Impact of forest tree species on feldspar weathering rates

An in situ experimental approach was used to test the impact of several forest tree species on weathering of a plagioclase used as a test-mineral. Tree species were Norway spruce, Scots pine, sessil oak, pedunculated oak and European beech. The experiment was carried out by putting a fixed mass of test-mineral into the soil under different tree species stands located in the same conditions. Test-minerals were inserted into soils at various depths (0, 5, 15, 40 cm) and then maintained over two periods (3 and 9 years). At the end of their incubation period, test-minerals were collected, weighed and analysed. Mass losses of test-minerals were highest for bags inserted under litters (0-cm depth). At 0- and 5-cm depth, dissolution rates significantly decreased over the 9 years of the experiment. There was a significant positive linear relation between specific surface area of test-minerals and their mass losses. Test-mineral evolution in mass and specific surface area was strongly dependent on environmental conditions, mostly soil pH and soil type. Test-minerals which were inserted into soil layers of low acidity (pH >4.5) had very low mass losses and specific surface area increments. Coniferous species promoted mass losses more significantly than broadleaved species did. Tree species provoked more or less mass losses through modifications in the acidity of the soil.