Effect of calco-magnesian amendment on the mineral weathering abilities of bacterial communities in acidic and silicate-rich soils

Liming of forest ecosystem is recognized to increase nutrients availability in soil and water and to enhance the biomass and bacterial activities in soil. However, little studies have investigated on change induced on bacterial ability to alter silicate mineral after soil liming. Thus, this study is carried out in experimental conditions using podzol collected in the winter (2007), spring and summer (2008) in small forest catchments in Vosges Mountains amended in 2003 by dolostone and limestone. Bacterial communities, extracted from various horizons of these soils amended or not, were put in contact with a phyllosilicate (phlogopite as sole source of Mg and Fe) in miniaturized bioassays in aerobic conditions. A weathering phenotype was determined through the quantification of (i) protons and organic acids released in assay solution by bacteria (ii) iron leached from phlogopite lattice into solution by bacteria and (iii) the carbon source consumption (i.e. glucose). These results were then compared to empirical model based on chemical leaching experiments realized in the same conditions in order to simulate the processes involved. In parallel, the carbon source utilization patterns of bacteria were investigated in order to discriminate the bacterial communities from amended and non-amended soil horizons. The results indicate that (1) the total bacterial biomass was unaffected by the Ca–Mg amendment, whereas the cultivable bacterial biomass increased after the amendment, and (2) the weathering and the carbon source utilization patterns of bacterial communities differs from one soil horizon to another and among soil types. The metabolic profiles analyzed indicated significant differences in organic C substrate usage depending on season and Ca–Mg amendment. Bacterial communities, extracted from the amended soil, are enable greater iron leaching compared to those found in the control soil, suggesting a greater release of organic acids and/or a more highly chelating organic acid release. The process developed by bacteria to alter the phillosilicate is complexolysis. We conclude that the Ca–Mg amendment had a positive effect on the functional richness of bacterial communities extracted from soil and on their potential to weather minerals that was present after several years.