Leaf Litter Decay Research Articles

Do Melaleuca ericifolia SM. leaves suppress organic matter decay in freshwater wetlands?

Essential oils of paperbarks, Melaleuca spp., have been shown in laboratory studies to inhibit bacterial activity and slow the rate of cellulose decay. Field (Gippsland Lakes, south-eastern Victoria, Australia) and glasshouse experiments were conducted to test the hypothesis that leaves of Melaleuca ericifolia SM. (the swamp paperbark) suppressed the decay of leaf litter under conditions existing or mimicking those in natural wetlands. Under field conditions, neither brown nor green M. ericifolia leaves, at loadings that would normally occur in a typical paperbark wetland and over a range of leaf-mass ratios, significantly affected the decay rate of two common freshwater macrophytes, Triglochin procerum (water ribbon) and Phragmites australis (common reed). In contrast, glasshouse experiments showed that Melaleuca ericifolia leaves (both intact and ground, and both brown and green) suppressed decay of T. procerum when placed in moist conditions on the sediment surface. However, no inhibitory effect was observed when leaves were flooded. Purified, commercially available Melaleuca essential oil (extracted from Melaleuca alternifolia leaves) decreased the rate at which T. procerum leaves decayed under glasshouse conditions by as much as 43 %. As with entire leaves, the inhibitory effect of purified Melaleuca essential oil was greatest when the leaves were placed in moist, but not submerged, conditions. Experiments designed to test the possibility that the inhibition was due to a simple, physical (coating) effect rather than metabolic inhibition of microbes showed clearly that the effect was not due simply to the hydrophobic nature of essential oils. This study indicates that M. ericifolia leaf litter in freshwater wetlands probably exerts only a small effect on the rate at which leaves from other wetland plant species decay. Any inhibitory effect is likely to be greater after water levels drop (e.g., seasonally in a Mediterranean climate) and remaining leaf material is left moist on the surface of water logged sediments than when material is totally submerged, as during the wetland's high water phase.

Decomposition of leaf and root litter of Chihuahuan desert shrubs: effects of three years of summer drought

One of the more uncertain aspects of nutrient cycling in desert ecosystems is the extent to which decomposition is controlled by water availability. Some of this uncertainty may be partly related to the duration of the studies and/or differences in the chemical composition of the decaying litter. We conducted a 3-year field study of rainfall to determine the impact of summer (June – September) drought on decomposition of leaf and root litter of two shrub species ( Larrea tridentata and Prosopis glandulosa) in the northern Chihuahuan Desert (New Mexico, U.S.A.). In both species, leaf litter decayed at a faster rate and was less effected by drought than root litter. Drought had no influence on the rates of decomposition of leaves of either species during the first 18 months, but caused decay rates to decline by about 25% during the latter half of the study. Drought decreased decay of root litter in both species by about 25% throughout the 3 years. There was a general increase in percent nitrogen (%N) of decomposing leaf litter in both species. Root litter %N declined slightly in Larrea but remained relatively constant in Prosopis. Using a modified version of the CENTURY model, we were able to predict most aspects of observed leaf and root litter mass loss and nitrogen dynamics. Overall, the results of this study suggest that relatively large changes in precipitation produce comparatively small changes in rates of decay of both leaf and root litter.

Effect of inorganic nutrients on relative contributions of fungi and bacteria to carbon flow from submerged decomposing leaf litter.

