Resource competition among saline-lake diatoms under varying N/P ratio, salinity and anion composition

1. A series of resource competition experiments were performed with four diatom taxa isolated from saline lakes in the Northern Great Plains of North America. Three variables were tested in a factorial design: N/P ratio (6 : 1, 12 : 1, 24 : 1, 48 : 1), salinity (5, 8, 11 00), and anion composition (sulphate versus bicarbonate-dominated medium). 2. Coexistence of Chaetoceros elmorei, Cyclotella quillensis, and Cymbella pusilla occurred at the two lowest N/P ratios. These three taxa have similar N requirements and thus competitive exclusion by the taxon with the lowest N requirement may have required more time. 3. Anomoeoneis costala, which had the highest nitrogen requirements and slowest growth rate of these four taxa, declined in all cases. Cyclotella biovolume concentration consistently declined at the two highest N/P ratios, indicating a higher P requirement, which is consistent with its distribution pattern. 4. In general, we found opposite trends with respect to all variables for Chaetoceros, a taxon that mainly inhabits sulphate systems, versus Cymbella, a bicarbonate-associated taxon. Our results suggest that Cymbella may be found mainly in bicarbonate systems because of a higher C requirement, whereas Chaetoceros may be less abundant in these systems, in part, because of competitive interactions with bicarbonate-associated taxa.