Iron Requirement for Chlorella

Abstract

1. There are no fundamental data on the iron requirements of plants. This is true of both minimum and optimum amounts. This lack of information is due in some cases to failure to consider the solubility of the iron added to culture solutions, and in others to failure to remove completely all the iron present as impurities in such solutions. 2. We have presented a method of removing from culture solutions apparently the last traces of iron by means of adsorption at alkaline reactions, and have further shown that if sufficient sodium citrate is used in solutions free from precipitate, iron added subsequently will remain in solution indefinitely. 3. In an attempt to use these methods to determine the relation of iron to the growth of Chlorella, a high minimum concentration was found which varied in the different series, and was higher in those which had a higher sodium citrate content. 4. The hypothesis put forth in explanation of these results is that iron is active in growth only in the ionized form, and that increasing the amount of citrate decreases the ionization of the ferric citrate present in these solutions. Therefore, while we may have a larger total amount of iron present, we may have little or no growth because of a low concentration of the ferric ion. This explanation is in keeping with the work of Uspenski.