The relative contributions of fungi and bacteria to carbon flow from submerged decaying plant litter at different levels of inorganic nutrients (N and P) were studied. We estimated leaf mass loss, fungal and bacterial biomass and production, and microbial respiration and constructed partial carbon budgets for red maple leaf disks precolonized in a stream and then incubated in laboratory microcosms at two levels of nutrients. Patterns of carbon flow for leaf disks colonized with the full microbial assemblage were compared with those colonized by bacteria but in which fungi were greatly reduced by placing leaf disks in colonization chambers sealed with membrane filters to exclude aquatic hyphomycete conidia but not bacterial cells. On leaves colonized by the full microbial assemblage, elevated nutrient concentrations stimulated fungi and bacteria to a similar degree. Peak fungal and bacterial biomass increased by factors of 3.9 and 4.0; cumulative production was 3.9 and 5.1 times higher in the high nutrient in comparison with the low nutrient treatment, respectively. Fungi dominated the total microbial biomass (98.4 to 99.8%) and cumulative production (97.3 and 96.5%), and the fungal yield coefficient exceeded that of bacteria by a factor of 36 and 27 in low- and high-nutrient treatments, respectively. Consequently, the dominant role of fungi in leaf decomposition did not change as a result of nutrient manipulation. Carbon budgets indicated that 8% of leaf carbon loss in the low-nutrient treatment and 17% in the high-nutrient treatment were channeled to microbial (essentially fungal) production. Nutrient enrichment had a positive effect on rate of leaf decomposition only in microcosms with full microbial assemblages. In treatments where fungal colonization was reduced, cumulative bacterial production did not change significantly at either nutrient level and leaf decomposition rate was negatively affected (high nutrients), suggesting that bacterial participation in carbon flow from decaying leaf litter is low regardless of the presence of fungi and nutrient availability. Moreover, 1.5 and 2.3 times higher yield coefficients of bacteria in the reduced fungal treatments at low and high nutrients, respectively (percentage of leaf carbon loss channeled to bacterial production), suggest that bacteria are subjected to strong competition with fungi for resources available in leaf litter.

Hyphomycetes from Nigerian rain forests

Phaeobotrys gen. nov., based on Phaeodactylium acutisporum, characterized by branched and pigmented conidiophores, and the production of hyaline, appendiculate conidia from denticles on polyblastic conidiogenous cells which usually extend sympodially to form more conidiogenous loci, and Zanclospora stellata sp. nov., recognized by its stellate sterile branches in the distal part of the conidiophore and bacilliform conidia, are described and illustrated from decaying leaf litter from Nigeria. Keys to Phaeobotrys and related genera, and to species of Zanclospora are proposed. Furthermore, a list of hyphomycetes newly reported for Nigeria is provided.

Processing of leaf litter in acid waters of the post-mining landscape in Lusatia, Germany

Most surface waters of the post-mining landscape in Lusatia, Germany, are characterised by severe acidity (pH<3.0). To check leaf litter decay in this environment, the first stages of leaf processing were studied under laboratory conditions and leaf breakdown rates were determined in long-term experiments in situ. The laboratory experiments exhibited leaching of soluble compounds identical to leaching in neutral water. Microbial conditioning differed strongly in acidic waters from the neutral control. In the acidic water intensive colonisation of leaves by fungi compensated for mass loss due to leaching. Phenols, known to inhibit fungal growth, could not be found in the acidic water. The long-term litter bag experiments showed very low breakdown rates (− k=0.0014–0.0037 d −1). Absence of shredders and moderate flow regime prevented fragmentation of leaves. Precipitation of ochre seemed to inhibit colonisation by microbial decomposers and slow down leaf decay. The incomplete leaf breakdown will lead to a specific hyporheic environment with large interstices and rapid growing sediments. This has to be considered in restoration and management of streams of the post-mining landscape.

Author Index of Volume 257

The responses of major meiofaunal taxa and nematode species assemblage to the decaying leaf litter of the mangrove Kandelia candel were investigated through a field colonization experiment in subtropical Hong Kong. Sixty-four replicate azoic and organic-free sediment cores were treated with leaf litter additions of 0×, 0.5×, 1× and 2× natural sediment organic concentration, respectively, and retrieved 1, 10, 30 and 60 days post-placement. Replicate cores of ambient sediment were also taken at each sampling date to provide baseline information. Results of ANOVAs suggested that either different meiofaunal taxa responded to the leaf litter in different ways or the response of the same taxon changed over decomposition time. Multivariate ordination performed on nematodes revealed an alteration in community structure after 10, 30 and 60 days between controls and treatments. This alteration was attributed to some deposit feeding nematodes, particularly a bacterivorous species, Diplolaimella sp., which bloomed in all the cores treated with leaf litter, testifying to the important role such meiofauna plays in the process of detritus decomposition.

