Changes in the growth rates of saline-lake diatoms in response to variation in salinity, brine type and nitrogen form

The growth rates of four saline-lake diatom taxa were measured under varying conditions of salinity (5, 8 and 11 parts per thousand), brine type (sulfate- versus bicarbonate-dominated) and nitrogen form (NH4+ versus NO3-), using a full factorial design. With NO3- as the nitrogen source, Cyclotella quillensis, Cymbella pusilla and Anomoeoneis costata exhibited lower growth rates in the sulfate versus bicarbonate media. The strain of Chaetoceros elmorei used in these experiments, isolated from a sulfate-dominated lake, was unable to grow on NO3- alone. In the NH4+ treatments, neither salinity nor brine type affected the growth rates of C. quillensis or C. elmovei. When supplied with NH4+, C. pusilla and A. costata had higher growth rates in the bicarbonate versus sulfate media, although for C. pusilla the difference on NH4+ was not as great as on NO3-. The impact of brine type on NO3- use is consistent with the theory that sulfate inhibits molybdate uptake, as molybdenum is required for NO3- use but not NH4+. Cymbella pusilla was the only taxon affected by changes in salinity. The four taxa used in these experiments are frequently found in saline lakes and saline-lake sediments, hence they are used in paleoclimate reconstructions; the results presented here provide additional information that may enhance these diatom-based reconstructions.