Litter Decomposition Studies Research Articles

Litter production and decomposition in the forested areas of traditional homegardens: a case study from Barak Valley, Assam, northeast India

Homegardens are one of the oldest forms of managed land use systems characterised by high diversity and complexity of their species structure which in turn contribute to efficient nutrient cycling. Litterfall and decomposition are the two major processes that replenish the soil nutrient pools and endow sustainability to these agroforests. A study was carried out in the village Dargakona, Barak Valley, northeast India to understand the pattern of litter production and litter decomposition in the traditional homegardens. Annual litter production was 6.27 Mg ha−1 with a bimodal distribution pattern and the nitrogen input through litterfall accounted for 48.17 kg ha−1 year−1. Litter decomposition studies for ten multipurpose trees revealed Sapium baccatum and Toona ciliata to be the most labile litter species and the decay rate coefficients varied among the species with differing rates of nutrient release pattern. Such studies can provide information regarding the litter quality of indigenous tree species and help validate farmers planting and management of multiple species which allows for efficient nutrient cycling of the system.

Litter decomposition of Brachiaria decumbens Stapf. and Calopogonium mucunoides Desv. in the rumen and in the field: a comparative analysis

Litter deposition and decomposition are important components of the nutrient cycling process in grasslands. Litter decomposition studies in the field are tedious and time-consuming. Finding an approach to speeding up research would therefore be a major advancement in the field. In this study, a comparative analysis of the litter decomposition process of signal grass (Brachiaria decumbens Stapf.) and calopo (Calopogonium mucunoides Desv.) in two distinct environments (field vs. goat rumen) was carried out. Two incubation trials were performed. In the first trial litter of both plant species was incubated in the rumen of fistulated goats using the in situ technique. Second trial, litter samples were incubated on signal grass pastures using the litter bag technique. Litter samples of signal grass and calopo were incubated by different periods in the rumen (0, 6, 12, 24, 48, 96, and 144 h) and in the field (0, 4, 8, 16, 32, 64, 128, and 256 days). At the end of the incubation period, the remaining biomass of signal grass was similar between rumen and field (~38%), but calopo decomposed more extensively in the field. The C:N ratio was considered high for signal grass (~100) at the beginning of the experimental period. Calopo showed initial C:N ratio of 29. Nitrogen was more extensively decomposed in the rumen as opposed to the field; however, despite several differences in terms of environment and time of incubation, remaining biomass at the end of incubation was similar between rumen and field trials, suggesting common limits for decomposition in both environments. Decomposition models, however, showed different relative decomposition rates (k) along the incubation period. As a result, the use of the rumen model to simulate field decomposition cannot be recommended.

Influence of soil organisms on accuracy predicting leaf litter decomposition by near infrared spectroscopy

To use Near Infrared Spectroscopy (NIRS) in the study of litter decomposition in field conditions, it's essential to know the relative role of different environmental factors that may affect its accuracy. This study attempts to determine the effects of soil organisms on direct predicting by NIRS, the stage of litter decomposition, expressed as the percentage of ash-free litter mass remaining (LMR). An experiment was carried out on 10 species and at different stages of litter decomposition produced by laboratory incubations. The LMR calibration was carried out on about two third of the set (267) of samples of the 10 species including grasses, shrubs, deciduous trees and evergreen trees. The standard error of calibration was 2.81. Predictions were carried out on the remaining third of the set of the samples and on samples of other species (Aleppo pine, beech, downy oak, holm oak and sweet chestnut) decomposed in laboratory in the same previous experimental conditions. The standard error of prediction varied between 2.93 and 3.41, with similar coefficients of determination (r2) of 0.94. The calibration equation obtained from the laboratory samples, was applied to samples of four species (Aleppo pine, downy oak, holm oak and sweet chestnut) that had decomposed in litter-bags on four sites (Cambo, Liouc, Montpellier and Pech-Rouge). The standard error of prediction was of 7.29, with r2 of 0.82 and a bias of -2.59. This precision, although lower than that obtained with laboratory samples, permits the use of NIRS in studies of litter decomposition in order to complete the classical methods. The role of earthworms and that of micro-organisms are also discussed. Keywords: NIRS, Litter decomposition, Earthworms, Mediterranean plant speciesCaJEB Vol. 3 (2) 2007: pp. 88-96