10 The importance of leaf litter decay processes to container-breeding mosquito' performance

10 The importance of leaf litter decay processes to container-breeding mosquito' performance

Effects of leaf litter addition on meiofaunal colonization of azoic sediments in a subtropical mangrove in Hong Kong.

The responses of major meiofaunal taxa and nematode species assemblage to the decaying leaf litter of the mangrove Kandelia candel were investigated through a field colonization experiment in subtropical Hong Kong. Sixty-four replicate azoic and organic-free sediment cores were treated with leaf litter additions of 0x, 0.5x, 1x and 2x natural sediment organic concentration, respectively, and retrieved 1, 10, 30 and 60 days post-placement. Replicate cores of ambient sediment were also taken at each sampling date to provide baseline information. Results of ANOVAs suggested that either different meiofaunal taxa responded to the leaf litter in different ways or the response of the same taxon changed over decomposition time. Multivariate ordination performed on nematodes revealed an alteration in community structure after 10, 30 and 60 days between controls and treatments. This alteration was attributed to some deposit feeding nematodes, particularly a bacterivorous species, Diplolaimella sp., which bloomed in all the cores treated with leaf litter, testifying to the important role such meiofauna plays in the process of detritus decomposition.

MICROBIAL ENZYME SHIFTS EXPLAIN LITTER DECAY RESPONSES TO SIMULATED NITROGEN DEPOSITION

Some natural ecosystems near industrialized and agricultural areas receive atmospheric nitrogen inputs that are an order of magnitude greater than those presumed for preindustrial times. Because nitrogen (N) often limits microbial growth on dead vegetation, increased N input can be expected to affect the ecosystem process of decomposition. We found that extracellular enzyme responses of a forest-floor microbial community to chronically applied aqueous NH4NO3 can explain both increased and decreased litter decomposition rates caused by added N. Microbes responded to N by increasing cellulase activity in decaying leaf litter of flowering dogwood, red maple, and red oak, but in high-lignin oak litter, the activity of lignin-degrading phenol oxidase declined substantially. We believe this is the first report of reduced ligninolytic enzyme activity caused by chronic N addition in an ecosystem. This result provides evidence that ligninolytic enzyme suppression can be an important mechanism explaining decreased ...

Evaluation of Bacterial Recovery Efficiency and Counting Precision from Decaying Leaf Litter in Little Rock Lake, Wisconsin, USA

We studied the effectiveness of sonication and filter-size-fractionation to efficiently remove and separate bacterial leaf-surface colonizers from other members of the microbial community. Leaf discs from red oak and paper birch leaves were colonized in situ for 8 and 22 days in Little Rock Lake, WI, and sonicated at 90 W power output for 60 seconds, followed by filter-fractionation (3.0 μm) to remove and isolate bacteria. This technique consistently yielded the highest bacterial activity (relative Electron Transport System activity) and resulted in bacterial recovery efficiencies from leaf surfaces ranging from 96.5% to 98.8%. In addition, comparisons among various methods currently used to estimate bacterial densities (e.g., malachite green-INT, acridine orange direct counts, scanning electron microscopy approaches) were completed to assess the utility of the MINT method for counting bacteria removed by sonication. Bacterial counts derived from MINT and AODC methods were never significantly different, but always were significantly higher and less variable than counts from SEM. Finally, an attempt was made to address sources of variability in counting precision using the MINT method for bacteria removed from leaf surfaces. For two leaf species, on two sampling dates, most of the variability in MINT cell counts was due to variability among microscopic fields counted, while little was due to either subsample or filter used in cell counts. Thus, the combination of sonication and filter-size-fractionation to remove bacterial leaf surface colonizers appears to be an effective approach, allowing reproducible and precise measurements of bacterial densities and activities.

