Adams, T. S. University of Minnesota, adam0100@tc.umn.edu
Sterner, R. W. University of Minnesota, stern007@tc.umn.edu

 
THE EFFECT OF DIETARY NITROGEN CONTENT ON DEL 15N ENRICHMENT ACROSS TROPHIC LEVELS
 
We investigated the relationship between the del 15N of the anomopod crustacean, Daphnia magna, and the C:N of the green alga, Scenedesmus acutus. We hypothesized that as dietary nitrogen increased (decreasing C:N), organismal del 15N would increase due to preferential excretion of 14N coupled with increased nitrogen availability. Daphnids were raised on three types of S. acutus which ranged in C:N (atomic) from 7.34 to 24.76. Del 15N enrichment was found to be strongly linearly related to the C:N of the algae, ranging from nearly zero to approximately 6 per mil. The del 15N values of the daphnids as well as the discrimination (animal del 15N - algae del 15N), were inversely correlated to the nitrogen content of the algae. The observed trend runs counter to our hypothesis and may result from a number of possible causes. Nitrogen conservation, causing increased internal nitrogen recycling under nitrogen limited conditions may result in the observed increase in daphnid del 15N with decreased dietary nitrogen. Additionally, the del 15N of D. magna may increase with increasing organismal size, age, and /or egg production. Finally, microbial ingestion and assimilation by D. magna may effect the overall organismal del 15N.
 
Day: Tuesday, Feb. 2
Time:
Location: Sweeney Center
 
Code: SS32TU0142S