Iron reduction and micronutrient nutrition of juvenile Macrocystis pyrifera (L.) C. A. Agardh (giant kelp) were investigated using a chemically defined artificial seawater medium, Aquil. Juvenile sporophytes were grown and Aquil formulations were prepared in a Class 1000 cleanroom. Weights of the juveniles at the beginning and end of experiments determined the success of the various Aquil formulations.
Micronutrient experiments showed that kelp store surprisingly large quantities of Fe, Mn, Cu, Zn, Mo, Co and I, enough for 20- to 30-fold increases in weight. A maximum growth rate of 0.38 per day was measured for juvenile Macrocystis grown in Aquil. X-ray fluorescence analysis of dried, pressed blades determined kelp tissue element concentrations.
Kelp grew fastest with 250 nM Fe, 5 nM Mn, 100 nM Zn, 1000 tiM No and 300 mM Co. Concentrations of iodine up to 500 nM I- and of copper up to 500 nM produced neither stimulating nor inhibitory responses. Theoretical chemical species concentrations in Aquil formulations were calculated using the thermodynamic equilibrium computer program REDEQL2.
Kelp reduced Fe(III) to Fe(II) supporting the hypothesis that prior to uptake, iron is reduced in and then dissociates from the chelate complex, Fe-EDTA. This mediation was enhanced by the presence of light. The effects of photoreduction alone on Fe(III) reduction were studied, establishing its minor contribution as a source of Fe(II).
