreased gradually from 176 mg litre−1 during the first sampling period in May to 5 mg litre−1 in the last sampling period in October. Only a moderate flush of DOC from the labelled litter occurred under the Oe and Oa horizons, with concentrations of 20 and 6 mg litre−1 from labelled litter, equal to 19 and 9% of the total DOC flux, respectively, during the first sampling period. Total flux of DOC from labelled litter from May to September was 16 g m−2, whereas only 2.2 and 0.9 g m−2 were captured under the Oe and Oa horizons, respectively. The almost complete loss of new DOC implies that DOC leached from the Oe and Oa horizons consists not of recent litter‐derived carbon, but of DOC produced in these two horizons themselves. Water‐extractable organic carbon from labelled litter left in litterbags in the field for 4 months consisted of about one‐third native carbon from external sources at the experimental site and two‐thirds of the labelled litter. In contrast, the 13C content of the bulk litter from the litterbags was not changed by the incubation in the field. We suggest that the soluble native carbon in water extracts originated from throughfall DOC that had been assimilated by microorganisms in the litterbags.  相似文献   

9.
In this study, we describe the seasonal variation in 13C abundance in the litter of two Sphagnum species and four vascular plant species during 3 years of field decomposition in an Italian alpine bog. Litter bags were periodically retrieved at the end of summer and winter periods, and the δ13C in residual litter was related to mass loss, litter chemistry, and climatic conditions. In Sphagnum litter, higher rates of decomposition during summer months were associated with an increase of δ13C probably due to the incorporation of microbial organic compounds rich in 13C in the residual litter. In the litter of Eriophorum vaginatum, Carex rostrata and Calluna vulgaris, we observed a decrease of δ13C with an increase in the concentration of lignin-like compounds. The residual litter of Potentilla erecta showed a decrease of 13C abundance during the first 2 years, but on proceeding the decomposition, the δ13C increased again probably reflecting the incorporation of microbial organic compounds.  相似文献   

10.
The relative contributions of sources of carbon in soils, such as throughfall, litter, roots, microbial decay products and stable organic fractions, to dissolved organic C are controversial. To identify the origin of dissolved organic C, we made use of a 4‐year experiment where spruce and beech, growing on an acidic loam and on a calcareous sand, were exposed to increased CO2 that was depleted in 13C. We traced the new C inputs from trees into dissolved organic C, into water‐extractable organic C, and into several particle‐size fractions. In addition, we incubated the labelled soils for 1 year and measured the production of dissolved organic C and CO2 from new and old soil C. In the soil solutions of the topsoil, the dissolved organic C contained only 5–10% new C from the trees. The δ13C values of dissolved organic C resembled those of C pools smaller than 50 µm, which strongly suggests that the major source of dissolved organic C was humified old C. Apparently, throughfall, fresh litter and roots made only minor contributions to dissolved organic C. Water‐extractable organic C contained significantly larger fractions of new C than did the natural dissolved organic C (25–30%). The δ13C values of the water‐extractable organic C were closely correlated with those of sand fractions, which consisted of little decomposed organic carbon. The different origin of dissolved and water‐extractable organic C was also reflected in a significantly larger molar UV absorptivity and a smaller natural 13C abundance of dissolved organic C. This implies that the sampling method strongly influences the characteristics and sources of dissolved organic C. Incubation of soils showed that new soil C was preferentially respired as CO2 and only a small fraction of new C was leached as dissolved organic C. Our results suggest that dissolved organic C is produced during incomplete decomposition of recalcitrant native C in the soils, whereas easily degradable new components are rapidly consumed by microbes and thus make only a minor contribution to the dissolved C fraction.  相似文献   

11.
Summary The functional roles of the fungivorous collembolan Tomocerus minor and the detritivorous isopod Philoscia muscorum during the decomposition of Pinus nigra needles were studied in mesocosms filled with two different types of F1 litter, obtained from two different forest soils. The effects of the animals on the availability of K+, Ca2+, NO inf3 sup- , NH inf4 sup+ , and PO inf4 sup3- and on the respiration, dehydrogenase, and cellulase activity of microorganisms were measured over one growing season. The animals were introduced into the F1 litter in three densities. The most important animal effect was a buffering effect, in that addition of the animals increased nutrient availability and microbial activity where the corresponding values in control mesocosms without animals were low, and decreased the nutrient availability and microbial activity where control values were high. This effect occurred for both species and was most evident in the substrate with the highest temporal fluctuations. The effects on nutrient availability are attributed to an animal effect on the activity of and successional stage reached the microbial community, with NH inf4 sup+ availability seen as the most important factor. The concept of functional groups in relation to these animal effects is discussed.  相似文献   

