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 litter of the widespread emergent macrophyte Phragmites australis in a Littoral reed stand of a large lake. Standing dead leaf and stem litter were collected, placed into fine and coarse mesh litter bags, and submerged in the reed stand. Litter bags were retrieved periodically and analyzed for fungal and bacterial biomass, fungal growth rates and production, rates of microbial respiration, litter mass loss, nutrient concentrations (N and P), and rates of dissolved organic carbon (DOC) release. Microbial biomass associated with both leaf and stem litter (12 to 85 mg C g(-1) detrital C) was predominantly fungal (always greater than or equal to 90 % of the total biomass), even 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 (leaves only; 3 to 51 mug C g(-1) detrital C h(-1)), and rates of microbial respiration (11 to 257 mug C g(-1) detrital C h(-1)) decreased following litter submergence, fungi continued to be metabolically active in both leaf and stem litter. Significant differences in fungal and bacterial biomass, fungal production rates, and rates of respiration were observed between leaf and stem material, with leaves often having 5 times higher values than corresponding stems. Rates of mass loss differed significantly between leaf Litter in fine and coarse mesh bags, with less than 10% of the initial mass remaining in coarse mesh bags after 86 d, versus nearly 60 % remaining in fine mesh bags. Nitrogen and P concentrations of leaf litter enclosed in fine mesh bags increased during litter decay, whereas N concentrations of leaf litter in coarse mesh bags remained unchanged and P concentrations decreased. Both N and P concentrations of stem litter were similar among litter bags and varied little throughout the study period. Results obtained in this study indicate that significant changes in microbial colonization and activity associated with P, australis litter can occur following the collapse of standing dead plant matter to the water. Furthermore these findings suggest that fungi are active on submerged litter and thus play a vital role in the decomposition of P. australis litter in the aquatic environment.