SODIUM: SOME EFFECTS ON BLUEGREEN ALGAL GROWTH 1

SUMMARY The growth of heterocystous bluegreen algae in various concentrations of sodium, was examined in axenic culture as well as in situ studies. Anabaena cylindrica Lemm. with no Na + added, suffered from decreased rates of acetylene reduction, 14 C, assimilation, excretion of organic C as well as lower concentrations of chlorophyll a and particulate organic C compared to cultures supplied with 5, 10, and 50 mg Na + ·l −1 Sodium deficient algae released, extracellularly a higher percentage of previously fixed C as organic C. No differences in any parameter measured were demonstrable among cultures grown with 5, 10, and 50 mg Na + ·l −1 High nitrate concentrations (20 mg NO 3 − ·l −1 ) resulted in decreased rates of acetylene reduction and heterocyst numbers in. Na sufficient, and Na deficient cultures: however, decreased, cellular Na content at high NO 3 − levels occurred only in N deficient, cultures. Higher percentages of excreted organic C occurred with increasing NO 3 − concentrations in Na deficient cultures. Sodium enrichment of natural bluegreen populations with the addition of 50, 100, and 200 mg Na + ·l −1 elicited neither a stimulatory nor an inhibitory response in photosynthetic C fixation. In contrast, the addition of small amounts of Na + (5 mg·l − ) resulted in increased C fixation. However, since the Na. concentration of the lake water, at ca. 5 mg Na + ·l −1 , was sufficient for growth of the bluegreens present, sodium, is not assumed to be limiting under most natural conditions. No increase in in situ acetylene reduction rates occurred with additions of sodium.