QUANTITATIVE CATION REQUIREMENTS OF SEVERAL GREEN AND BLUE-GREEN ALGAE(2).

In contrast with studies which have based essential element requirements of algae on nutrient solution concentrations, in this investigation the requirements of each of 6 species of green and blue-green algae for calcium, magnesium, and potossium were quantitatively evaluated in terms of critical cell concentrations of the 3 cations. A critical cell concentration was considered the minimum cell content of an element which permitted maximum or near maximum total growth of an organism. In comparison with the needs of angiosperm crop plants, the requirements of all 6 species for calcium were extremely low (critical cell contents of 0.06% or less, oven-dry basis); requirements for magnesium were equal to or only slightly less than in higher plants (0.15-0.30%) with the exception of Scenedesmus quadricauda (0.05%); and the requirements for potassium varied greatly, from critical levels less than the average values established for higher plants (0.25-0.50%) to values equal to or in excess of higher plant averages (0.80-2.40%). The nutrition of S. quadricauda was of particular interest because of extremely low requirements for all 3 cations. The results provide a more precise and meaningful expression of the essential cation requirements of algae than have previous data. The results also suggest differences in the physiology and functions of cations in the algae studied and in angiosperms which seem worthy of further investigation.