Decomposition and CO2 evolution from standing litter of the emergent macrophyte Erianthus giganteus

Decomposition of standing litter of the emergent macrophyte Erianthus giganteus (plumegrass) was quantified in a small freshwater wetland in Alabama, USA. Living green shoots off. giganteus were tagged and periodically retrieved for determination of leaf and culm mass loss, litter-associated fungal biomass (ergosterol), and nitrogen and phosphorus concentrations. Laboratory studies were also conducted to examine the effects of plant litter moisture content and temperature on rates of CO2 evolution from plant litter. Culm and leaf material lost 25 and 32% AFDM, respectively, during plant senescence and early litter decay. Fungal biomass, as determined by ergosterol concentrations, increased significantly in both leaf and culm litter during decomposition, with maximum biomass accounting for 3.7 and 6.7% of the total detrital weight in culm and leaf litter, respectively. Spatial differences in fungal biomass were observed along the culm axis, with upper regions of the culm accumulating significantly greater amounts of fungal mass than basal regions (p < 0.01, ANOVA). Rates of CO2 evolution from bath leaf and culm litter increased rapidly after wetting (0 to 76 mu g CO2-C g(-1) AFDM h(-1) within 5 min). In addition, rates of CO2 evolution from water saturated culms increased exponentially as the temperature was increased from 10 to 30 degrees C. These results provide evidence that considerable microbial colonization and mineralization of standing emergent macrophyte litter can occur before collapse of senescent shoot material to the water and sediment surface.