Effects of N:P ratios on the uptake of nitrate and phosphate by laboratory cultures ofTrichodesmium erythraeum (Ehr.)

Abstract

The paper reports observations on the uptake of phosphate and nitrate by the Blue Green alga,Trichodesmium erythraeum, in axenic cultures with varying N:P ratios. The ratio of the increase of the phosphate absorption (Δp) to increase in phosphate concentration (ΔP) and also the ratio of increase of nitrate absorption (Δn) to increase in nitrate concentration (ΔN) were determined. Increase of concentration of phosphate in the medium increased the rate of absorption of phosphate but had no effect of nitrate absorption. Increase of concentration of nitrate had a positive influence on both nitrate and phosphate absorption. In media with N:P ratios ranging from 20:1 to 20:5 the Δp/ΔP was 2·1. With N:P concentration of 20:10 in the medium the Δp/ΔP was 0·9, and in media with N:P ratio 20:15 it was 0·1. With regard to effect of nitrate in media with N:P ratios ranging from 1:1 to 15:1, the Δn/ΔN was 0·29 and Δp/ΔP was 0·06; in media of 20:1 to 25:1 Δn/ΔN was 0·67 and Δp/ΔP was 0·1. The coefficient of cell increase (K) did not show any appreciable change with increase of concentration of either N or P in the medium.