Effect of nitrate on the germination of a soil seed bank in a Norway spruce forest in relation to liming and clear-felling

Abstract: Three different kinds of humus were tested in order to examine the effect of nitrate on the germination of the seed bank of a Norway spruce experimental forest at Farabol in the south-west of Sweden: 15 years old stand without soil treatment, 15 years old stand with lime treatment (in total 6000 kg/ha limestone distributed over 12 years), and 40 years old stand without soil treatment. Using a split-plot design, three solutions were applied to the soil (0.01 M KCl, 0.01 M KNO3, and 0.0001 M KNO3) during five days. Thus, nitrate concentration in the humus samples reached values that are considered as very high and moderately high in forest soils, respectively. The samples were placed in greenhouse conditions. Seedling emergence was counted, and species were identified. Germination was contrasted with cover values of preceeding research conducted at the same experimental site. Nitrate applications had no stimulating effect on the germination of the seed bank in the greenhouse experiment, and for Calluna vulgaris germination decreased with high nitrate concentrations. Previous lime application increased the number of germinated species and the number of seedlings. It was also concluded that the effect of lime was maintained for a long time after the application, and that others unknown factors than nitrate in limed soil may stimulate germination, or that liming had increased the seed viability of a large number of species.