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

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The growth rates of four saline-lake diatom taxa were measured under varying conditions of salinity (5, 8 and 11‰), brine type (sulfate- versus bicarbonate-dominated) and nitrogen form (NH4 + versus NO3 - ), using a full factorial design. With NO3 - as the nitrogen source, Cyclotella quil- lensis, 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.elmorei. 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 infor- mation that may enhance these diatom-based reconstructions.