Microbial biomass and production associated with decaying leaf litter of the emergent macrophyte Juncus effusus

Emergent macrophytes are a major source of organic matter production in freshwater wetlands, and often represent the bulk of the plant material entering the detrital pool. We examined the decomposition and microbial dynamics associated with litter of the emergent macrophyte, Juncus effusus (soft rush), during its movement from an aerial standing dead to a submerged decay environment. Standing dead leaves of J. effusus were collected after an initial period of standing litter microbial decay, placed in 1‐mm mesh litter bags, and submerged in a wetland. Litter bags were retrieved periodically over 268 d and analyzed for microbial (fungal and bacterial) biomass and production, ATP concentrations, litter mass loss, and quality (C:N:P and plant fiber). Submerged litter decay of J. effusus was slow (k = 0.0010 d−1), with only 23% weight loss after 268 d. Both fungal and bacterial biomass and production decreased significantly soon after standing plant litter was submerged in the wetland surface waters. Despite decreases in microbial biomass and production, fungal decomposers remained the dominant microbial assemblage associated with decaying plant litter, accounting for 99% and 91% of the total microbial biomass and production, respectively. Mean fungal production ranged from 73–2,836 mg C g−1 AFDM d−1 (AFDM: ash‐free dry mass remaining) during the study period, whereas attached bacterial production ranged from 4–32 mg C g−1 AFDM d−1. Patterns of litter ATP and nutrient concentrations (N and P) were similar to those observed for fungal and bacterial biomass, suggesting that at least a portion of the detrital N and P may have been incorporated into microbial biomass. Significant changes in microbial colonization and activity associated with emergent macrophyte litter can occur following the collapse of standing dead plant matter to the water or surface sediments. Furthermore, our findings suggest that fungi are significant contributors to the decay of coarse particulate plant matter in wetland ecosystems.

Fine litter chemistry, early-stage decay, and nitrogen dynamics under plantations and primary forest in Lowland Amazonia

One year field exposures of leaf litter from replicated plots of Pinus caribaea var. hondurensis Barrett and Golfari, Carapa guianensis Aubl., Euxylophora paraensis Hub., a Leguminosae combination ( Dalbergia nigra Fr. All., Dinizia excelsa Ducke, Parkia multijuga Benth.), and adjacent upland ( terra firme) forest at the Curuá-Una Forest Reserve, Pará, Brazil were used to examine the factors controlling leaf litter decay and N dynamics in a lowland tropical environment. Initial leaf litter N concentrations ranged from 4.4 ( P. caribaea) to 16.3 mg g −1 dry matter (Leguminosae), and initial lignin concentrations from 190.8 (Leguminosae) to 459.3 mg g −1 dry matter (forest). Pinus caribaea leaf litter lost the least mass (28%), and the Leguminosae leaf litter the most (61%), during the year long incubations. Initial and 1-y proximate C fractions, N concentrations and polyphenol concentrations were not related to mass loss. Annual N accumulation or depletion from leaf litter under the plantations and forest was related to C loss ( R 2=0.93, P=0.007) and holocellulose loss ( R 2=0.84, P=0.02). When leaf litter was placed outside its stand of origin, there was a significant location effect on decay rates, indicating that differences in the physical and biological microenvironments under the monospecific plots affected litter decomposition.

