Document: JEN-3-74-6

Interactions between bacteria and phytoplankton affect algal response to nutrients and dissolved organic matter.

KLUG, J.*

University of Wisconsin, Madison, WI 53706, U.S.A. ¹

Abstract:
Dissolved organic matter (DOM) may affect phytoplankton growth in several ways. A major negative effect is the limitation of phytoplankton growth by shading from absorbance of light by colored DOM. However, DOM may also change the availability of inorganic nutrients directly, since it contains nitrogen and phosphorus or indirectly, by affecting bacterial processes. Bacterial degradation and respiration of DOM may change the algal availability of nitrogen, phosphorus, and carbon. I conducted short-term cubitainer experiments to explore the multiple effects of DOM on phytoplankton in West Long Lake located in Upper Michigan. When experiments were performed at low light levels, algae did not respond to additions of nutrients or DOM presumably because they were light limited. At intermediate or high light levels, algal response to added nutrients and DOM depended on the bacterial response. Mass balance calculations suggest that algae benefited when bacterial respiration of DOM prevented them from being carbon limited but were adversely affected when bacteria were able to sequester all the available phosphorus. These results suggest that algae-bacteria interactions are important for predicting the relationship between algae and DOM.

Keywords: DOM, nutrients, algae, bacteria

This abstract is being presented at: 1:30 PM in session:
Oral Session #11: Trophic Cascades.