12.
Dissolved organic matter (DOM) plays an important role in transport, storage and cycling of carbon (C) and nitrogen (N) in forest soils where litter is one of the main sources. The aim was to study the amount and characteristics of DOM leached from freshly fallen litters of silver birch (Betula pendula Roth.), Norway spruce (Picea abies (L.) Karst.) and their mixture during decomposition. DOM was collected after irrigation on eight occasions during 252 days incubation in the laboratory at about 18°C, including one freeze‐thaw cycle. During the incubation about 33–35% of C from birch and spruce litter and 40% of C from their mixture was lost. The total cumulative flux of dissolved organic carbon (DOC) from the mixture of litters was approximately 40% larger than that from single litters. The flux of DOC, DON, phenolic compounds and proteins followed a two‐stage pattern during decomposition. In the first stage the initially large fluxes decreased gradually. In the second stage, after freezing and thawing, the fluxes tended to increase again. Mixing birch and spruce litters and a freeze‐thaw cycle seems to increase the decomposition of litter and result in the increased flux of DOC, DON and phenolic compounds. The flux of hemicelluloses and the degradability of DOM were large at the first leaching occasion and decreased during the incubation. Birch had a 40% larger total flux of easily degradable DOM than spruce, supporting the previous consistent signs of greater microbial biomass and activities related to C and N cycling in soil under birch than under spruce. It is known that recalcitrant DOM might be stabilized whereas labile DOM may promote microbial activity and nutrient cycling. We conclude that the storage and cycling of C and N is affected by both tree species and degradation stage of litter in forest soils.  相似文献   

13.

Purpose

Little is known about the interactive effects of temperature, nitrogen (N) supply, litter quality, and decomposition time on the turnover of carbon (C) and N of forest litter. The objective of this study was to investigate the interactive effects of warming, N addition and tree species on the turnover of C and N during the early decomposition stage of litters in a temperate forest.

Materials and methods

A 12-week laboratory incubation experiment was carried out. The leaf litters including two types of broadleaf litters (Quercus mongolica and Tilia amurensis), a needle litter (Pinus koraiensis), and a mixed litter of them were collected from a broad-leaved Korean pine mixed forest ecosystem in northeastern China in September 2009. Nine treatments were conducted using three temperatures (15, 25, and 35 °C) combined with three doses of N addition (equal to 0, 75, and 150 kg?·?ha?1?a?1, respectively, as NH4NO3).

Results and discussion

After 12 weeks of incubation, the mass loss ranged between 12 and 35 %. The broadleaf litters had greater mass loss and cumulative CO2–C emission than the needle litter. Temperature and N availability interacted to affect litter mass loss and decomposition rate. The dissolved organic carbon (DOC) and nitrogen (DON) concentrations in litter leachate varied widely with litter types. DOC increased significantly with increased temperature but decreased significantly with increased N availability. DON increased significantly with increased N availability but showed a higher level at the moderate decomposition temperature. The amounts of CO2 and N2O emission were significantly higher at 25 °C than those at 15 and 35 °C, and were significantly increased by the N addition.

Conclusions

The present study indicated relatively intricate temperature and N addition effects on C and N cycling during early stages of litter decomposition, implying that future increases in temperature and N deposition will directly affect C and N cycling in broad-leaved Korean pine mixed forest ecosystem, and may indirectly influence the ecosystem composition, productivity, and functioning in NE China. It is, therefore, important to understand the interactive effects of biotic and abiotic factors on litter decomposition in field conditions in order to assess and predict future ecosystem responses to environmental changes in NE China.  相似文献   

14.
It is widely accepted that microarthropods influence decomposition dynamics but we know relatively little about their effects on litter chemistry, extracellular enzyme activities, and other finer-scale decomposition processes. Further, few studies have investigated the role of individual microarthropod species in litter decomposition. The oribatid mite Scheloribates moestus Banks (Acari: Oribatida) is abundant in many U.S. ecosystems. We examined the potential effects of S. moestus on litter decomposition dynamics and chemical transformations, and whether these effects are influenced by variation in initial litter quality. We collected corn and oak litter from habitats with large populations of S. moestus and in microcosms with and without mites measured respiration rates, nitrogen availability, enzyme activities, and molecular-scale changes in litter chemistry. Mites stimulated extracellular enzyme activities, enhanced microbial respiration rates by 19% in corn litter and 17% in oak litter over 62 days, and increased water-extractable organic C and N. Mites decreased the relative abundance of polysaccharides in decomposing corn litter but had no effect on oak litter chemistry, suggesting that the effects of S. moestus on litter chemistry are constrained by initial litter quality. We also compared the chemistry of mite feces to unprocessed corn litter and found that feces had a higher relative abundance of polysaccharides and phenols and a lower relative abundance of lignin. Our study establishes that S. moestus substantially changes litter chemistry during decomposition, but specific effects vary with initial litter quality. These chemical transformations, coupled with other observed changes in decomposition rates and nutrient cycling, indicate that S. moestus could play a key role in soil C cycling dynamics.  相似文献   

