Sime, Iain; (1997) An eco-physiological investigation of nutrient limited growth and competition between five species of planktonic diatoms. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This study investigated phosphorus and silicon competition between five species of planktonic diatoms and the results were interpreted with specific reference to information from published field studies. Asterionella formosa, Tabellaria flocculosa var. asterionelloides, Cyclostephanos dubius, Cyclotella radiosa and Cyclotella aff. gordonensis, which have different field-derived phosphorus optima, were grown in artificial media. Growth characteristics under phosphorus and silicon limitation were defined from batch culture experiments using the Monod model. There were few statistically significant differences between the species' kinetic parameters under phosphorus limitation, but clearer differences were found in their relative abilities to compete for silicon. Each species' phosphorus and silicon minimum cell quotas were measured. When ranked by increasing minimum cell quotas, the species order differed slightly from their competitive ability rankings for each resource. This discrepancy produced some unstable equilibrium points when predictions were made about the outcome of competition along dual resource gradients. Competition experiments were designed to test predictions made from the results of the batch culture experiments and to investigate the predicted unstable equilibrium points. The competition experiments confirmed the predictions based on the growth kinetic parameters. The experiments also confirmed that some of the species' competitive interactions were unstable, a new finding for diatom ecology. The competition experiments were unable to clarify the outcome of competition between the three predicted best competitors for phosphorus. This suggests that the Monod model may be insufficiently refined to differentiate the relative competitive abilities of oligo- to mesotrophic species under phosphorus limitation. The predicted competitive abilities were compared to phosphorus optima produced from a lake training set. The ordering of the species by each method showed general agreement, indicating that phosphorus is indeed a crucial nutrient in the ecology of freshwater diatoms. The relative abilities of the species to compete for silicon also agreed with published field studies.

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