CYCLING OF MARINE DISSOLVED ORGANIC-MATTER .2. A MODEL ANALYSIS

Nutrient pathways within the microbial food web were analysed using a mechanistic model based on a multi-stage flow-through experimental sys tem. Good agreement with measured values reflected the model's ability to function on 3 different orders of magnitude with respect to turnov er time. Important observations made from the experimental system incl uded the production of viruses, the presence of dead bacterial cells ( ghosts), and the production of detritus. This led to the concept that the bacterial community forms a continuum from Live uninfected cells t hrough infected cells, dead cells, degraded cells (detritus) and ends in dissolved organic matter. Enzymatic degradation of dissolved organi c matter was balanced by its release during cell lysis caused by virus es, predation by flagellates, and degradation of detritus. This formed 3 closed loops in the model for nutrient recycling. Simulations predi cted that phosphorus recycling occurred via nucleic acids released dur ing cell lysis caused by viruses and that nitrogen was recycled via pr oteins released as a combined result of cell lysis caused by viruses, predation by flagellates, and degradation of detritus. This implies th at for natural ecosystems, the availability of nitrogen, phosphorus, a nd carbon species for bacterial growth can be dominated by internal re cycling, depending on the molecular species in question and the turnov er time. Different nutrients are made available by different processes of recycling which potentially occur on different time scales.