Si uptake ratio during Fe-limited or Fe-unlimited (Research Introduction)
Topic outline
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The difference in Si uptake ratio between Fe-restricted and Fe-unrestricted (Research Introduction)（Takeda S, Nature, 1998）
Phytoplankton requires macronutrients (N, P, Si) as well as micronutrients such as iron for growth. There are areas, such as the Bering Sea, where macronutrients are abundant but the corresponding biological production is not. In these places, production may be limited due to a lack of the micronutrient iron (iron limitation).
Introduction of a study of changes in the Si uptake ratio by diatoms in Fe-restricted or Fe-unrestricted（Takeda S, Nature, 1998）
The nutrients uptake ratio by diatoms under sufficient iron (iron unrestricted) conditions were as follows (A)
Nutrient uptake ratio of diatoms N:P:Si = 12 : 1 : 14 (A)
Nutrient uptake ratios under iron-deficient (iron-limited) conditions were (B)
Nutrient uptake ratio of diatoms N:P:Si = 12 : 1 : 31 (B)
Under conditions of sufficient iron and suitable for growth, the Si / P uptake ratio was 14, and under iron-deficient and growth-limited conditions, the Si / P uptake ratio was 31, indicating a higher uptake of Si.
Iron deficiency causes diatoms to thicken their siliceous shells and increase their Si uptake ratio. When iron and nutrients (N, P) are sufficient, diatoms divide and proliferate one after another without time to thicken their diatom shells, resulting in a low Si uptake ratio. The N/P ratio by diatoms is 12, which is much lower than the Redfield ratio (16). This is thought to be because diatoms in good nutritional condition store more lipids (high P ratio) in their bodies.
Below is an image that illustrates the difference in diatom shell thickness between well and poorly-nourished diatoms. If the nutritional condition is good, the silica shell becomes thinner through successive cell division, and the Si uptake ratio becomes smaller. If the nutritional condition is poor, cell division is not possible. In such a case, the silica armor will be thickened to protect itself, and the Si uptake ratio will increase (Pondaven et al., 2006). (Interpreted by Pondaven et al., Protist, (2007))
珪藻細胞： Diatom cell 栄養状態が良ければ、次々と細胞分裂： Cell division occurs one after another under good nutritional conditions 栄養状態が悪いと、細胞分裂ができず、殻を分厚くするしかない： Difficult for cell division and thickens cell under poor nutritional conditions
海洋の栄養状態と珪藻によるケイ素取り込み比率の関係： Relationship between the nutrient status of the ocean and the Si uptake ratio by diatoms
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