| Popis: |
This work examined the sinking rate (ψ) patterns in Cricosphaera carterae Braarud cultures as they underwent progressive nutrient impoverishment with respect to specific substrates (e.g., NO−3, NH+4, PO−4). The buoyancy patterns following cessation of nutrient inputs showed dependence upon the pre-conditioning nutrient experience and, under NO−3 -limitation, the specific growth rate of the original population. PO−4 -limited populations showed progressive ψ increases with increasing culture age. NO−3 and NH+4-limited populations displayed short-term increases in ψ, followed by decreasing ψ with progressive senescence. These findings suggest that nutrient history resulted in physiological differences which were evidenced in the senescence-related buoyancy response. Under NO−3-limitation, the relationship between growth rate and ψ appeared to be due to variable growth potentials, based upon intracellular reserves. The persistence of diurnal buoyancy variation in the face of declining metabolic activity implies that the responsible physiological mechanism is related to a basal metabolic function. The short-term buoyancy response to a perturbation of the steady-state uptake system shows an instantaneous elevation of the population ψ. These results are consistent with the hypothesis that buoyancy regulation is related to an energy-requiring process. |
