Lomas, M. W. University of Maryland Center for Environmental Science, lomas@hpl.umces.edu
Rumbley, C. W. Salisbury State University,
Glibert, P. M. University of Maryland Center for Environmental Science, glibert@hpl.umces.edu

 
NITROGEN RELEASE BY MARINE PHYTOPLANKTON UNDER LIGHT STRESS: COMPARISON OF SPECIES
 
Marine diatoms commonly form large blooms during periods of cool temperatures, high nitrate concentrations and turbulent mixing, but the physiological adaptations which allow diatoms to bloom under these conditions are not well understood. We have previously suggested that under temperature or light stress diatoms may dissipate excess photochemical energy by non-assimilative nitrate reduction followed by nitrogen release. Here we tested this in the lab by comparing the fate of a pulse of nitrate in 3 diatoms (Chaetoceros spp., Skeletonema costatum, Thalassiosira weissflogii) and 3 flagellates (Dunaliella tertiolecta, Monochrysis lutheri, Prorocentrum minimum) each exponentially grown at 4 temperatures (4-20C), and each exposed to 2 irradiance levels. At all growth temperatures, diatoms released on average 3% of the nitrate as ammonium at the growth irradiance and 120% at the elevated irradiance level. Diatoms also released 2.4-3.1% as nitrite at the 2 irradiance levels, respectively. In contrast, the flagellates released <10% of the nitrate pulse as either nitrite or ammonium, and, in fact, demonstrated net uptake rates of ammonium under all conditions. Nitrogen metabolism in diatoms thus differs substantially from those of flagellates under light stress conditions and may involve the use of nitrate in non-nutritional pathways.
 
Day: Thursday, Feb. 4
Time: 09:00 - 09:15am
Location: Sweeney Center
 
Code: CS62TH0900S