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Similar NH[SUB4,SUP+] and NO[SUB3,SUP-] uptake kinetic patterns were observed in Neoagardhiella baileyi (Harvey ex Kützing) Wynne & Taylor and Gracilaria foliifera (Forsskål) Borgesen. NO[SUB3,SUP-] was taken up in a rate-saturating fashion described by the Michaelis-Menten equation. NH[SUB4,SUP+] uptake was multicomponent: a saturable component was accompanied by a diffusive or a high K component showing no evidence of saturation (at ⩽50 μM [NH[SUB4,SUP+]). Nitrogen starved plants (CIN atom ratios >ca. 10) showed higher transient rates of NH[SUB4,SUP+] uptake at a given concentration than plants not N-limited. Only plants with high N content transient rates of NH[SUB4m,SUP+] uptake rates, and showed transient rates of NH[SUB4,SUP+] accumulation which did not greastly exceed the capacity to incorporate N in steady-state growth. NH[SUB4,SUP+] was preferred over NO[SUB3,SUP-], even in plants preconditioned on NO[SUB3,SUP-] as the sole N source. NO[SUB3,SUP-] uptake was suppressed at 5 μM [NH[SUB4,SUP+]. But simulataneous uptake occurred at unsurpressed rates at lower concentrations. Potential for N accumultion was greater via NH[SUB4,SUP+] uptake than via NO[SUB3,SUP-] uptake. Changing capacity for NH[SUB4,SUP+] uptake with N content appears to be a mechanism whereby excessive accumulation of N was abvoided by N-satiated plants but large accumulation was possible for N-depleted plants. [ABSTRACT FROM AUTHOR]

Gracilaria foliifera (Forsskål) Borgesen and Neoagardhiella baileyi (Harvey ex Kützing) Wynne & Taylor were grown in continuous-flow culture under cocentration of nitrogen enrichment supplied to the plants. Growth rate appeared to follow saturation-type nutrient uptake kinetics for plants receiving ammonium, nitrate, urea or sewage effluent enrichments. Ammonium enrichment produced higher growth rates than nitrate or sewage enrichment. The lowest growth rates occurred in the chambers receiving unenriched seawater or urea. Half saturation constants (K) for growth were in the range of 0.2-0.4 μM N for all N enrichments examined. The low estimated values of K compare closely with those found for microalgae and indicate that both species possess the ability to utilize very low concentrations of N. [ABSTRACT FROM AUTHOR]