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

Abstract

Emergent macrophytes are a major source of organic matter production in freshwater wetlands, and often represent the bulk of the plant material entering the detrital pool. We examined the decomposition and microbial dynamics associated with litter of the emergent macrophyte, Juncus effusus (soft rush), during its movement from an aerial standing dead to a submerged decay environment. Standing dead leaves of J. effusus were collected after an initial period of standing litter microbial decay, placed in 1-mm mesh litter bags, and submerged in a wetland. Litter bags were retrieved periodically over 268 d and analyzed for microbial (fungal and bacterial) biomass and production, ATP concentrations, litter mass loss, and quality (C: N: P and plant fiber). Submerged litter decay of J. effusus was slow (k 5 0.0010 d21), with only 23 % weight loss after 268 d. Both fungal and bacterial biomass and production decreased significantly soon after standing plant litter was submerged in the wetland surface waters. Despite de-creases in microbial biomass and production, fungal decomposers remained the dominant microbial assemblage associated with decaying plant litter, accounting for 99 % and 91 % of the total microbial biomass and production, respectively. Mean fungal production ranged from 73–2,836 mg C g21 AFDM d21 (AFDM: ash-free dry mass remaining) during the study period, whereas attached bacterial production ranged from 4–32 mg C g21 AFDM d21. Patterns of litter ATP and nutrient concentrations (N and P) were similar to those observed for fungal and bacteria