Effect of zinc availability on the morphology and nutrient physiology of a coastal and an oceanic diatom




Willers, Valeria

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Low dissolved zinc concentrations in marine waters can limit growth and productivity of phytoplankton. as Zn is a required component of critical enzymes such as carbonic anhydrase. This thesis examined the effects of Zn availability on growth rates. cell morphology, elemental composition and ratios, and incorporation rates of macronutrients in the coastal diatom Skeletonema costatum and the oceanic diatom Thalassiosira oceanica. Under Zn limitation. S. costatum exhibited a decrease in maximum growth rate (60%), chlorophyll content (20%) and an increase in the surface to volume (S/V) ratio (80%) compared to Zn-replete cells. In S. costatum elemental quotas showed a decrease in silicon content (20%) and a significant increase in carbon content (52%) and phosphorus content (55%). Moreover. silicon content per surface area significantly decreased by 50% under Zn limitation. Elemental ratios showed significant differences only for Si:C and Si:N between Zn-replete and Zn limiting conditions. The elemental stoichiometry of S. costatum was 82C : 9N : 5Si : 1P under Zn-limiting conditions compare to 84C : 12N : 9Si : 1 P under Zn-replenishment. In T oceanica. Zn limitation was also responsible for a decrease in maximum growth rate (60%) and chlorophyll content (20%) compared to Zn-replete cells, but Zn limitation did not affect the S/V ratio. Elemental quotas and ratios in T. oceanica did not exhibit significant differences under Zn limitation. However. nitrogen. silicon and phosphorus content showed a 20% increasing trend in Zn-limited cells. Elemental quotas for T. oceanica were 51C : 6N : 2Si : 1P under Zn-limitation and 71C : 6N : 2Si : 1P under Zn-replenishment. These laboratory experiments suggest that Zn availability in the oceans can affect the stoichiometry of nutrient uptake and the structure of phytoplankton assemblages. especially in coastal environments.



Diatoms, Zinc