Impact of dolomite lime on the ground vegetation and on potential net N transformations in Norway spruce (Picea abies (L.) Karst.) and sessile oak (Quercus petraea (Matt.) Lieb.) stands in the Belgian Ardenne

The impact of dolomite lime (5 T.ha(-1)) on the ground vegetation and on po tential net nitrogen (N) transformations was investigated in two Belgian fo rest ecosystems. Norway spruce (Picea abies (L.) Karst.) and sessile oak (Q uercus petraea (Matt.) Lieb.) stands were situated in the Haute Ardenne (ea st Belgium) on acid-brown soil. The herb-layer floristic richness increased during the 2 years following liming, with the appearance of light and N-de manding species, which are also found in clear-cut areas or on road verges. Mosses reacted rapidly, showing a decrease acidophilous-dominant species a nd the establishment of some ruderal species. Six months after liming, the pH was significantly increased in the organic horizon of both stands and in the organomineral horizon of the oak stand. Soils originating from the two stands showed distinct responses in net NO3- production to the dolomite li me treatment. In the organic layer of the Quercus soil, net NH4+ production was decreased, NO3- prediction increased, and total N mineralisation remai ned unchanged. In the organomineral layer. NO3- production was increased. I n the Picea soil, NO3- production was decreased in the organomineral soil l ayer. These results indicate the possibility of differences in the control of the N transformation processes occurring in the two sites. ((C) Inra/Els evier, Paris.).