Growth of Oscillatoria agardhii in chemostat culture 3. Simultaneous limitation of nitrogen and phosphorus

Abstract

Simultaneous limitation of the growth rate of Oscillatoria agardhii by nitrogen (N) and phosphorus (P) was studied in chemostat cultures. Four series with different influent N/P ratios were run, and within each series the dilution rates were varied in 12 subassays. Emphasis is placed on comparing different growth models as well as estimation of growth constants in order to elucidate a possible interaction between N and P and the growth rate of the alga.

The results show that Oscillatoria was able to adapt to the different influent N/P ratios at lower growth rates, but at higher growth rates the alga seemed to use N and P in a more fixed ratio of about 12 (by weight). Growth rates as functions of the internal content of the limiting nutrient as well as the non-limiting nutrient could be described with hyperbolic equations of Fuhs' or Droop's type. N-limitation led to increased P content (q _P), and P-limitation led to increased N content (q _N).

The absolute q ₀ values are estimated to be 3% N and 0·1% P of dry weight (DW). Analyses of covariance on the q/µ data indicate some sort of interaction between simultaneous limiting N and P. The data show that the transition from N- to P-limitation was not abrupt and varied with growth rate.