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Notes: Abstract Decomposition of leaves of smooth cordgrass (Spartina alterniflora Loisel.) was monitored for two cohorts of leaves from September 1984 to May 1985 (autumn and winterspring) at Sapelo Island (31°23′ N; 81°17′ W). The leaves were tagged in plance at the ligule, rather than cut and placed in litterbags. Dead leaves were not abscised from shoots. Loss of organic mass from the attached leaves was at least 60 to 68% of the orginal values. Fungal mass, as measured by an enzyme-linked immunosorbent assay, formed 〉 98% of the microbial standing crops in two of three autumn samples, and in all samples for the colder, drier, winterspring cohort. Fungal mass was probably mostly in the form of the mycelium and pseudothecia of an ascomycete, Phaeosphaeria typharum (Desm.) Holm. Fungal dominance of microbial standing crops declined when autumn leaves bent downward and acquired a large sediment content (ash=35% of dry matter); the bacterial crop then rose to 7% of the total microbial crop. Microphotoautotrophic mass was always measurable, but was never more than 2% of the microbial crop. Carbon-dioxide fixation was much lower than carbon-dioxide release, and a substantial portion of the fixation may have been anaplerotic fungal fixation. Threeto 8 wk net fungal productivity (average per day) was much greater (16 to 26 times) than measured instantaneous bacterial productivity (extrapolated to per-day values) early in each decay period. Fungal productivity was negative late in the decay period. Fungal productivity was negative late in the decay period for autumn leaves, and was approximately equal to bacterial productivity late for winter-spring leaves. Net nitrogen immobilization was observed only late in the decay period for autumn leaves, implying that nearly all dead-leaf nitrogen was scavenged into fungal mass after the first sampling interval. Flux estimates for dead-leaf carbon indicated a flow of 11–15% of the original to fungal mass, 2% to bacterial mass, 15–21% to carbon dioxide, 10–12% to dissolved leachage, and 34–36% to small particles; 32–39% remained attached as shreds at the end of the study periods. Salt-marsh periwinkles (Littorina irrorata Say) appeared to be the major shredders of dead leaves and conveyors of leaf-particulate material to the marsh sediment, at least in those parts of the marsh where the snails are densely concentrated (usually areas of short- and intermediateheight cordgrass shoots).

Notes: Abstract The talitrid amphipod Uhlorchestia spartinophila lives in close association with standing-dead leaves of the smooth cordgrass Spartina alterniflora Loisel in salt marshes along the Atlantic coast of North America. This study probed the strength of the trophic link between the amphipod population and the decomposition process in this detrital-based ecosystem. We measured survival, growth and reproductive output in groups of amphipods reared for 6 wk on five diets derived from sheath and blade portions of S. alterniflora leaves just prior to (senescent) and during (dead) decomposition. In unfed treatments, the daily specific mortality rate was 0.391 and starved amphipods survived no longer than 11 d. Among the fed treatments, a diet of senescent sheaths resulted in the lowest survival (20%) and yielded no offspring. Groups fed senescent blades, dead sheaths, dead blades and unwashed dead sheaths had survival rates of 56 to 84% and produced 5.0 to 12.5 offspring replicate−1. Sex ratio usually favored females, but approached unity in treatments with high overall survival, suggesting that quality of available food resources may influence sex ratio in this species. Mean specific growth rates (mm mm−1 d−1) ranged from 0.013 to 0.016, and matched previous estimates of growth from field populations. Overall ecological performance (survival + growth + reproduction) was similar for all food treatments, except senescent sheaths, which yielded a final mean (±SD) dry biomass (0.4 ± 0.42 mg replicate−1) of amphipods significantly lower than that of other diets (1.7 ± 0.81 to 2.6 ± 0.69 mg replicate−1). Natural diets derived from decomposing cordgrass leaves can fulfill the nutritional requirements of U. spartinophila populations, but variation in initial amounts of living fungal biomass among the five experimental diets only partially explained the responses of amphipods in our experiment. Structural characteristics and variation in rates of fungal occupation within different portions of cordgrass leaves may affect the amphipod's ability to access plant production made available by decomposers.

