Water potential of standing-dead shoots of an intertidal grass.

Dead stems and leaves of smooth cordgrass (Spartina alterniflora Loisel.) undergo substantial fungal decay in the standing position. We conducted a series of experiments to determine the probable range of water availabilities that cordgrass-fungal decomposers experience; we determined the effects of duration of wetting and drying, site on shoots, leaching of osmotica, and stage of decomposition on water potential (ψ) of cordgrass shoots. Dried pieces of cordgrass shoots took up water rapidly when submerged, rising from values which were probably less than -150 megapascals (MPa) water potential to about -3.5 (soaked in seawater) or -1.5 (soaked in tapwater) within 5 min. Air-drying resulted in a return to low ψ (<-7.5 MPa) within an hour. Literature reports show that most litter and wood-decomposing fungi which have been tested cannot grow at ψ more negative than -6 MPa. The more lignified stems showed a more negative matric ψ than leaves at water contents greater than 25% fresh weight. As leaves decomposed in the marsh, their ψ increased (from -1.7 to -0.5 MPa, under standard conditions of 30 min freshwater soaking and 30 min air-drying), similar to what other investigators have found for wheat and forest litter. The water content at which cordgrass leaves reached -6 MPa was about 23% fresh weight, within the range (15-32%) found for wheat straw and forest litter.