Microbial biomass and production associated with decaying leaf litter of the emergent macrophyte Juncus effusus

Emergent macrophytes are a major source of organic matter production in fre shwater wetlands, and often represent the bulk of the plant material enteri ng the detrital pool. We examined the decomposition and microbial dynamics associated with litter of the emergent macrophyte, Juncus effusus (soft rus h), during its movement from an aerial standing dead to a submerged decay e nvironment. Standing dead leaves of J. effusus were collected after an init ial period of standing litter microbial decay, placed in 1-mm mesh litter b ags, and submerged in a wetland. Litter bags were retrieved periodically ov er 268 d and analyzed for microbial (fungal and bacterial) biomass and prod uction, ATP concentrations, litter mass loss, and quality (C:N:P and plant fiber). Submerged litter decay of J, effusus was slow (k = 0.0010 d(-1)), w ith only 23% weight loss after 268 d. Both fungal and bacterial biomass and production decreased significantly soon after standing plant litter was su bmerged in the wetland surface waters. Despite decreases in microbial bioma ss and production, fungal decomposers remained the dominant microbial assem blage associated with decaying plant litter, accounting for 99% and 91% of the total microbial biomass and production, respectively. Mean fungal produ ction ranged from 73-2,836 mu g C g(-1) AFDM d(-1) (AFDM: ash-free dry mass remaining) during the study period, whereas attached bacterial production ranged from 4-32 mu g C g(-1) AEDM d(-1). patterns of litter ATP and nutrie nt concentrations (N and P) were similar to those observed for fungal and b acterial biomass, suggesting that at least a portion of the detrital N and P may have been incorporated into microbial biomass. Significant changes in microbial colonization and activity associated with emergent macrophyte li tter can occur following the collapse of standing dead plant matter to the water or surface sediments. Furthermore, our findings suggest that fungi ar e significant contributors to the decay of coarse particulate plant matter in wetland ecosystems.