Effects of growing roots of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) on rhizosphere soil solution chemistry

The chemical conditions of the rhizosphere can be very different from that of bulk soil. Up to now, little attention has been given to the problem of spatial heterogeneity and temporal dynamics of rhizosphere soil solution and little is known about the influence of different tree species on rhizosphere chemistry. In the present study, we used micro suction cups to collect soil solution from the rhizosphere of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) seedlings in high spatial resolution and capillary electrophoresis for the determination of major cations and anions. The results indicate, that in a soil with a base saturation of about 20-25% and a pH of 6.5, growing roots of beech and spruce lower the concentrations of nutrient cations and nitrate in the rhizosphere soil solution and decrease significantly the pH. The H+ release leads to an enhanced mineral weathering as indicated by an increase of CEC and base saturation and to a mobilization of soluble Al, however, on a very low concentration level. In our experiment rhizosphere effects of spruce have been more pronounced than those of beech, indicating, that with respect to below ground activity young spruce trees have a better competitive power than beech.