Changes in litter properties during decomposition: A study by differential thermogravimetry and scanning calorimetry

To verify the paradigm that organic matter (OM) quality ( q) decreases with decomposition it is necessary to define q in strictly chemical, operational terms. We suggest defining q as the result of a balance between the energy stored in OM and the external supply of energy needed to release it. We apply this concept to the study of litter decomposition in four European pine forests: boreal, cool Atlantic, Mediterranean and warm Atlantic. Intact litter cores were taken and transported to the laboratory, where needles were sorted into six classes that summarize the main facts of the decomposition: melanisation, fragmentation and perforation by mesofauna. Each class was analyzed by both differential thermogravimetry and differential scanning calorimetry to obtain its spectra of weight loss and energy release. In the non-decomposed needles, two peaks of weight loss and energy release appear: a labile peak at about 350 °C, and a recalcitrant peak at about 450 °C. During decomposition, both peaks (but especially the recalcitrant one) move to lower temperatures, and their shapes change from well defined to flattened. In Mediterranean litters, a third peak appears at about 500 °C, due probably to refractory products of neoformation. There is a continuous increase in the energy stored in the remaining litter (in Joules per unit OM): this increase is concentrated in both the most thermolabile fractions (lost at temperatures <350 °C) and the most thermostable ones (>450 °C). With decomposition OM becomes more recalcitrant (i.e., it is lost at higher temperatures), but its stored energy becomes more available (i.e., it is released at lower temperatures). Overall, the energetic benefit/cost ratio increases. Thus, our results to date do not agree with the current paradigm that q decreases with decomposition; rather, they suggest that, at least in the first phases we studied, q is maintained or even increases.

Limited evidence that mixing leaf litter accelerates decomposition or increases diversity of decomposers in streams of eastern Canada

Most studies of terrestrial litter decomposition in streams and rivers have used leaves from a single tree species, but leaf packs in streams in eastern North America are usually mixtures of two or more species. Litter mixtures may decay more quickly than either of the component species. If so, estimates of stream energy and nutrient budgets may be inaccurate. In northern Nova Scotia, Canada, we measured mass loss from binary mixtures (1:1 mass ratio) of leaf litter in mesh bags, using freshly fallen or air-dried litter from five species of canopy trees. We repeated the experiment eight times, in summer and fall, in two streams and a small river, over 3 years. In some trials we enumerated benthic invertebrate and fungal colonization of decaying litter. Although there were marked differences in mass loss rates among litter types, decomposition was accelerated in mixtures relative to the mean of the component species in only three of eight trials, and only in mixtures containing N-rich speckled alder leaves. Mixing yellow birch and red maple leaves inhibited decomposition. Diversity (Shannon–Weaver Index), species richness, and abundance of aquatic hyphomycete fungi, as indexed by conidial production, were never greater (and sometimes less) on litter mixtures than on the component species. Total numbers, taxonomic richness and diversity of benthic invertebrates generally, and litter-feeding species in particular, were not augmented by mixing litter types. Litter mixtures appear to dilute a preferred substrate with patches of a less preferred substrate. Our results provide only weak support for the contention that combining two litter types leads to acceleration of decomposition rates.

Plant litter decomposition in a semi-arid ecosystem controlled by photodegradation

The carbon balance in terrestrial ecosystems is determined by the difference between inputs from primary production and the return of carbon to the atmosphere through decomposition of organic matter. Our understanding of the factors that control carbon turnover in water-limited ecosystems is limited, however, as studies of litter decomposition have shown contradictory results and only a modest correlation with precipitation. Here we evaluate the influence of solar radiation, soil biotic activity and soil resource availability on litter decomposition in the semi-arid Patagonian steppe using the results of manipulative experiments carried out under ambient conditions of rainfall and temperature. We show that intercepted solar radiation was the only factor that had a significant effect on the decomposition of organic matter, with attenuation of ultraviolet-B and total radiation causing a 33 and 60 per cent reduction in decomposition, respectively. We conclude that photodegradation is a dominant control on above-ground litter decomposition in this semi-arid ecosystem. Losses through photochemical mineralization may represent a short-circuit in the carbon cycle, with a substantial fraction of carbon fixed in plant biomass being lost directly to the atmosphere without cycling through soil organic matter pools. Furthermore, future changes in radiation interception due to decreased cloudiness, increased stratospheric ozone depletion, or reduced vegetative cover may have a more significant effect on the carbon balance in these water-limited ecosystems than changes in temperature or precipitation.

