| In streams, bacteria play an important role in the decomposition of leaf litter and the utilization of dissolved organic carbon (DOC) released from leaves. However, little is known about the taxonomic composition of the bacterial community. The purpose of this study was to determine patterns of change in the number of bacteria at different taxonomic levels in biofilms on the surface of decomposing maple leaves. Additionally, artificial substrata experiments were used to determine bacterial response to leachate from leaves at different stages of decomposition. The number of cells in the Domain Bacteria, the alpha-, beta-, and gamma-proteobacteria, and three species of bacteria (Acinetobacter calcoaceticus, Burkholderia cepacia, and Pseudomonas putida ) were enumerated using epifluorescence microscopy after in situ hybridization with fluorescently labeled oligonucleotides. The proteobacterial groups made up 63–67% of the Domain Bacteria. The alpha-proteobacteria generally made up the largest percentage of the Domain Bacteria each year while the gamma-proteobacteria group was smallest, and the beta-proteobacteria fluctuated, making up a larger percentage in some years than others. The population sizes of the bacterial species exhibited different patterns of change in density in the biofilm. Relative to the other two species, the A. calcoaceticus population size in the biofilm was low, B. cepacia and P. putida reached maximum population sizes at different times in biofilm formation. A. calcoaceticus did not respond to any of the leachate treatments in the artificial substrata experiment. B. cepacia and P. putida reached the largest population size on leachate corresponding to the period of time in which the maximum population size was observed in the leaf biofilm. DOC released from the leaves influenced bacterial populations on the leaf surface, but not all taxonomic groups were effected in the same manner. A. calcoaceticus was unaffected by DOC from the leaves, while response to components of the DOC (e.g., phenolics) strongly influenced population densities of B. cepacia and P. putida. |
