Publication Date:
2009-07-17
Description:
We examined the effect of iron (Fe) and Fe-light (Fe-L) co-limitation on cellular silica (BSi), carbon (C) and nitrogen (N) in two marine diatom species, Thalassiosira oceanica and Ditylum brightwellii. We showed that C and N per cell tend to decrease with increasing Fe and Fe-L co-limitation (i.e. decreasing growth rate). We observed an increase (T. oceanica, Fe-L co-limitation), no change (T. oceanica, Fe limitation) and a decrease (D. brightwellii, Fe and Fe-L limitations) in BSi per cell with increasing degree of limitation. When comparing our results to literature data, we noted that the trend in C and N per cell for other Fe limited diatoms was similar to ours. However there was no global trend in BSi, which suggests interspecific differences. The relative variations in C:N, Si:C and Si:N versus the relative variation in specific growth rate (i.e. μ:μmax) followed the same patterns for both species under Fe and Fe-L co-limitation. The variations of C:N under Fe limitation reported in the literature for other diatoms are contrasted, which may thus be more related to growth conditions than to interspecific differences. Si:C and Si:N ratios increased by more than 2-fold between 100% and 40% of μmax. Under more severe limitation (Fe or Fe-L), these ratios tend to decrease. To asses the field significance of our results, we compared them to those of artificial Fe fertilisation experiments. This comparison showed that Si:N increased between 100% and ~40% of μmax, but decreased between 40% and 20% of μmax, and increased again below 20% of μmax. Between ~15% and 30% of μmax, Si:N was even lower than under non limiting conditions. These results may have important biogeochemical implications on the understanding and the modeling of the oceanic biogeochemical cycles, e.g. carbon export.
Print ISSN:
1810-6277
Electronic ISSN:
1810-6285
Topics:
Biology
,
Geosciences
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