Effects of iron on the elemental stoichiometry during EIFEX and in the diatoms <i>Fragilariopsis kerguelensis</i> and <i>Chaetoceros dichaeta</i>
The interaction between iron availability and the phytoplankton elemental composition was investigated during the in situ iron fertilization experiment EIFEX and in laboratory experiments with the Southern Ocean diatom species <i>Fragilariopsis kerguelensis</i> and <i>Chaetoceros d...
Main Authors: | , , |
---|---|
Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2007-08-01
|
Series: | Biogeosciences |
Online Access: | http://www.biogeosciences.net/4/569/2007/bg-4-569-2007.pdf |
Summary: | The interaction between iron availability and the phytoplankton elemental composition was investigated during the in situ iron fertilization experiment EIFEX and in laboratory experiments with the Southern Ocean diatom species <i>Fragilariopsis kerguelensis</i> and <i>Chaetoceros dichaeta</i>. Contrary to other in situ iron fertilization experiments we observed an increase in the BSi:POC, BSi:PON, and BSi:POP ratios within the iron fertilized patch during EIFEX. This is possibly caused by a relatively stronger increase in diatom abundance compared to other phytoplankton groups and does not necessarily represent the amount of silicification of single diatom cells. In laboratory experiments with <i>F. kerguelensis</i> and <i>C. dichaeta</i> no changes in the POC:PON, PON:POP, and POC:POP ratios were found with changing iron availability in both species. BSi:POC, BSi:PON, and BSi:POP ratios were significantly lower in the high iron treatments compared to the controls. In <i>F. kerguelensis</i> this was caused by a decrease in cellular BSi concentrations and therefore possibly less silicification. In <i>C. dichaeta</i> no change in cellular BSi concentration was found. Here lower BSi:POC, BSi:PON, and BSi:POP ratios were caused by an increase in cellular C, N, and P under high iron conditions. These results indicate that iron limitation does not always increase silicification in diatoms and that changes in the BSi:POC, BSi:PON, and BSi:POP ratios under iron fertilization in the field are caused by a variety of different mechanisms. Our results therefore imply that simple cause-and-effect relationships are not always applicable for modeling of elemental ratios. |
---|---|
ISSN: | 1726-4170 1726-4189 |