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

Thymidine, leucine and acetate incorporation into soil bacterial commu nities extracted from two different soils using homogenisation-centrif ugation were measured at different temperatures (0-28 degrees C). Simi lar effects of temperature were found for both soils used. Optimum tem peratures 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 f it to the square root model (Ratkowsky model) was found for all three methods, when only data below optimum was considered for the acetate i ncorporation. The apparent T-min calculated from this model was -8.4+/ -0.77 degrees C for thymidine incorporation. T-min for acetate incorpo ration was slightly higher. Leucine incorporation had significantly hi gher T-min (- 6.0+/-0.62 degrees C), and the Q(10) between 0 and 10 de grees C was also higher than for the two other measurements. This resu lted in a leucine/thymidine incorporation ratio which increased from 0 degrees C up to about 15 degrees C, but remained constant at temperat ures above 15 degrees C. The amount of leucine incorporated into hot a cid insoluble material (protein) as a percentage of that incorporated into cold acid insoluble material (total macromolecules) was also cons tant above 15 degrees C (about 40%), but decreased at lower temperatur es to less than 25%. No effects were found of temperature on non-speci fic 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 soi l 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.