Biogeosciences Discussions www.biogeosciences-discuss.net 1810-6277 1810-6285 6 4 2009 10.5194/bgd-6-7175-2009 http://www.biogeosciences-discuss.net/6/7175/2009/ http://www.biogeosciences-discuss.net/6/7175/2009/bgd-6-7175-2009.html http://www.biogeosciences-discuss.net/6/7175/2009/bgd-6-7175-2009.pdf 7175 7205 2009-07-17 Effects of an iron-light co-limitation on the elemental composition (Si, C, N) of the marine diatoms <i>Thalassiosira oceanica</i> and <i>Ditylum brightwellii</i> E. Bucciarelli eva.bucciarelli@univ-brest.fr P. Pondaven G. Sarthou Université Européenne de Bretagne, France Université de Brest, CNRS, IRD, UMR 6539 LEMAR, IUEM; Technopôle Brest Iroise, Place Nicolas Corpernic, 29280 Plouzané, France 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, <i>Thalassiosira oceanica</i> and <i>Ditylum brightwellii</i>. 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 (<i>T. oceanica</i>, Fe-L co-limitation), no change (<i>T. oceanica</i>, Fe limitation) and a decrease (<i>D. brightwellii</i>, 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:μ_max) 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. 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