Seasonal changes in fungal production and biomass on standing dead Scirpus lacustris litter in a northern prairie wetland.

Decaying macrophytes are an important source of carbon and nutrients in fungal and bacterial communities of northern prairie wetlands. Dead macrophytes do not collapse into the water column immediately after death, and decomposition by fungi and bacteria begins while the plants are standing. The seasonal variations in fungal biomass and production on Scirpus lacustris stems, both above and below water, were measured to assess which environmental factors were dominant in affecting these variations in a typical prairie wetland. Fungal biomass and production were measured from early May to November, just prior to freeze-up. Fungal decomposition began and was greatest in the spring despite low water temperatures. The fungal production, as measured by the incorporation of [1-(14)C]acetate into ergosterol, ranged from 1.8 to 376 microg of C g of ash-free dry mass (AFDM)(-1) day(-1), and the biomass, as estimated by using ergosterol, ranged from nondetectable to 5.8 mg of C g of AFDM(-1). There was no significant difference in biomass or production between aerial and submerged portions of Scirpus stems. The water temperature was correlated with fungal production (r = 0.7, P < 0.005) for aerial stem pieces but not for submerged pieces. However, in laboratory experiments water temperature had a measurable effect on both biomass and production in submerged stem pieces. Changes in fungal biomass and productivity on freshly cut green Scirpus stems decaying in the water either exposed to natural solar radiation or protected from UV radiation were monitored over the summer. There was no significant difference in either fungal biomass (P = 0.76) or production (P = 0.96) between the two light treatments. The fungal biomass and rates of production were within the lower range of the values reported elsewhere, probably as a result of the colder climate and perhaps the lower lability of Scirpus stems compared to the labilities of the leaves and different macrophytes examined in other studies performed at lower latitudes.