Freshwater Sponge Gemmules Survive Months of Anoxia

Gemmules of Ephydatia muelleri, exposed to anoxic conditions (nitrogen) in sealed glass ampules, generally showed no differences from oxic controls in hatchability or hatching rate over exposure periods of 1 to 112 days. Unlike controls, hatching was totally inhibited under anoxia at +20?C. Our results directly demonstrate that this species, and probably many freshwater sponges, can survive seasonal anoxia in the gemmule stage. High gemmule survival under nitrogen also permits them to be stored and transported without regard for external temperature. These results are consistent with existence of an ametabolic state under anoxia, but much more detailed work is needed to prove this conjecture. Additional key words: Spongillidae, respiration, cold-tolerance, dormancy, hatching Many aquatic invertebrates survive seasonally unfavorable environmental conditions by production of specialized dormant stages, usually encapsulated eggs or embryos (Hochachka & Guppy 1987). In the case of planktonic forms, these stages are usually negatively buoyant, accumulate on and in sediments, and thus form an egg or seed bank with potential long-term viability (Marcus et al. 1994). Immotile benthic invertebrates, such as sponges and bryozoans, typically use non-embryonic stages in a similar survival strategy. Here undifferentiated parental cells, rich in nutrient reserves, aggregate and are encapsulated in a continuous collagen capsule of varying complexity, constituting the gemmules of sponges and statoblasts of bryozoans. In the case of freshwater sponges, a major portion of parental biomass is thereby packaged in myriad, small, resistant gemmules attached more-or-less tightly to either the substratum, the parental skeleton, or both (Simpson & Fell 1974). Recent work on gemmule physiology has dealt with desiccation resistance (Fell 1987; Fell & Bazer 1990), cold hardiness (Fell & Fell 1987; Barbeau et al. 1989; Fell & Levasseur 1991; Ungemach et al. 1997), the characteristics of true diapause (Fell 1990, 1995), and the detailed energetics of the hatching process (Loomis et al. 1996). One component of gemmule survival frequently suggested, but not previously investigated, is an ability to withstand seasonal anoxia. Gemmules attached to exposed rock surfaces in ponds or pools of a Author for correspondence. E-mail: inhr@musicb.mcgill.ca b Present address: Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, P.E.I., C1A 4P3, Canada slow streams are often covered in layers of decaying leaf litter for most of winter. Under such circumstances they would likely be exposed to hypoxic and anoxic conditions for periods of weeks or months before spring flush-out. Gemmules of sponges that grow on macrophytes fall to the lake or pond floor during late fall die-back of their substrate and are thus exposed to the organic-rich, anoxic sediment surface for months (Frost et al. 1982; Frost 1991). In both cases, new sponges arise at the onset of spring mixing and reoxygenation of the microhabitat, and it seems likely that this repopulation is due to hatching of gemmules that have survived months of reduced oxygen availability. Repeated observations that gemmules collected for laboratory study survive for weeks or months in closed jars or vials with decaying parental tissues or in high densities in small amounts of water, which are almost certainly anoxic, under refrigeration at 0-4?C also suggest an ability to survive without oxygen (Fell 1993, 1994). Because over-winter survival under anoxia would appear to be of such importance to many sponge populations in nature, and because this phenomenon may provide important clues to the physiological processes controlling dormancy in this group, we decided to examine gemmule survival experimentally. We tested the gemmulehatching success of a locally abundant freshwater sponge in the absence of oxygen over an ecologically significant time scale.

Do mangrove diversity and leaf litter decay promote meiofaunal diversity?

The effects of mangrove diversity and the process of leaf litter decay on the diversity and community structure of meiofauna inhabiting leaf litter were investigated in a simple field experiment in a wet, tropical, soft sediment, mangrove forest in north-eastern Malaysia. Strings of freshly fallen leaves of Rhizophora apiculata and Bruguiera parviflora were placed on the mud surface in two adjacent subplots, each dominated by one of these tree species. The leaf strings were sampled weekly over five weeks and the nematodes and copepods found on the leaves were identified to species and enumerated. It is shown that, under similar conditions of sediment composition, salinity and tidal inundation, the species of mangrove tree or their leaves have little influence on leaf litter meiofaunal climax communities. Such differences as are apparent in the early part of the experiment are probably the result of differences in tree root structure, associated macrofauna and the initial chemical composition of the leaves. It is also shown that there are significant differences in the litter meiofaunal communities during the process of leaf litter decay. For the copepods, a distinct leaf litter community is characterized by the presence of members of the family Darcythompsoniidae and it is the completion of their lifecycle which is the principal feature of the community changes. Development of the nematode community is characterized by subtle shifts in the composition of species inhabiting the leaf litter. It is suggested that changes in the meiofauna community may be more intimately linked to successional changes in the chemistry and/or microflora of the leaf litter than to the physical breakdown of the substratum.

