Use of radiolabelled thymidine and leucine to estimate bacterial production in soils from continental Antarctica

Tritiated thymidine incorporation (TTI) into DNA was used to examine bacterial production in two soil types from the Robertskollen group of nunataks in northwestern Dronning Maud Land, providing the first estimates of bacterial production in soil habitats on the Antarctic continent. Although estimates of bacterial productivity in soils near to bird nests (344 +/- 422 ng of C g [dry weight](-1) h(-1)) were higher than those for soils from beneath mosses (175 +/- 90 ng of C g [dry weight](-1) h(-1); measured by TTI at 10 degrees C), these differences were not significant because of patchiness of bacterial activity (P > 0.05). TTI- and [C-14]leucine ([C-14]Leu)-derived estimates of bacterial production were similar when incubations of 3 h were used, although incubations as short as 1 h were sufficient for measurable uptake of radiolabel. Dual-label incorporation of [H-3]thymidine ([H-3]TdR) into DNA and [C-14]Leu into protein indicated that TTI did not reflect bacterial production of in situ assemblages when incubations were longer than 3 h. Isotope dilution analysis indicated that dilution of the specific activity of exogenously supplied [H-3]TdR by de novo synthesis of TdR precursor could be limited by additions of [H-3]TdR at a concentration of 1 nmol per ca. 115 mg of soil. TTI exhibited a psychrotrophic response to variation in temperature, with a temperature optimum of ca. 15 degrees C and a Q(10) value for 0 to 10 degrees C of 2.41.