Do rates of litter decomposition tell us anything we really need to know?

Results of several long-term studies of non-woody litter decomposition in forests indicate that we need to rethink why and how we measure rates of litter decomposition. Effects on litter decomposition rates were postulated to explain some of the nutritional effects of factors such as tree species, forest harvesting and fertilization. However, the accumulated experimental evidence indicates that litter decomposition rates do not mediate these responses. Many studies have reported litter mass loss becoming extremely slow at values considerably below 100%, indicating that early decay rates may not accurately foreshadow the entire decay process. Exclusion of soil faunal activities from current measurements of decomposition rates seriously reduces the likelihood that we are properly modeling decomposition. Finally, the use of regression and correlation analyses to determine which climate or initial litter quality factors control decay rate has led to many unwarranted and potentially misleading conclusions. These concerns are illustrated with examples from a suite of litter decomposition studies in British Columbia, Canada. Insights into nutrient cycling and carbon storage in ecosystems are more likely to arise from measuring the mass and nutrient content of annual litter input and determining the maximum decomposition limit and nutrient content at that stage, than by measuring early rates of decay. Improved predictions of relative decay rates of plant litters are likely to arise from a holistic approach based on plant life attributes rather than correlations based on individual initial litter chemistry parameters. Finally, a better understanding of the fate of faecal material of soil fauna is necessary before we can accurately predict and model litter decomposition.

Three new species of Hemienchytraeus (Enchytraeidae, Oligochaeta) from Amazonian forest soil

The species diversity of tropical enchytraeids is still largely unexplored, although knowledge of them is a desideratum regarding the potential of species‐related data as biological soil quality indicators. Here we describe three new species of the mainly terrestrial enchytraeid oligochaete genus Hemienchytraeus from a primary rain forest plot at the Brazilian Agroforestry Research Facility close to Manaus, Brazil (EMBRAPA‐CPAA: Empresa Brasileira de Pesquisa Agropecuária, Centro de Pesquisa Agroflorestal na Amazônia Ocidental). Hemienchytraeus siljae, H. patricii, and H. tanjae spp. nov. were discovered in a study of soil fauna and litter decomposition in the framework of a project series that was aimed at developing methods for sustainable land use in Amazonian rain forests (SHIFT ENV 52: Studies on Human Impact on Floodplains and Forests in the Tropics). The specimens were investigated alive and as stained whole mounts. The detailed descriptions cover almost the entire light‐microscopical anatomy of the animals, following results achieved with other enchytraeid genera where it has been demonstrated that taxonomical difficulties in Enchytraeidae can be overcome by more detailed descriptions. The three new species differ among each other in at least 16 different traits. Most notable are: (1) the size difference of chaetae in terminal and preclitellar segments; (2) the branching pattern of the oesophageal appendage; (3) the number and location of secondary pharyngeal gland lobes; (4) the number and location of preclitellar nephridia; and (5) the distribution pattern of clitellar gland cells, especially on the ventral side. About half of the differentiating characters are non‐sexual, which increases the possibility of identifying juvenile specimens to the species level—an important point for ecological studies. Most similar to H. siljae and H. patricii is H. stephensoni and most similar to H. tanjae is H. bifurcatus. The comparison of these species is made difficult by the poor original descriptions of H. bifurcatus and H. stephensoni and by an apparent overestimation of their intraspecific morphological variability in following accounts. Hemienchytraeus tanjae is distinguished from H. bifurcatus in coelomocyte size and texture, in the shape of the brain and in the absence of nephridial terminal vesicles. Furthermore, H. bifurcatus is considered as species inquirenda, due to the lack of important details in the original description and to the loss of type material. A literature‐based distinction of H. siljae and H. patricii from H. stephensoni remains inconclusive; type specimens of H. stephensoni (syntype specimens of the nominal species Enchytraeus cavicola, E. myrmecophilus and E. rangoonensis), however, differ clearly from H. siljae and H. patricii by a ventrally fully developed clitellum and by strongly thickened preclitellar septa, among other characters.