A Tailed Frog (Ascaphus truei) Nest Site in Northwestern California

The tailed frog (Ascaphus truei) inhabits streams in the Pacific Northwest, Idaho, and Montana (Nussbaum and others 1983). Few nests of A. truei have been reported and nest sites and time of oviposition are not well known. Daugherty and Sheldon (1982) determined oviposition occurred in June in Montana populations. Brown (1989) collected females with mature eggs in early July in NW Washington. Adams (1993) discovered a nest with 27 eggs in the Oregon Coast Range in August 1991 that may have consisted of 3 different clutches, based on varying developmental stages. Nest sites of A. truei have not been documented previously in California. On 16 August 1994, we discovered an A. truei nest site approximately 15 km N of Trinidad, Humboldt County, California in the McDonald Creek drainage. Twenty-eight eggs were attached to the underside of a boulder (44x28 cm) in a pool of a 2nd-order stream (4.3-m wide), 8 km inland from the Pacific Ocean. The pool (40x20x10 cm) received continuous water flow. The nest site occurred on private forest land in a SW-facing stream with 18% gradient. Water temperature was 15.9°C at 1700 hr. Overstory vegetation was primarily 45 yr-old coast redwood (Sequoia sempervirens) and red alder (Alnus rubra), with 90% canopy closure (measured with a densiometer). The nest site was 23.5 m below a road culvert and 0.7 m above the stream's confluence with a 3rd-order fishbearing stream. We observed the nest from 16 August through 20 September 1994. Three eggs were destroyed when the boulder was turned over, but 25 eggs remained intact in a loose string beneath the boulder. The eggs were cream-colored, each approximately 5 mm in diameter. No potential predators were seen in the pool during the observation period, but 5 larval Pacific giant salamanders (Dicamptodon tenebrosus) and 1 adult A. truei were found within the 24.2 m stream reach surveyed on 16 August 1994. The tailed frog nest site was located 0.7 m above the downstream end of the surveyed reach. On 26 August, 8 tadpoles were observed in the pool, and 8 eggs remained attached to the boulder. On 2 September, 23 tadpoles were observed in the pool, and no unhatched eggs remained. Tadpoles were easily counted due to the depth of the pool (10 cm), substrate size (sand <2 mm in diameter), and the clarity of the water. During the observation period varying numbers (8 to 23) of tadpoles were observed in the pool, indicating movement of tadpoles between the natal pool and other regions of the stream. No attempts were made to locate tadpoles outside of the pool. On 20 September, 5 tadpoles were measured and averaged 20 mm. The tadpoles were dark gray in color, and each had developed the characteristic white tail spot. Three tadpoles were attached to a boulder, indicating functioning oral discs. We filled a plastic container with decaying leaf litter and gravel, punched numerous holes in all sides, and anchored it in the stream with boulders. Two tadpoles were placed in the container for future measurements. On 20 October, no tadpoles were observed around the nest site. The 2 tadpoles in the plastic container were measured (22 mm and 23 mm, respectively) and released. Oviposition by A. truei apparently occurs between late June and early August (Adams 1983, Daugherty and Sheldon 1982). The clutch found in California probably was deposited in late July and consisted of only 1 clutch because of the uniform developmental stage of the eggs upon discovery, the brief period over which hatching occurred, and their attachment to the boulder in 1 continuous string. Mean clutch sizes reported for inland areas range from 63 eggs in Washington (Brown 1975) to 75 eggs in Montana (Franz 1970). Although we do not know if any predation of eggs occurred before their discovery, the clutch size (N = 28) of the California nest is consistent with others reported for coastal A. truei (Adams 1993, Noble and Putnam 1931). This supports the hypothesis (Adams 1993) that coastal populations may have smaller clutch sizes than inland populations.

Two new species of tardigrades from Short Mountain, Tennessee, U.S.A.

Tardigrades were collected from three seepage spring sites at 549m on Short Mountain, Cannon County, Tennessee. Three terrestrial samples and three aquatic samples were taken monthly from each site. Terrestrial samples included mosses and lichens from rocks and fallen trees; one sample of leaf litter was also collected from two of the sites. Aquatic samples included sediment, decaying leaf litter, and aquatic plants. Specimens of tardigrades were mounted on individual slides in Hoyer's medium. Species were identified and photographed using phase and differential contrast microscopy. Twenty-eight species representing 13 genera were recorded: Pseudechiniscus, Echiniscus, Doryphoribius, Ramazzottius, Hypsibius, Isohypsibius, Diphascon, Platicrista, Itaquascon, Murrayon, Macrobiotus, Minibiotus, and Milnesium. One of the Pseudechmiscus species and an Isohypsibius species were new to science and are described in this paper.