15.
Summary A laboratory incubation experiment was carried out over 17 weeks to determine the effect of liming on soil organic matter. The amount of lime as calcium hydroxide [Ca(OH)2] required to completely neutralise exchangeable Al was found to be five times the standard lime requirement. This large amount of lime had a limited overall effect on the short-term stability of soil organic matter, causing the release of 1300 g g-1 of C (1.7% total soil C) above the control during the incubation. Liming may have altered the potential availability of soil organic matter and organic P, as shown by a marked reduction in the extractability of soil organic P with sodium bicarbonate and sodium hydroxide. The latter was unlikely to be due to the formation of calclium-P artefacts, and may be attributed to the combined chemical effects of added calcium hydroxide and precipitation of exchangeable Al on the nature and solubility of soil organic constituents and organomineral complexes. The addition of lime increased the degradation of added oak leaf litter by 50%, from 3.2 to 4.7 mg g-1, as determined by CO2 evolution. The enhanced litter degradation indicated increased microbial activity in limed soil, but this improvement had only minor effects on the stability of native organic matter. This study highlights the need for further research into the relationships between the chemical nature of organic P in soil and the physical, chemical, temporal, and agronomic factors that control its turnover and availability.  相似文献   

16.
Summary The effect of diverse soil fauna (Collembola, Acari, Enchytraeidae, Nematoda) on decomposition of dead organic matter was studied in microcosms containing (1) birch leaf litter, (2) raw humus of coniferous forest and (3) litter on humus. Total respiration (CO2 evolution) was monitored weekly, and mass loss, length of fungal hyphae (total and metabolically active) and survival of animal populations were checked at the end of weeks 12 and 21–22 from the start of experiment. Animal populations established themselves well during the incubation. At the end of the experiment some replicates containing litter had microarthropod densities of up to 500 specimens per microcosm, corresponding to a field population of 200 000 m–2. The soil animals had a positive influence on total respiration in all substrates. By the end of experiment 32.0%, 22.6% and 14.6% more CO2 had evolved in the presence of animals in litter, litter + humus and humus alone, respectively. There was clear trend towards a higher mass loss in the presence of animals, though it was significant in litter only. Our results showed that a diverse soil animal community enhances the activity of soil microbes, and may thereby accelerate decomposition in raw coniferous forest soil.  相似文献   

17.
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.  相似文献   

18.
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].  相似文献   

19.
The decomposition and nutrient content of litter was studied for 2 years in regrowth Eucalyptus diversicolor forest to which N (0, 200 kg ha-1 year-1) and P (0, 30, 200 kg ha-1) had been applied. The P addition increased, and the N addition decreased, the rate of dry weight loss of decomposing litter. Analysis of the coefficients of a double exponential decay model with components describing the release of labile and resistant fractions indicated that decomposition of the resistant component of litter was most affected by the fertilizer additions. Treatment with N reduced the rate of loss of this component and increased its half-life by approximately 30%, whereas P treatment increased its rate of decay and decreased its half-life by approximately 30%. P accumulated in litter during decomposition. P uptake and retention was greater in P-treated than untreated plots. The application of N reduced P accumulation in litter. An accumulation of N also occurred during decomposition, the amount of N imported into litter being greater on plots treated with N fertilizer. Treatment with N affected the amount of S in decomposing litter. Litter on N-treated plots either accumulated more S or released it more slowly than litter on plots not treated with N. The application of N as NH4NO3 decreased forest-floor litter pH, increased litter layer mass (by 15%), and increased the amount of N (by 34%) and S (by 32%) stored in the forest floor. Treatment with P reduced the amount of N (by 22%) stored in the litter layer. The application of 200 kg P ha-1 in the absence of N increased the store of P in the litter layer by 80%, but when N and P were applied together the amount of P in the litter was not significantly different between P treatments.  相似文献   

20.
 In microcosm experiments Porcellio scaber increased litter disappearance of oak and alder litter. Alder litter disappeared at more than twice the rate of oak litter. Soil texture did not influence the disappearance of oak litter; however, disappearance of alder litter was enhanced on silt rather than on sand. P. scaber enhanced microbial communities (i.e. microbial respiration and microbial biomass) on both silt and sand when feeding on either alder or oak. Overall, microbial respiration increased 10-fold when isopods fed on oak litter on sand and 20-fold when isopods fed on alder litter on sand. On silt, the initially high microbial respiration remained constant when isopods fed on oak and doubled when they fed on alder litter. In all treatments without P. scaber there was a decrease in microbial respiration over the 12-week experimental period. The availability of macronutrients (Corg, Ntot, P, K, Mg, Ca) in the topsoil was increased when P. scaber fed on alder litter but less pronounced when P. scaber fed on oak litter. Using sand as a substrate, there was an apparent increase only for Corg, Mg and Ca; on silt, increases in Corg, Ntot and P were measured. Under field conditions the contribution of P. scaber to nutrient fluxes will be higher on sand than on silt. Received: 1 July 1999  相似文献   

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