ADAPTATION OF SOIL BACTERIAL COMMUNITIES TO PREVAILING PH IN DIFFERENT SOILS

The bacterial community response to pH was studied for 16 soils with p H(H2O) ranging between 4 and 8 by measuring thymidine incorporation in to bacteria extracted from the soil into a solution using homogenizati on-centrifugation. The pH of the bacterial solution was altered to six different values with dilute sulfuric acid or different buffers befor e measuring incorporation. The resulting pH response curve for thymidi ne incorporation was used to compare bacterial communities from the di fferent soils. There was a correlation between optimum pH for thymidin e incorporation and the soil pH(H2O). Even bacterial communities from acid soils had optima corresponding to the soil pH, indicating that th ey were adapted to these conditions. Thymidine incorporation was also compared with leucine incorporation for some soils. The leucine to thy midine incorporation ratio was constant over the tested pH interval wh en incorporation values were adjusted for isotope dilution. A good cor relation was found between the scores along the first component (expla ining 80% of the variation) and soil pH (r(2) = 0.85), if principal co mponent analysis of the pH response curves for thymidine incorporation was used. The pH response curves differed most for the extreme pH Val ues 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.