| Dissolved organic nitrogen (DON) comprises a large fraction of dissolved nitrogen in marine environments. The basic premise of this research is the DON pool is composed of a large number of compounds, and though flux rates of any single DON compound may be small, taken together they represent a significant flux of nitrogen in marine systems. The objectives of this dissertation were to develop methods to quantify rates of DON release by phytoplankton and subsequent microbial uptake of DON. Methods were developed to measure DON release and uptake using ;Rates of DON release vary as a function of the form of inorganic nitrogen utilized, NH;Rates of DON release vary as a function of the organisms present. In a 36 h experiment with size fractionated Choptank River water enclosed in large carboys, release rates of DON were much higher in the ;Rates of release also vary as a function of nitrogen sufficiency. In a study with two clones of the cyanobacterium, Synechococcus, grown in batch culture, rates of low molecular weight (LMW) DON release were higher during nitrogen starved growth than during exponential growth.;Two studies in Chesapeake Bay demonstrated that recently released DON is taken up by the microbial community. In May, during the decline of the spring bloom, rates of DON uptake exceeded uptake rates of NH... |
