ACCLIMATION OF NITRATE UPTAKE BY PHYTOPLANKTON TO HIGH SUBSTRATE LEVELS¹

Abstract

A literature review of data on nitrate uptake by phytoplankton suggests that nitrate levels above 20 lmol N . L À 1 generally stimulated uptake rates in cultured unicellular algae and natural phytoplankton communities. This phenomenon indicates that phytoplankton cells acclimate to elevated nitrate levels by increasing their uptake capacity in a range of concentrations previously considered to be saturating. Cyanobacteria and flagellates were found to present a considerable capacity for acclimation, with low (0.1-2 lmol N . L À 1 ) half-saturation values (K s ) at low (5-20 lmol N . L À 1 ) substrate levels and high (1-80 lmol N . L À 1 ) K s values at high (30-100 lmol N . L À 1 ) substrate levels. However, some diatom genera (Rhizosolenia, Skeletonema, Thalassiosira) also appeared to possess a low affinity nitrate uptake system (K s between 18 and 120 lmol N . L À 1 ), which can help resolve the paradox of their presence in enriched seas. It follows that present models of nitrate uptake can severely underestimate the effects of high nitrate concentrations on phytoplankton dynamics and development. A more adequate approach would be to consider the possibility of multiphasic uptake involving several phase transitions as nitrate concentrations increased. Because it is a nonlinear phenomenon featuring strong thresholds, this effect appears to override that of other variables, such as irradiance, temperature, and cell size. Within the present context of eutrophication and for a range of concentrations that is becoming more and more ecologically relevant, equations are tentatively presented as a first approach to estimate K s from ambient nitrate concentrations.

PISCES-v2: an ocean biogeochemical model for carbon and ecosystem studies

“…The three parameters in this equation (P max , K P ,min i , and S P rat ) can be independently specified for each phytoplankton group. Finally, observations also suggest that these half-saturation constants should vary with the mean nutrient concentrations, probably as an acclimation to the local environment (Collos et al, 1980;Smith et al, 2009). This acclimation mechanism is not included in PISCES, except for the case of silicate (see Sect.…”

The effect of inorganic nitrogen speciation on primary production in the San Francisco Estuary

“…In this study we observed classical MichaeliseMenten kinetics for NH 4 but were unable to determine N uptake kinetics for NO 3 , although comparing rates obtained with saturating level of the two DIN species, there was higher V MAx for NO 3 compared to NH 4 . Deviation (to linear or biphasic) from the hyperbolic relationship for NO 3 uptake at saturating to supersaturating concentrations have been described in many algal species including diatoms (Serra et al, 1978;Watt et al, 1992;Collos et al, 1992Collos et al, , 1997Collos et al, , 2005Lomas and Glibert, 1999b) and upwelled phytoplankton . Two studies (Huntsman and Barber, 1977;Lancelot and Billen, 1985) showed that C and N uptake were coupled during linear NO 3 uptake at high concentrations.…”

Modeling the seasonal autochthonous sources of dissolved organic carbon and nitrogen in the upper Chesapeake Bay

“…The half saturation constants for the uptake of ammonium and nitrate by phytoplankton were used to tune (optimize) the model. Thus they were set at values, which fall within the ranges reported for the uptake of ammonium and nitrate by phytoplankton at high nutrient concentrations (Collos et al, 2005;Eppley et al, 1969), reflecting the high nitrate and ammonium concentrations found at station CB3.3C throughout much of the year. The half saturation constants were also set so that the uptake affinity for ammonium of small phytoplankton is stronger than that of large phytoplankton (Stolte et al, 1994).…”