1. Marine Ecological Laboratory 201582170 Dabin Lee
Ammonium inhibition of nitrate uptake by phytoplankton in the Amundsen Sea, Antarctica
Marine Ecological Laboratory
Dabin Lee

2. Limiting factors influence on primary production
Most aquatic ecosystems are limited by the light, oxygen, and nutrients
Nitrogen is major limiting nutrients in the ocean environment

3. Nitrogen cycle in marine ecosystem
Ammonium (NH4+) formed by N-fixation and Decomposition of organisms
Primary production based on NO3- and NH4+ called as ‘new production’ and ‘regenerated production’

4. New and regenerated production
New primary production = Total primary production – regenerated production
New production contribute to export of production

5. Interaction between ammonium and nitrate uptake
No nitrate uptake above a threshold ammonium concentration (R. Dugdale et al., 2012)
Small amounts of ammonium may stimulate nitrate uptake (Q Dortch, 1990)
Evidence for the negative effect of ammonium (Q Dortch, 1990) 1) Laboratory studies (reviewed in Morris 1974) 2) Early field studies 3) Theoretical considerations
NH4+
Concentration-dependent NH4+ uptake
Inhibition of NO3- uptake
Stimulation of NO3- uptake

6. Nitrate uptake in the HNLC regions
The low rates of nitrate (NO3-) uptake in the Southern Ocean and other HNLC regions ; have often been explained by ammonium inhibition of NO3- utilization (Smith and Nelson, 1990; Wheeler and Kokkinakis, 1990; Price et al., 1994)

7. Objective 1
Define the relationship between nitrate and ammonium in the Amundsen Sea 2
Find the threshold ammonium concentration that can inhibit nitrate uptake 3
Quantify the inhibition effects of ammonium on nitrate uptake by phytoplankton

8. Study Area
Regional comparison; open water, marginal ice zone, polynya, ice shelf

9. Method
1L polycarbonate bottle
control
1 μM
2 μM
3 μM
5 μM
10 μM
100%
30% 1%
Ammonium gradient
All samples enriched with stable isotope tracer (13C + 15NO3)

10. Method Isotope ratio mass spectrometry 25mm GF/F filter paper
Incubated samples
47mm GF/F filter paper
High performance liquid chromatography

11. Expected results Nitrogenous nutrients utilization shifting
C. Tungaraza et al. (2003)
Nitrogenous nutrients utilization shifting
Shift patterns according to community structure
Predict the change of community structure by climate change
W.P. Cochlan and D.A. Bronk (2003)

12. Thank you!