EFFECT OF TREE SPECIES AND SOIL PROPERTIES ON NUTRIENT IMMOBILIZATIONIN THE FOREST FLOOR

To investigate the effect of tree species and soil properties on organ ic matter accumulation and associated nutrients, an area-based samplin g of the forest floor was carried out in a 28 years old species trial including Norway spruce, Douglas fir, beech, and common oak at two sit es, a poor and sandy soil, and a fertile loamy soil. The accumulation of C, N and P in the forest floor was significantly higher at the sand y site than at the loamy site under all species. At the loamy site, oa k was characterized by lesser accumulation of C, N and P than the othe r species. Remarkably, the C/N-ratios showed no substantial difference s, whereas the C/P-ratios were significantly higher at the sandy site for all species. pH was significantly lower at the sandy site for all species, and among the species, pH was lower in the conifer forest flo ors than in the broadleave forest floors. The concentration of ammoniu m, nitrate and phosphate in the soil solution was much higher at the l oamy site under all species showing a stronger microbial activity. It is therefore hypothesized that the differences in accumulation rates w ere, at least partly, caused by differences in the mineralization regi mes. Strong root infiltration in the forest floors at the sandy site c ompared to almost none at the loamy site, is probably responsible for the differences in mineralization rate due to competition between the organic matter decomposers and the tree-roots/mycorrhiza for nutrients .