Phosphorus utilization byAsterionella formosaHass

Abstract

Observations have been made on the relationship in Lake Windermere between the growth of Asterionella formosa and the concentration of dissolved phosphate. Asterionellaformosa has also been grown in culture and the amount of phosphorus required by this organism has been determined. These experiments have shown that: (1) Asterionella can take up and store in reserve phosphorus from concentrations below those found in phosphorus-poor lakes (i.e. below 1 μg.P/l.). (2) Growth can continue in phosphorus-deficient media by making use of such reserves, cell phosphorus being steadily reduced. (3) The limiting requirement per cell of phosphorus is very minute—about 0—06μg P/10 ⁶ cells/1, so that initial concentrations as low as rog.P/l. can theoretically produce a population of some i6 x io6 cells/l. before limitation by phosphorus deficiency. This has been realized in culture. The behaviour of Asterionella formosa growing in nature has been found to conform with that found in culture. It is concluded from such observations that phosphorus deficiency is unlikely to provide a limit to growth of Asterionella in Windermere, despite the very low initial concentration of dissolved phosphate. Further experiments have shown that Asterionella cells low in phosphorus can rapidly take up added phosphate from lake water but not from distilled water. Some factors which affect the rate of phosphate uptake of depleted cells are investigated, and attempts have ben made to throw some light on the nature of the apparent difference between lake water on the one hand and distilled water and a number of artificial lake waters on the other. No conclusion is reached on the reason why Asterionella cells behave differently in lake water and in artificial media.