Tree bark and soil ammonia oxidizers: a molecular study on a historical forest of Central Italy

The composition and activity of ammonia-oxidizing bacteria (AOB) in soil and tree-bark of a pine forest of Central Italy were investigated by molecular methods because it is known that soil pH is an important environmental factor structuring the soil macrofauna community in the tree vicinity, but, the effects of the stemflow on the composition of soil microbial communities have been poorly studied. The 16S rDNA fingerprintings showed that the AOB population of the bark was similar to that of soil (pH 3.66) receiving the acid stemflow of pine, whereas the composition of the AOB population of the less acid soil (pH 4.90) sampled 150 cm from the trunk was different. Ammonia-oxidizing activity increased significantly moving from the trunk outwards, parallel with a progressive increase in soil pH.