Microbial Secondary Production from Salt Marsh-Grass Shoots, and Its Known and Potential Fates

Abstract

Several lines of evidence (direct microscopy, index biochemicals) point to predominance of eukaryotic decomposers in natural decay of dead shoots of smooth cordgrass (Spartina alterniflora). Recent research shows that this is also true for black needlerush (Juncus roemerianus). Ascomycetous fungi are the major initial secondary producers based on the dead shoots. There is no overlap between the species of the cordgrass (e.g., Phaeosphaeria spartinicola) and needlerush (e.g., Loratospora aestuarii) fungal-decay communities. Even when conditions in the marsh are manipulated in directions that would be expected to favor prokaryotes (extra water and nitrogen), the ascomycetes accumulate maximum organic masses in standing-decaying shoots hundreds of times larger than prokaryotic masses. Rates of fungal production are not increased by raising duration of high water availability, probably due to fine-tuned fungal adaptation to periodic dryness, but nitrogen does limit fungal productivity in decaying cordgrass. Content of living-fungal mass can be 10 to 20% of total system (= microbes + remaining plant) mass, depending on nitrogen availability, rates of invertebrate mycophagy, and probably several further factors yet to be determined. Standing crops of living fungi in cordgrass marshes in Georgia basis) have been calculated to be equal to 3% (summer) to 28% (winter) of living-cordgrass standing crop. This is calculated to be about 50 to 100% of total (non-cyano) bacterial crop; the great bulk of bacterial crop is sedimentary. Fungal productivity per standing-decaying-cordgrass marsh has been provisionally found to be 10 times greater in winter than in summer (3652 mg per per day; ). Total bacterial productivity per was calculated to be about x2 fungal in summer, and x0.07 fungal in winter. High yields of fungi (on the order of 50%) from cordgrass shoots may be part of the explanation for high rates of animal secondary production in saltmarsh ecosystems. Cordgrass-fungal standing crops and productivities (per unit leaf mass) do not show pronounced variation (in autumn) along a south-north latitudinal gradient from 30° to 44°N. One major known fate of saltmarsh-fungal secondary production is output to shredder gastropods (periwinkles, Littoraria irrorata). Other potential substantial fluxes are to 159

Benthic Bacterial and Fungal Productivity and Carbon Turnover in a Freshwater Marsh

“…12 to 15 g C m Ϫ2 year Ϫ1 ) (42,65) and standing dead plant shoots in salt marshes (535 g C m 2 year Ϫ1 ) (50). These data reveal that both bacterial and fungal production can indeed be large and that in view of the paucity of comprehensive data, the current understanding of carbon flow in nonpelagic ecosystems is correspondingly incomplete (52).…”

Autumnal Biomass and Potential Productivity of Salt Marsh Fungi from 29° to 43° North Latitude along the United States Atlantic Coast

“…Ascomycetous fungi are the principal microbial secondary producers in standing decaying salt marsh grasses (40). This conclusion has been reached by using transmission electron microscopy and direct epifluorescence microscopy and by the dynamics of a fungal index sterol, ergosterol (37,44,47).…”

The Effect of Mercury and PCBs on Organisms from Lower Trophic Levels of a Georgia Salt Marsh

“…Fungal degradation of decaying S. alterniflora shoots and shredding by invertebrates facilitates deposition on the marsh surface and availability to detritivores. Sediment bacterial biomass is comparable to that of fungal biomass, indicating that bacteria are a major component of benthic microbial productivity (Newell and Porter 1999). S. alterniflora detritus and associated microbiota provide the energetic base for saltmarsh food webs, which support a variety of meiofaunal species (Peterson et al 1985;Montague and Wiegert 1990).…”

“…High levels of primary production in southeastern U.S. salt marshes support a vigorous detrital-based food web (Montague and Wiegert 1990;Vernberg 1993;Newell and Porter 1999). Additionally, plant-derived energy can be exported from a salt marsh as dissolved organic carbon (Moran and Hodson 1994), nutrients (Turner 1993), and consumer biomass (Odum and Heald 1972;Montague and Wiegert 1990).…”

“…Primary productivity by higher plants (mostly Spartina alterniflora) is among the highest in the world (Pezeshki and DeLaune 1991). Approximately 56% of standing-decaying S. alterniflora leaf biomass is converted to fungal biomass (Newell et al 1996;Newell and Porter 1999). Fungal degradation of decaying S. alterniflora shoots and shredding by invertebrates facilitates deposition on the marsh surface and availability to detritivores.…”