Notes: Abstract Dying leaves ofSpartina alterniflora Loisel (hereafterSpartina) do not undergo abscission and consequently are at least partially degraded while remaining attached to the shoot, i.e., under conditions which may be very different from those occurring in litterbags used to measure decomposition ofSpartina at the sediment surface. Attached living and dead leaves in high-marsh areas are subject to grazing by the abundant gastropodLittorina irrorata Say (hereafterLittorina), a salt marsh periwinkle. In 1986, nitrogen assimilation from living and standing-deadSpartina byLittorina was examined in Sapelo Island (Georgia, USA) salt marshes by labelling plants with the stable nitrogen isotope15N and measuring the transfer into grazing snails in the field. The initial label of ca 8% total plant nitrogen declined to ca 1% over 5 mo, perhaps due to label dilution by less enriched nitrogen taken up and translocated from below- to above-groundSpartina biomass. Snails incorporatedSpartina-derived nitrogen into tissues at rates equal to 10 to 20% of total snail nitrogen 30-d−1 in summer and fall, and 2 to 5% 30-d−1 in winter. In the absence of measurable growth, these high nitrogen incorporation rates may indicate a large reproductive effort, or substantial turnover of somatic tissue nitrogen. The annual total assimilation ofSpartina-derived nitrogen was equal to theLittorina-nitrogen biomass. Assimilation of nitrogen in the presence of livingSpartina material (dead material removed) was reduced substantially below that in the presence of intact plants (living and dead material present).Littorina populations at abundances found in Georgia would assimilate ca 3.4% of above-groundSpartina-nitrogen production annually in high-marsh, short-Spartina areas. Based on preliminary estimates of nitrogen assimilation efficiency, 13.2 to 27.2% of short-Spartina production could be ingested annually by Georgia populations ofLittorina. Most of this ingestion would be concentrated in the summer and early fall, when monthly ingestion could equal 100% of deadSpartina biomass. The impact of grazing byLittorina onSpartina decomposition may be greatest on these early-senescing leaves. Grazing may have little impact on the early stages of decomposition of the bulk of the shoots that senesce later in fall, but may be important in the later stages of decomposition of dead shoots that persist through winter until the following spring and summer.

Notes: Abstract The growth of the salt marsh periwinkleLittoraria irrorata (collected from Sapelo Island, Georgia in 1991, initial shell length 6.2 to 11.5 mm) on various diets was measured. Growth was highest on a diet of standing-dead leaves ofSpartina alterniflora. Periwinkles provided with marsh sediment, yellow-green, sterile, or bacteria-colonized leaves lost organic mass. Fungal-colonized leaves and pure mycelia of fungi common on standing-dead leaves allowed intermediate growth. Growth onS. alterniflora-based diets was negatively correlated with the phenolics content of the food, and positively correlated with its lipid content. No correlation was found between growth and protein content. The digestibility ofS. alterniflora leaves, estimated with the acid-insoluble ash technique, was highest when yellow-green leaves were used. Colonization by fungi or bacteria caused it to decline. ForS. alterniflora-based diets, growth rates were positively correlated with the amount of time spent on the food.

Notes: Abstract  The pathway for the flow of salt-marsh grass production into marsh food-webs is still not well defined. We compared the abilities of three marsh macroinvertebrates [salt marsh periwinkles, Littoraria irrorata (Say) (=Littorina irrorata), salt-marsh coffee-bean snails, Melampus bidentatus (Say); and a talitrid amphipod, Uhlorchestia spartinophila Bounsfield and Heard] to access standing-dead leaves of smooth cordgrass (Spartina alterniflora Loisel). The invertebrates were incubated with naturally-decaying leaves, and the rates of removal of organic matter and living fungal biomass (ergosterol) were measured. The impact of invertebrate activity upon fungal growth rates was measured as rates of fungal-membrane synthesis (incorporation of radioacetate into ergosterol). The removal rates of organic leaf biomass per mg individual biomass were highest for amphipods (700 μg mg−1 d−1) and lowest for periwinkles (90 μg mg−1 d−1), but the relatively large biomass of the snails made their removal rates per individual greater than those of amphipods. Net removal of ergosterol by all three invertebrates was 〉50% for yellow-brown (early-decay) leaf blades. For fully-brown (advanced-decay) blades, 〉50% removal of ergosterol was found only for periwinkles; exposure to coffee-bean snails and amphipods resulted in a net ergosterol reduction of ≤20%. The lower net reduction of living fungal biomass by coffee-bean snails and amphipods may have been due to fungal-growth stimulation (2.3-fold stimulation in coffee-bean snails and 1.5-fold stimulation in amphipods). Grazing by periwinkles did not stimulate fungal growth, possibly because of its high intensity. Grazing by these three salt-marsh shredders may affect marsh-grass shoot-decay in different ways. Periwinkles may abbreviate the period of fungal production, and incorporate the decaying material relatively quickly into snail biomass and fecal-pellet rain to the sediments. Coffee-bean snails and amphipods may enhance and prolong fungal production, along with the formation of fecal-pellet rain. All three invertebrates fed preferentially on leaf blades rather than leaf sheaths, and feeding rates of gastropods were higher during the night than during the day.

