Multiyear patterns of fungal biomass dynamics and productivity within naturally decaying smooth cordgrass shoots

Ascomycetous fungi are predominant secondary microbial producers of the smooth cordgrass (Spartina alterniflora ) shoot decay system. A 3-yr examination of concentrations of living fungal mass (as ergosterol content) in naturally decaying cordgrass, and of instantaneous rates of cordgrass‐fungal production (as rates of incorporation of radiolabeled acetate into ergosterol at a standard temperature of 20 8C), was conducted in three salt-marsh watersheds of Sapelo Island. Though the years of study were climatologically different (e.g., rainfall ranging over a factor ;2), ergosterol content of decaying leaves was not different from year to year, with a grand mean of 371 mg ergosterol g 21 organic mass of decaying system, and there was little difference among yearly average fungal productivities (range 5 155‐217 mg fungal organic mass g 21 system organic mass h 21 for autumn‐spring data). Significant differences in ergosterol content of decaying leaves were found among marsh watersheds, probably due to differences in nitrogen (but not phosphorus) availability, but these were not large (maximum 1.3-fold for multiseasonal data), and differences were not found among marsh subsites (short to tall shoot) nor, for the most part, among types or parts of decaying leaves. Season of sampling, however, had a large effect upon fungal biomass and fungal productivity: average ergosterol contents were significantly higher in winter and spring (e.g., 416‐554 mg g 21 organic mass of decaying blades) than in summer or autumn (,310 m gg 21 ). Among the potential reasons for this unexpected pattern of seasonality might be (1) greater access of mycophagous invertebrates and/or bacterial competitors due to higher tides and lower elevation of leaves in late summer and fall, and (2) leaching of leaf digestate during periods of high rainfall and high spring tides. Significant correlations were found between ergosterol content of decaying leaves and mean tidal height for the 3 months before sampling (r 52 0.77) and for fungal productivities and 3-month rainfall (r 52 0.62). Grazing of decaying leaves by salt-marsh periwinkles over the range of snail densities of the study sites (0‐85 m 22 ) gave no clear evidence of depression of fungal biomass or repression of fungal activity, contrary to previous findings for higher snail densities. The calculated seasonal change in living fungal percentage of decaying leaves was from ;6 (summer‐autumn) to 9% (winter‐spring), and in 6month fungal production, the change was from 101 to 434 g organic fungal mass m 22 marsh surface. Gallagher and Pfeiffer (1977), with their publication of data for high rates of metabolism by the ‘‘dead plant community’’ on/in standing dead parts of shoots of smooth cordgrass (Spartina alterniflora), including greater retention of dissolved organic carbon when respiration rates were high, sparked interest in this formerly inert-seeming component of salt-marsh ecosystems of the southeastern U.S.A. The ‘‘dead plant community’’ consists primarily of a small group of species of ascomycetes that is invariably associated with the natural decay of leaves of smooth cordgrass, especially Phaeosphaeria spartinicola, Phaeosphaeria halima,an unnamed species of Mycosphaerella, and Buergenerula spartinae (Gessner 1977; Newell et al. 2000; Newell and Porter 2000; Newell 2001a). Lee et al. (1980) introduced measurement of fungal mass within decaying shoot material of smooth cordgrass using ergosterol as a biomass proxy. This was a major step forward, because the mass that fungi produce during marshgrass decay is located primarily within the 1