Microbial biomass, growth, and respiration associated with submerged litter of Phragmites australis decomposing in a littoral reed stand of a large lake

This study examined the microbial dynamics associated with decomposing litt er of the widespread emergent macrophyte Phragmites australis in a Littoral reed stand of a large lake. Standing dead leaf and stem litter were collec ted, placed into fine and coarse mesh litter bags, and submerged in the ree d stand. Litter bags were retrieved periodically and analyzed for fungal an d bacterial biomass, fungal growth rates and production, rates of microbial respiration, litter mass loss, nutrient concentrations (N and P), and rate s of dissolved organic carbon (DOC) release. Microbial biomass associated w ith both leaf and stem litter (12 to 85 mg C g(-1) detrital C) was predomin antly fungal (always greater than or equal to 90 % of the total biomass), e ven though bacterial biomass (0.13 to 5.6 mg C g(-1) detrital C) increased and fungal biomass decreased or remained constant as litter decay proceeded . Although rates of fungal growth (0.02 to 0.08% h(-1)) and production (lea ves only; 3 to 51 mug C g(-1) detrital C h(-1)), and rates of microbial res piration (11 to 257 mug C g(-1) detrital C h(-1)) decreased following litte r submergence, fungi continued to be metabolically active in both leaf and stem litter. Significant differences in fungal and bacterial biomass, funga l production rates, and rates of respiration were observed between leaf and stem material, with leaves often having 5 times higher values than corresp onding stems. Rates of mass loss differed significantly between leaf Litter in fine and coarse mesh bags, with less than 10% of the initial mass remai ning in coarse mesh bags after 86 d, versus nearly 60 % remaining in fine m esh bags. Nitrogen and P concentrations of leaf litter enclosed in fine mes h bags increased during litter decay, whereas N concentrations of leaf litt er in coarse mesh bags remained unchanged and P concentrations decreased. B oth N and P concentrations of stem litter were similar among litter bags an d varied little throughout the study period. Results obtained in this study indicate that significant changes in microbial colonization and activity a ssociated with P, australis litter can occur following the collapse of stan ding dead plant matter to the water. Furthermore these findings suggest tha t fungi are active on submerged litter and thus play a vital role in the de composition of P. australis litter in the aquatic environment.