Changes in soil bacterial communities following liming of acidified forests

To counteract forest decline due to anthropogenic acidification, two catchments located on granite and on sandstone bedrock were limed (2.5 t/ha). The catchments are located in strongly affected areas in the Vosges Mountains of northeastern France. Four years after liming, structure of soil bacterial communities and community-level physiological profiling (CLPP) were investigated at two seasons. Bacterial communities were compared with those of two reference adjacent catchments to highlight changes induced by liming. Denaturing gradient gel electrophoresis (DGGE) and Biolog Ecoplate (TM) analysis revealed that liming modified the structure of bacterial communities and the CLPPs, suggesting that moderate large-scale liming has a sustainable impact on bacterial communities of forest soils. Moreover, significantly higher responses from limed soils were observed for a larger number of Biolog Ecoplate substrates compared to control soils. Analysis of 16S rRNA gene clone libraries showed that taxonomic diversity was slightly lower in limed soils, particularly within acidobacterial and Gram-positive groups, whereas proteobacterial diversity increased in limed soils. The relative abundance of dominant taxa showed that the ratio between Proteobacteria and Acidobacteria was higher in limed soils. This large-scale field study documents the effects of a four year old liming on bacterial communities of forest soils by providing a common indicator based on analysis of metabolic potential activities of heterotroph communities and by identifying major taxonomic changes in bacterial community structure. The results confirm previous observations showing that the ratio between Proteobacteria and Acidobacteria could be a microbial indicator of soil quality improvement. (C) 2011 Elsevier B.V. All rights reserved.