Release and bioavailability of dissolved organic matter from floodplain litter: influence of origin and oxygen levels

1. We determined the rate of release and microbial uptake of dissolved orga nic carbon (DOC) leached from three components (leaves, bark and twigs) of river red gum (Eucalyptus camaldulensis) forest litter originating from dif ferent parts of a floodplain and under different oxygen levels. 2. Preliminary experiments showed that substantially more DOC was released from leaves than from bark or twigs; there was relatively little DOC releas e from coarse particulate matter or soil. 3. Both the amount of DOC released from each litter component and the amoun t metabolized by the microbial community were independent of position on th e floodplain or amount of oxygen available to microbes. 4. Although the bioavailability of DOC was independent of oxygen concentrat ion, the microbial utilization of DOC under aerobic and anaerobic condition s differed. Under aerobic conditions, leaves were colonized by fungi, while bacteria were dominant under anoxic conditions. 5. Phospholipid fatty acid profiles of the microbial communities growing on leaf extracts showed that different microbial communities developed in eac h oxygen concentration treatment suggesting that, irrespective of flood con ditions, a microbial community will develop to utilize a significant propor tion of the DOC leached from litter.