The rate of change of a soil bacterial community after liming as a function of temperature

The response of a bacterial community to liming of a forest humus soil (pH 4.9 increased to pH 7.5) was studied in the laboratory at three temperatures (5, 20, and 30°C). As a comparison an unlimed soil (pH 4.9) and a soil limed in the field 15 years ago (pH around 6) were also included. The bacterial community tolerance of pH was measured using TdR incorporation. The pH of the bacterial suspensions (bacteria directly extracted from soil) was altered to 3.6 and 8.3 using different buffers before measuring TdR incorporation. The logarithmic ratio between TdR incorporation at 8.3 and 3.6 was then used as an indicator of the community pH tolerance. The rate of changes in the community tolerance to pH after liming was fastest for the soil incubated at 30°C, but only minor differences in rate of change could be seen between samples incubated at 5 and 20°C. Changes in phospholipid fatty acid (PLFA) pattern after increasing the pH were most rapid for the bacterial community in the soil incubated at 30°C followed by the soil incubated at 20°C, whereas no changes could be seen in the PLFA pattern of the soil incubated at 5°C, even after 82 days’ incubation. Thus, the changes in the PLFA pattern were considerably slower than the changes in bacterial community tolerance to pH measured using TdR incorporation.