The Influence of Nutrient Availability on Soil Organic Matter Turnover Estimated by Incubations and Radiocarbon Modeling

We investigated the decomposability of soil organic matter (SOM) along a chronosequence of rainforest sites in Hawaii that form a natural fertility gradient and at two long-term fertilization experiments. To estimate turnover times and pool sizes of organic matter, we used two independent methods: (1) long-term incubations and (2) a three-box soil model constrained by radiocarbon measurements. Turnover times of slow-pool SOM (the intermediate pool between active and passive pools) calculated from incubations ranged from 6 to 20 y in the O horizon and were roughly half as fast in the A horizon. The radiocarbon-based model yielded a similar pattern but slower turnover times. The calculation of the 14C turnover times is sensitive to the lag time between photosynthesis and incorporation of organic C into SOM in a given horizon. By either method, turnover times at the different sites varied two- or threefold in soils with the same climate and vegetation community. Turnover times were fastest at the sites of highest soil fertility and were correlated with litter decay rates and primary productivity. However, experimental fertilization at the two least-fertile sites had only a small and inconsistent effect on turnover, with N slowing turnover and P slightly speeding it at one site. These results support studies of litter decomposition in suggesting that while plant productivity can respond rapidly to nutrient additions, decomposition may respond much more slowly to added nutrients.

Modelling effects of litter quality and environment on peat accumulation over different time‐scales

1 A model was developed that simulates the production and decay of annual peat cohorts over time-scales from years to millennia. The model was used to investigate potential effects of environment and litter-quality related parameters on peat accumulation, and to examine how well past changes in net accumulation can be reconstructed from the peat core record. 2 Sensitivity analysis of the model indicates that the relative ability of different input parameters to increase peat accumulation changed over time. Short-term results, e.g. from litter decomposition studies, therefore cannot be extrapolated to predict peat accumulation over longer time-scales. 3 In simulations that examined the long-term development of static community types, peat accumulation responded more strongly to water table position in bogs than in fens. In several cases, the relative peat accumulation potential of different community types changed over time. 4 Successional change (fen to bog) increased or decreased net peat accumulation, depending on the water table of the simulated bog. If succession was accompanied by lowered water tables, modelled peatlands showed a net loss of organic matter over extended periods of time. Effects of decreased litter quality in drier communities were outweighed by decreased productivity and greater decomposition in the thicker acrotelm. 5 Plots of cumulative organic matter mass vs. age for simulated profiles were often ‘concave’, as predicted by models that assume continued decomposition of deep peat. However, simulations that involved community change violated the assumptions of such models, and reconstructed actual (net) rates of organic matter accumulation were unreliable in spite of excellent model fits. 6 Current peat accumulation models often assume that environmental change will affect productivity, but not the botanical composition of peatland communities. Over decadal and centennial time-scales, however, community change will probably play a key role in determining peatland responses to climate change. Results obtained here suggest that interactions between environmental and community-based controls are complex, and their net effect may not be predictable from current data. In order to develop predictive models that work over these time-scales, we need a better understanding of feedback mechanisms between hydrology, community composition, and organic matter accumulation in peatlands.

Decomposition of litter in a dry sclerophyll eucalypt forest and a Pinus radiata plantation in southeastern Australia

AbstractThis study of litter decomposition was part of an extensive project examining the partitioning of rainfall, the associated chemistry, and litterfall in a dry sclerophyll eucalypt forest and a Pinus radiata plantation in southeastern Australia. The eucalypt species studied were Eucalyptus rossii, E. mannifera and E. dives. The components tested were Pinus radiata needles, leaves of the three eucalypt species, and the bark of E. rossii and E. mannifera.During the first 16 weeks of the decomposition experiment there was a rapid decrease in the concentrations of potassium, magnesium, sodium and phosphorus; this was attributed to leaching. During this period, concentrations of nitrogen and calcium increased for most components. After this period, decomposition became the dominant process, during which the concentrations of most elements increased. By the end of the experiment there was, compared with the initial values, a marked reduction in concentrations of sodium, magnesium and potassium for all eucalypt and pine litter. Calcium concentrations increased through time, with eucalypt bark showing a mid‐period decline. Phosphorus concentrations decreased for the eucalypt leaves but increased substantially for the pine needles and the eucalypt bark. For all components of both the eucalypts and pines, total nitrogen concentrations rose consistently throughout the decomposition period. This was attributed to the formation of nitrogen‐substituted lignin, which was more resistant to decomposition than the other nitrogen‐containing compounds, as well as some nitrogen being stored in the micro‐organisms responsible for decomposition. Because of loss of fragmented litter from the litter bags after 16 weeks, the weight changes could not be confidently measured after this period. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Variability in litter quality and its relationship to litter decay in Canadian forests

