Impact of forest tree species on feldspar weathering rates

An in situ experimental approach was used to test the impact of several for est tree species on weathering of a plagioclase used as a test-mineral. Tre e species were Norway spruce, Scots pine, sessil oak, pedunculated oak and European beech. The experiment was carried out by putting a fixed mass of t est-mineral into the soil under different tree species stands located in th e same conditions. Test-minerals were inserted into soils at various depths (0, 5, 15, 30 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 u nder litters (0-cm depth). At 0- and 5-cm depth, dissolution rates signific antly decreased over the 9 years of the experiment. There was a significant positive linear relation between specific surface area of test-minerals an d their mass losses. Test-mineral evolution in mass and specific surface ar ea was strongly dependent on environmental conditions, mostly soil pH and s oil 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. C oniferous species promoted mass losses more significantly than broadleaved species did. Tree species provoked more or less mass losses through modific ations in the acidity of the soil. (C) 2000 Elsevier Science B.V. All right s reserved.