Atmospheric inputs of dissolved organic nitrogen stimulate estuarine bacteria and phytoplankton

摘要

Atmospheric deposition is recognized as a poten- tially large source of inorganic nuirients to many ecosystems. In marine systems, where nitrogen (N) is the nutrient typically limiting phytoplankton growth, rainwater is often a sigmficant source of N. Although a considerable portion of atmospheric N deposition is in the form of organic N, only the inorganic N in rainwater has been considered by most previous studies. Laboratory experiments presented here indicate that dissolved organic nitrogen (DON) from rainwater can stimulate produc- tivity of coastal marine bacteria and phytoplankton. A large percent of rainwater DON was potentially biologically avail- able; 45-75 was rapidly utilized by the microorganisms. The magnitude of the response of bacterial and phytoplankton bio- mass to equivalent amounts of DON-N or ammonium-N was similar However, the community composition of phytoplank- ton at the end of the exporiment differed in treatments receiv- ing DON and inorgamc N. Diatoms and dinoflagellates ac- counted for >90 of the phytoplankion biomass in treatments receiving rainwater DON. In contrast, small(<2 mu m) monads accounted for >85 of the biomass in the treatments receiv- ing ammonium. The results indicate that DON in rainwater can be an important souroe of N to ecosystems.