|Abstract or Summary
- Batch cultures of Skeletonema costatum were grown under continual
light saturation, with nitrogen nutrients in limiting concentrations.
Population parameters measured included ¹⁴C uptake,
chlorophyll a, particulate carbon and nitrogen, and ammonia, nitrate,
and nitrite, concentrations.
A method was developed for measuring cellular nutrient reservoirs
in laboratory cultures of marine phytoplankton. The method
seems compatible to field measurements of cellular reservoirs in
natural plankton communities. Significant cellular nutrient reservoirs
of nitrate and ammonia were measured in all three experiments,
and the ratio of mg/1 of cellular nutrient reservoir to mg/1 of particulate
nitrogen ranged from zero to 1.0.
Cellular nitrite reservoirs ranging from 0-1μM were observed
during nitrite assimilation, A practical method of measuring nitrate reservoirs was developed.
From the raw data, parameters calculated were nutrient
specific uptake rates, particulate nitrogen specific growth rates,
relative cellular reservoir size, percent soluble organic nitrogen,
photosynthetic assimilation ratios, chlorophyll a / carbon ratios,
and nitrogen to carbon ratios.
Specific uptake rates were found to be highly variable, and at
times were ca. 20 times the highest measured population growth
rate. It was concluded that specific uptake rates showed poor correlation
to specific growth rates. Calculated relative cellular nutrient
reservoir sizes do not correspond directly to trends in specific
growth rates, although it was noted that large relative cellular
nutrient reservoir sizes preceded the initial large increases in
particulate nitrogen specific growth rates.
Photosynthetic assimilation ratios and percent soluble organic
nitrogen correlate with trends in population growth rate very well.
Changes in N/C ratios, and chlorophyll a / carbon ratios were also
found to be related to changes in population growth rates. The N/C
values ranged from 0.04 to 0.16, and the corresponding C/N ratios
from 15 to 6. 2. Induction of the chlorophyll a synthesis pathway by
internal ammonia concentrations is discussed.
Four basic models of phytoplankton growth dynamics are discussed,
and the inadequacy of each model, in light of past and present experimental evidence is pointed out.
A new conceptual model is presented and discussed, which
appears to be biologically sound and compatible with experimental
evidence. The most important aspect of the model is the induction
of assimilatory enzyme systems by internal nutrient concentrations.