Microbial dynamics associated with leaves decomposing in the mainstem and floodplain pond of a large river

Abstract

Aquatic habitats of forested floodplain systems receive large inputs of allochthonous plant litter. We examined the decomposition of, and microbial productivity associated with, leaves of a common floodplain tree, Populus gr. nigra, in the mainstem and floodplain pond of a seventh order river in 2 consecutive years. Litter bags were submerged at both sites, retrieved periodically, and analyzed for litter mass loss, bacterial and fungal biomass, growth rate and production, and sporulation rates of aquatic hyphomycetes. Litter decomposition rates were similar in both sites and years (leaf breakdown coefficients k of 0.0070 to 0.0085 d -1 ), although microbial dynamics partly differed between sites. Species diversity of aquatic hyphomycetes was lower on leaves submerged in the pond (16 species) than in the river (21 species). Mycelial biomass was also significantly lower in the pond, with values < 20 mg C g -1 of detrital C, whereas peaks of 50 and 80 mg C g -1 were reached in leaves in the mainstem. These differences contrast with the comparable fungal productivity at both sites (peak rates of 1.4 mg of mycelial C per g of detrital C per day in both years). This suggests that fungi were equally productive in both habitats but experienced greater losses in the pond. Bacterial numbers and biomass also showed the same basic pattern at both sites, although somewhat higher levels were reached in the pond (maximum of about 10 10 cells and 0.5 mg g -1 of detrital C). Bacterialspecific production rates fluctuated between 0.06 and 1.5 d -1 with lower values occurring in the floodplain pond. Although bacteria on leaves were clearly outweighed by fungi in terms of biomass, they accounted for a sizeable fraction of the total biomass (up to 11%), and up to 32% of the total microbial production. Our comparison of bacterial and fungal productivity thus points to a critical role of fungi in litter decomposition in aquatic habitats of river floodplain systems, while suggesting that bacteria must not be overlooked as important agents of litter decompositon in riverine environments.KEY WORDS: Fungi · Bacteria · Leaf litter · River · Floodplain · Decomposition · Microbial production Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 28: [25][26][27][28][29][30][31][32][33][34][35][36] 2002 persistence, water quality (e.g. temperature, turbidity, chemical composition), sediment grain size distribution and organic matter content, and hence in biological characteristics (Tockner et al. 1999).A salient feature of river floodplain forests is their high primary productivity (Naiman & Decamps 1997). It results in large inputs of litter to both the forest floor and a range of lentic and lotic water bodies. A large portion of these inputs occurs in the form of autumnshed leaves from the riparian vegetation (Chauvet & Jean-Louis 1988, Cuffney 1988, suggesting that leaf decomposition constitutes a vital process in floodplain river systems (Chauvet 1988, Chergui & Pattee 1990, McArthur et...

Diversity of Fungi, Bacteria, and Actinomycetes on Leaves Decomposing in a Stream

“…Overall, bacterial biomass values obtained in our study were comparable to those in other studies (2,14,70). In a study by Baldy et al (1), the greatest bacterial biomass was observed on leaves of the London plane tree (Platanus hybrida), the species with the slowest breakdown rate in their study.…”

“…In addition, variability of bacterial biomass on sugar maple leaves suggests that as it decays, it can provide a more dynamic and variable environment than oak leaves. We observed greater fungal biomass than bacterial biomass throughout our study, as has been reported by others (2,14,21,70). Greater fungal biomass likely occurs because fungi are more efficient than bacteria (except for a few tunneling bacteria [10,49,69]) in exploiting available resources through invasion and enzymatic hydrolysis of leaf material and lysed hyphae (9,56).…”

“…Yet, in spite of these differences in decomposition and known differences in leaf chemistry (47), few differences in the microbial community were detected between the leaf species. For example, fungal biomass did not differ between the leaf types, although peak fungal biomass estimates were within the range of values reported in the literature for leaves in streams (2,14,70).…”

“…This hypothesis is supported by the correlation between fungal and bacterial biomass we observed. Biomass estimations reported here for fungi and bacteria are based on different methods, following the approach of earlier studies (1,2), suggesting that direct comparisons of the two groups be made with caution. For bacteria, conversion of biovolume to biomass via allometric or linear conversion factors (51) was utilized, but this is not feasible for fungi.…”

“…Yet, most studies of leaf decomposition in streams provide no information on the diversity of bacteria (1,2), focusing solely on fungi (21,28). In some studies, the aquatic hyphomycete species are listed (2,70), but for bacteria, generally total numbers, biomass, or production rates are reported without information on the taxa present (1,2,23,63).…”