Predicting the effects of climate change on litter decomposition requires an improved understanding of the link between organic composition and the parameters used to define litter quality. Carbon-13 nuclear magnetic resonance spectroscopy with cross-polarization and magic-angle spinning (CPMAS NMR) was used to characterize 36 foliar litters, including the species used in the Canadian Intersite Decomposition Experiment (CIDET), a Canada-wide long-term litter decomposition study. The litters showed a wide range of organic composition, qualitatively interpreted as the sum of component biopolymers (mainly carbohydrates, cutin, tannins, and lignin). Only weak correlations were found between NMR parameters and Klason lignin (KLIG); however, cluster analysis based on elemental, NMR, and proximate analysis gave good separation of botanical classes. NMR also had little predictive value for 3-year CIDET mass losses, which were negatively correlated with both KLIG and KLIG/N. Mass loss generally decreased in the following order: grass &gt; pioneer broad-leafed deciduous &gt; conifer (deciduous and evergreen) &gt; American beech (a fagaceae) &gt; wood. Predictive models for 3-year CIDET mass loss derived from linear regression with elemental, proximate, and NMR analyses were superior to those using only NMR parameters, with the best model based on KLIG, N, and Ca. Although providing no molecular-level understanding, KLIG integrates the most insoluble lignin, cutin, and tannin components. Limitations and possible improvements for NMR evaluation of litter quality are discussed.Key words: Klason lignin, 13C CPMAS NMR, proximate analysis, litter decomposition, tannin, cutin, CIDET.

Variability in litter quality and its relationship to litter decay in Canadian forests

Predicting the effects of climate change on litter decomposition requires an improved understanding of the link between organic composition and the parameters used to define litter quality. Carbon-13 nuclear magnetic resonance spectroscopy with cross-polarization and magic-angle spinning (CPMAS NMR) was used to characterize 36 foliar litters, including the species used in the Canadian Intersite Decomposition Experiment (CIDET), a Canada-wide long-term litter decomposition study. The litters showed a wide range of organic composition, qualitatively interpreted as the sum of component biopolymers (mainly carbohydrates, cutin, tannins, and lignin). Only weak correlations were found between NMR parameters and Klason lignin (KLIG); however, cluster analysis based on elemental, NMR, and proximate analysis gave good separation of botanical classes. NMR also had little predictive value for 3-year CIDET mass losses, which were negatively correlated with both KLIG and KLIG/N. Mass loss generally decreased in the fo...

Monopolization of litter processing by a dominant land crab on a tropical oceanic island.

Litter processing by macroinvertebrates typically involves suites of species that act together to determine rates of breakdown and decomposition. However, tropical oceanic islands and coastal fringes on continents are often dominated by one or a few species of omnivorous land crabs that consume leaf litter. We used an exclusion experiment, together with other leaf removal and litter decomposition studies, to assess the role of a single dominant species, the red crab (Gecarcoidea natalis), in litter dynamics in rain forest on Christmas Island, Indian Ocean. In the presence of red crabs, litter cover and biomass varied seasonally, from almost complete cover and high biomass at the end of the dry season to almost total absence of litter at the end of each wet season. When crabs were excluded from both the shaded understory and light gaps in rain forest, litter increased rapidly to almost complete cover, which was then maintained year round. Leaf tether experiments, and measures of litter input and standing crops, indicated that red crabs monopolize litter processing, removing between 39 and 87% of the annual leaf fall from the forest floor. Rates of litter turnover were over twice as high in the presence of land crabs: the decomposition constant, k, was 2.6 in the understory exclusion plots, but rose to 6.0 in the presence of crabs. Red crabs occur at biomass densities (114 g m-2) far greater than those reported elsewhere for entire litter faunas. They significantly reduced the abundance of other litter invertebrates, but we did not detect any change in the relative frequencies of the major invertebrate groups (mites, collembolans, pulmonate snails, ants, psocopterans, and spiders). Wherever omnivorous land crabs are abundant, their activities may be paramount in litter decomposition and in regulating the rate of nutrient cycling. In monopolizing litter processing, they may also be important physical "ecosystem engineers", translocating organic matter and nutrients into the soil and reducing available habitat for other animals.