Notes: Abstract Phylloplane (leaf surface) algae on leaves from standing dead Spartina alterniflora Loisel in Sapelo Island marshes were enumerated by epifluorescence microscopy. The green alga Pseudendoclonium submarinum Wille dominated algal biovolume on both short-and tall-form plants during summer and winter. Intra-leaf and intra-plant patterns of algal biovolume and diversity indicated that desiccation stress may be an important selective factor. Observed epiphyte densities are 10- to 200-fold lower than values reported for communities on continuously submerged aquatic vegetation. Algal biovolume was less than 10% of that contained in the saprophytic (fungal and bacterial) community.

Notes: 1. We examined standing-senescing, standing-dead and recently fallen leaf blades of Carex walteriana in fens of the Okefenokee Swamp to determine the nature of the microbial decomposers in the early stages of decomposition, measuring both standing crops and productivities ([3H]leucineprotein method for bacteria, [14C]acetateergosterol for fungi).2. Fungal standing crops (ergosterol) became detectable at the mid-senescence stage (leaves about half yellow-brown) and rose to 14–31 mg living-fungal C g−1 organic mass of the decaying system; bacterial standing crops (direct microscopy) were ± 0.2 mgC g−1 until the fallen-leaf stage, when they rose to as high as 0.9 mgC g−1.3. Potential microbial specific growth rates were similar between fungi and bacteria, at about 0.03–0.06 day−1, but potential production of fungal mass was 115–512 μgC g−1 organic mass day−1, compared with 0–22 μgC g−1 day−1 for bacteria. Rates of fungal production were about 6-fold lower on average than previously found for a saltmarsh grass, perhaps because much lower phosphorus concentratiofis in the freshwater fen limit fungal activity.4. There was little change in lignocellulose (LC) percentage of decaying leaves, although net loss of organic mass at the fallen, broken stage was estimated to be 59%, suggesting that LC was lost at rates proportional to those for total organics during decay. Monomers of fungal-wall polymers (glucosamine and mannose) accumulated 2- to 4-fold during leaf decay. This may indicate that an increase found for proximate (acid-detergent) lignin could be at least partially due to accumulation of refractory fungal-wall material, including melanin.5. A common sequence in decaying aquatic grasses is suggested: principally fungal alteration of LC during standing decay, followed by a trend toward bacterial decomposition of the LC after leaves fall and break into particles.

Notes: Summary Dead parts of salt-marsh plants form a considerable fraction of their annual average standing crop. A microbial assemblage living on and in the standing-dead leaves and stems of Spartina alterniflora and Juncus roemerianus responds to saltwater, freshwater or water-vapor wetting by immediately beginning to release CO2. Water-saturated, standing-dead leaves and culms of S. alterniflora release CO2 at steady rates of as much as about 200 and 140 μg CO2−C·g-1 dry·h-1, respectively, at temperatures of 25–30°C, after an initial burst of higher rates. These CO2-release rates are within the range of maximal rates reported for decaying terrestrial litter, and are as high as most rates reported for S. alterniflora decaying under continuously wetted or submerged conditions.

Notes: Abstract The effects of 24 to 72-hr exposure to fenthion (101–103 ppb) were determined for a fungal community, nitrogen-fixing microbes, and representative meiofaunal and zooplankton invertebrates of a mangrove ecosystem. Also tested were the abilities of a benthic diatom and of fungi to grow in the presence of fenthion. Acute lethal, growth-inhibiting, or processdisrupting effects were not detected for exposures to less than 500 ppb fenthion. Results are compared with the findings of several other investigations of the impact of fenthion and other organophosphorus insecticides on non-target organisms.

Notes: Abstract. Ascomycetous fungi are the principal drivers of the decomposition of shoots of smooth cordgrass (Spartina alterniflora). Shoots of smooth cordgrass move into the saltmarsh food web via the decomposition system. Therefore, influences on saltmarsh ascomycetes by pollutants of saltmarshes could have far-reaching impacts. Earlier examination of impacts of severe contamination of a Georgia saltmarsh by mercury and polychlorinated biphenyls (PCBs) revealed little or no influence of the toxicants on living standing crops or sexual productivities of cordgrass ascomycetes. Extension of the examination of saltmarsh-ascomycete response to sites containing other toxic pollutants (the chlorinated organocyclic insecticide toxaphene; chromium, copper, and lead; and polycyclic aromatic hydrocarbons [PAHs]) has shown that none of the additional toxicants engendered saltmarsh-fungal responses in the form of reduced living standing crops or sexual productivities. Thus the ascomycetes of the cordgrass-decay system appear to be as resistant to anthropogenic-pollutant poisoning as smooth cordgrass itself. Unless the fungal and plant resistance mechanisms involve degradation of the toxicants, this may imply that saltmarshes are especially dangerous as receiving sites for toxic waste because they may have the potential to readily move toxicants into the food web.