Adaptation of soil bacterial communities to prevailing pH in different soils

The bacterial community response to pH was studied for 16 soils with pH(H2O) ranging between 4 and 8 by measuring thymidine incorporation into bacteria extracted from the soil into a solution using homogenization-centrifugation. The pH of the bacterial solution was altered to six different values with dilute sulfuric acid or different buffers before measuring incorporation. The resulting pH response curve for thymidine incorporation was used to compare bacterial communities from the different soils. There was a correlation between optimum pH for thymidine incorporation and the soil pH(H2O). Even bacterial communities from acid soils had optima corresponding to the soil pH, indicating that they were adapted to these conditions. Thymidine incorporation was also compared with leucine incorporation for some soils. The leucine to thymidine incorporation ratio was constant over the tested pH interval when incorporation values were adjusted for isotope dilution. A good correlation was found between the scores along the first component (explaining 80% of the variation) and soil pH (r(2) = 0.85), if principal component analysis of the pH response curves for thymidine incorporation was used. The pH response curves differed most for the extreme pH Values used, and a linear relationship was found between the logarithm of the ratio of thymidine incorporation at pH 4.3 to incorporation at pH 8.2 and the soil pH (r(2) = 0.86). Thus, a simplified technique using only two pH values, when measuring the thymidine incorporation, could be used to compare the response to pH of bacterial communities.