THYMIDINE, LEUCINE AND ACETATE INCORPORATION INTO SOIL BACTERIAL ASSEMBLAGES AT DIFFERENT TEMPERATURES

Thymidine, leucine and acetate incorporation into soil bacterial communities extracted from two different soils using homogenisation-centrifugation were measured at different temperatures (0-28 degrees C). Similar effects of temperature were found for both soils used. Optimum temperatures for incorporation of acetate into lipids were found between 20 and 24 degrees C, while the incorporation of thymidine and leucine into cold acid insoluble material increased with temperature. A good fit to the square root model (Ratkowsky model) was found for all three methods, when only data below optimum was considered for the acetate incorporation. The apparent T-min calculated from this model was -8.4+/-0.77 degrees C for thymidine incorporation. T-min for acetate incorporation was slightly higher. Leucine incorporation had significantly higher T-min (- 6.0+/-0.62 degrees C), and the Q(10) between 0 and 10 degrees C was also higher than for the two other measurements. This resulted in a leucine/thymidine incorporation ratio which increased from 0 degrees C up to about 15 degrees C, but remained constant at temperatures above 15 degrees C. The amount of leucine incorporated into hot acid insoluble material (protein) as a percentage of that incorporated into cold acid insoluble material (total macromolecules) was also constant above 15 degrees C (about 40%), but decreased at lower temperatures to less than 25%. No effects were found of temperature on non-specific incorporation of thymidine into macromolecules other than DNA, or acetate incorporation into different lipid fractions (neutral, glyco- and polar lipids). The fact that the temperature relationships for soil bacterial communities appeared to follow the square root model will facilitate comparisons of such relationships between different soils, as well as recalculation of data to actual field temperatures.