Influence of modern soil restoration techniques on litter decomposition in forest soils

The study assesses the influence of various soil preparation techniques for afforestation on litter decomposition in replanted forest soils. Techniques were compared in three different study areas in the western part of Germany on gleyic, dystric cambisol and gleyic luvisol soil types. The mechanical soil preparation techniques compared was part of a comprehensive restoration of acidic and partially compacted forest soils on previously wind-blown sites which includes soil loosening, mixing and liming of the top horizons up to a depth of 40 to 50 cm. Litter decomposition studies were done using the minicontainer method of Eisenbeis (1993, 1994)and Eisenbeis et al. (1995). Minicontainers with mesh sizes of 25, 250 and 2500 μm were implanted vertically into the soil up to a depth of 25 cm and were collected after 2, 6, 12, 24 and 48 weeks. Mesh sizes were so chosen to selectively include the litter decomposition activity of the microflora and the meso- and macrofauna, respectively over time and at different soil depths. Distinct differences in litter decomposition rates were found between study areas, soil preparation techniques, soil depth and mesh sizes. The decomposition rate increased in the order gleyic luvisol, dystric cambisol and gleyic cambisol. Litter decomposition was greater as a result of mechanical soil preparation and liming. In mechanically prepared soils, the extent of litter decomposition was less in the top horizon (0–6 cm) than in unprepared soil and greater at 6–24 cm soil depth. The greatest rates of litter decomposition occured when the total ground area was mechanically mixed compared with soil preparations restricted to loosened strips. After soil milling, soil properties as well as litter decomposition were more homogeneous as compared with soil loosening treatments. We conclude that, nearly two years after the total soil restoration process, all functional groups of soil organisms have been re-established. The minicontainer-test proved to be a valuable tool in studying litter mass loss in the soil profile.

Nitrogen and Carbon Soil Dynamics in Response to Climate Change in a High-elevation Ecosystem in the Rocky Mountains, U.S.A.

We have implemented a long-term snow-fence experiment at the Niwot Ridge Long-Term Ecological Research (NWT) site in the Colorado Front Range of the Rocky Mountains, U.S.A., to assess the effects of climate change on alpine ecology and biogeochemical cycles. The responses of carbon (C) and nitrogen (N) dynamics in high-elevation mountains to changes in climate are investigated by manipulating the length and duration of snow cover with the 2.6 × 60 m snow fence, providing a proxy for climate change. Results from the first year of operation in 1994 showed that the period of continuous snow cover was increased by 90 d. The deeper and earlier snowpack behind the fence insulated soils from winter air temperatures, resulting in a 9°C increase in annual minimum temperature at the soil surface. The extended period of snow cover resulted in subnivial microbial activity playing a major role in annual C and N cycling. The amount of C mineralized under the snow as measured by CO2 production was 22 g m−2 in 1993 and 35 g m−2 in 1994, accounting for 20% of annual net primary above-ground production before construction of the snow fence in 1993 and 31% after the snow fence was constructed in 1994. In a similar fashion, maximum subnivial N2O flux increased 3-fold behind the snow fence, from 75 μg N m−2 d−1 in 1993 to 250 μg N m−2 d−1 in 1994. The amount of N lost from denitrification was greater than the annual atmospheric input of N in snowfall. Surface litter decomposition studies show that there was a significant increase in the litter mass loss under deep and early snow, with no significant change under medium and little snow conditions. Changes in climate that result in differences in snow duration, depth, and extent may therefore produce large changes in the C and N soil dynamics of alpine ecosystems.