Nitrogen supply effects on productivity and potential leaf litter decay of Carex species from peatlands differing in nutrient limitation.

We investigated the effect of increased N-supply on productivity and potential litter decay rates of Carex species, which are the dominant vascular plant species in peatlands in the Netherlands. We hypothesized that: (1) under conditions of N-limited plant growth, increased N-supply will lead to increased productivity but will not affect C:N ratios of plant litter and potential decay rates of that litter; and (2) under conditions of P-limited plant growth, increased N-supply will not affect productivity but it will lead to lower C:N ratios in plant litter and thereby to a higher potential decay rate of that litter. These hypotheses were tested by fertilization experiments (addition of 10 g N m-2 year-1) in peatlands in which plant growth was N-limited and P-limited, respectively. We investigated the effects of fertilization on net C-fixation by plant biomass, N uptake, leaf litter chemistry and potential leaf litter decay. In a P-limited peatland, dominated by Carex lasiocarpa, there was no significant increase of net C-fixation by plant biomass upon enhanced N-supply, although N-uptake had increased significantly compared with the unfertilized control. Due to the N-fertilization the C:N ratio in the plant biomass decreased significantly. Similarly, the C:N ratio of leaf litter produced at the end of the experiment showed a significant decrease upon enhanced N-supply. The potential decay rate of that litter, measured as CO2-evolution from the litter under aerobic conditions, was significantly increase upon enhanced N-supply. In a N-limited peatland, dominated by C. acutiformis, the net C-fixation by plant biomass increased with increasing N-supply, whereas the increase in N-uptake was not significant. The C:N ratio of both living plant material and of dead leaves did not change in response to N-fertilization. The potential decay rate of the leaf litter was not affected by N-supply. The results agree with our hypotheses. This implies that atmospheric N-deposition may affect the CO2-sink function of peatlands, but the effect is dependent on the nature of nutrient limitation. In peatlands where plant growth is N-limited, increased N-supply leads to an increase in the net accumulation of C. Under conditions of P-limited plant growth, however, the net C-accumulation will decrease, because productivity is not further increased, whereas the amount of C lost through decomposition of dead organic matter is increased. As plant growth in most terrestrial ecosystems is N-limited, increased N-supply will in most peatlands lead to an increase of net C-accumulation.

Lower marine fungi (Labyrinthulomycetes) and the decay of mangrove leaf litter

Lower marine fungi (Labyrinthulomycetes) and the decay of mangrove leaf litter

Lower marine fungi (labyrinthulomycetes) and the decay of mangrove leaf litter

Lower marine fungi (labyrinthulomycetes) and the decay of mangrove leaf litter

Methane Metabolism in a Temperate Swamp

Comparisons between in situ CH(4) concentration and potential factors controlling its net production were made in a temperate swamp. Seasonal measurements of water table level and depth profiles of pH, dissolved CH(4), CO(2), O(2), SO(4), NO(3), formate, acetate, propionate, and butyrate were made at two adjacent sites 1.5 to 2 m apart. Dissolved CH(4) was inversely correlated to O(2) and, in general, to NO(3) and SO(4), potential inhibitors of methanogenesis. At low water table levels (August 1992), maximal CH(4) (2 to 4 muM) occurred below 30 cm, whereas at high water table levels (October 1992) or under flooded conditions (May 1993), CH(4) maxima (4 to 55 muM) occurred in the top 10 to 20 cm. Higher CH(4) concentrations were likely supported by inputs of fresh organic matter from decaying leaf litter, as suggested by high acetate and propionate concentrations (25 to 100 muM) in one of the sites in fall and spring. Measurements of potential CH(4) production (and consumption) showed that the highest rates generally occurred in the top 10 cm of soil. Soil slurry incubations confirmed the importance of organic matter to CH(4) production but also showed that competition for substrates by nonmethanogenic microorganisms could greatly attenuate its effect.