Effects of Nitrate and Phosphate Limitation on Cyclostat Growth of Two Freshwater Diatoms

Abstract

~~ ~The effects of N and P limitation on cell division and on cellular contents of limiting and non-limiting nutrients were examined in cyclostat cultures of the freshwater diatoms Asterionella formosa and Fragilaria crotonensis. Nutrient-limited cell cycles of both species were readily entrained by a 14 h/10 h light/dark cycle. In I;: crotonensis, the maxima relative to the onset of the light phase of the photocycle occurred at approximately -1 to + 1 h for cell division, + 1 1 to 13 h for cell N, and +21 to 23 h for cell P. In A . formosa the maxima occurred at approximately + 3 to 10 h for cell division and +2 to 4 h for cell N and cell P. Changes in culture dilution rate (integrated growth) and in the type of nutrient limiting growth did not significantly alter these times for either species. The cell-number oscillations can be explained by a simple exponential function for the instantaneous population growth rate, which occurs after a single modal transition time z, which is characteristic for each species.The consistency of phase relations between N and P limitations and culture dilution rates suggests that the temporal organization for events within the cell cycle of each organism is independent of the nutrient-limited status of the cell populations.

DIEL RHYTHM OF ALGAL PHOSPHATE UPTAKE RATES IN P‐LIMITED CYCLOSTATS AND SIMULATION OF ITS EFFECT ON GROWTH AND COMPETITION1

“…Before counting, the cell suspensions of C. vulgaris and A. convolutus were sonicated for 30 s at a setting of 2 and 50% duty cycle, using a sonicator (Vibra Cell, Sonics & Materials Inc., Danbury, CT, USA) equipped with a tapered tip probe. As a result, any aggregated cell clusters were dispersed into single cells, thereby avoiding a decrease in the cell count (Gotham and Rhee 1982).…”

“…Sommer (1994) showed that different day lengths and light intensities bring about the dominance of different species. Hence, diel rhythms in the nutrient uptake rate relative to the L:D cycle have been thought to cause temporal variations in the limiting nutrient (Gotham and Rhee 1982, Shin et al 1987), thereby enhancing the possibility of coexistence even if the competing species have identical optimum ratios (Rhee and Gotham 1980). An analysis of the theoretical model suggests that a variation in the consumption rate could allow two or more competitors to coexist even though limited by the same resource (Abrams 1984).…”

Advances in Microbial Ecology

“…Only the period average growth is related to the lowest cell quota during the cycle (Rhee et al. 1981;Gotham and Rhee, 1982). Like the Monod equation, therefore, cell quota models are valid only for nonperiodic environments or for the comparable time in the division cycle.…”