Effects of leaf litter mixtures on the decomposition of Quercus serrata and Pinus densiflora using field and laboratory microcosm methods

The decay rate, respiration rate and nitrogen dynamics of mixed Quercus serrata Murray and Pinus densiflora Sieb et. Zucc. leaf litter were studied for 1 year using field and greenhouse microcosms (GM) and litterbag (LB) methods. The study aimed to determine the effect of mixing two types of litter with contrasting physical and chemical properties. It also evaluated the suitability of using laboratory microcosms in decomposition studies using mixed litter. Results indicate that combined weight losses were affected by both litter mixtures and incubation chambers. Decay rate of Quercus was enhanced in field microcosms (FM) compared to LBs while that of Pinus was not. The decay rates of both litter types were significantly suppressed in GM as compared to field set up (FM and LB) which were comparable. Observed combined weight losses of mixed litter were higher than predicted based on single litter decomposition assays, suggesting a positive enhancement effect. Mixed litter had higher biological activities, indicated by litter respiration rates and mediated the decay process. Observed N contents of Pinus litter were higher than predicted, while the observed values of Quercus were lower than predicted based on data from pure litter, due to interactive effect of mixed litter. Nutrient translocation from nutrient-rich litter ( Quercus) to nutrient-poor ( Pinus) litter had occurred. It is then inappropriate to use data derived from pure litter decomposition studies to estimate the nutrient dynamics of mixed forest stands because it may be either under- or over-estimated, depending on the type of litter and the rate of mixture.

Nitrogen and Carbon Soil Dynamics in Response to Climate Change in a High-Elevation Ecosystem in the Rocky Mountains, U.S.A.

We have implemented a long-term snow-fence experiment at the Niwot Ridge Long-Term Ecological Research (NWT) site in the Colorado Front Range of the Rocky Mountains, U.S.A., to assess the effects of climate change on alpine ecology and biogeochemical cycles. The responses of carbon (C) and nitrogen (N) dynamics in high-elevation mountains to changes in climate are investigated by manipulating the length and duration of snow cover with the 2.6 x 60 m snow fence, providing a proxy for climate change. Results from the first year of operation in 1994 showed that the period of continuous snow cover was increased by 90 d. The deeper and earlier snowpack behind the fence insulated soils from winter air temperatures, resulting in a 90C increase in annual minimum temperature at the soil surface. The extended period of snow cover resulted in subnivial microbial activity playing a major role in annual C and N cycling. The amount of C mineralized under the snow as measured by CO2 production was 22 g m-2 in 1993 and 35 g m-2 in 1994, accounting for 20% of annual net primary aboveground production before construction of the snow fence in 1993 and 31% after the snow fence was constructed in 1994. In a similar fashion, maximum subnivial N20 flux increased 3-fold behind the snow fence, from 75 ?xg N m-2 d-' in 1993 to 250 ?xg N m-2 d-' in 1994. The amount of N lost from denitrification was greater than the annual atmospheric input of N in snowfall. Surface litter decomposition studies show that there was a significant increase in the litter mass loss under deep and early snow, with no significant change under medium and little snow conditions. Changes in climate that result in differences in snow duration, depth, and extent may therefore produce large changes in the C and N soil dynamics of alpine ecosystems.

Long-term study of litter decomposition on a Pennine peat bog: which regression?

It is estimated that in the northern hemisphere one-third of the world pool of soil carbon is contained in peat resulting from an incomplete decomposition of plant remains. The time course for the decomposition of the predominant plant litters on a Pennine moorland in northern England is reported for a study extending over 23 years. Spatial variation of the weight remaining of decomposing litters increased with time. This experimental study gave an age for the upper layers of the bog and a curve for long-term decay based on direct observation rather than inferred from profile samples or from short-term observations. It showed that short-term observations can give misleading results in the long term, with a variety of litters with differing early decay rates ultimately making a similar contribution to accumulation. Spatial variation of the weight remaining of the decomposing litters increased with time, so that variation within micro-environments, or within apparantly uniform substrates, may contribute significantly to organic matter accumulation. An asymptotic curve best described the long-term course of decomposition leading to the accumulation of peat. The use of the model for the three litter types, Calluna vulgaris, Eriophorum vaginatum and Rubus chamaemorus, is described and the implication of the results for modelling of organic matter accumulation are then discussed.

Comparative study of litter decomposition and mineral element release in two amazonian forest ecosystems: litter bag experiments

Comparative study of litter decomposition and mineral element release in two amazonian forest ecosystems: litter bag experiments