DISTRIBUTION OF BIOMASS AND NITROGEN AMONG PLANT-PARTS AND SOIL-NITROGEN IN A YOUNG ALNUS-INCANA STAND

Grey alder, Alnus incana (L.) Moench, was inoculated with the local source of Frankia and planted in nitrogen-poor soil in northern (63.8-degrees-N, 20.3-degrees-E) Sweden. Each alder root system was enclosed in a cylinder that served as an open-ended cuvette for nitrogenase activity measurements. The alders grew well, especially during the 2nd year of the study. The final leaf area in each season was more closely related to total alder biomass than final height of alders. The alders lost 17% of their total dry mass as leaf litter each year. This corresponded to 33 g dry mass and 0.67 g N per alder during the 2nd year. During the 2 years the soil N increment was 0.52 g N per alder. Leaf litter N and the increase in soil N corresponded to 27 and 17%, respectively, of the N2 fixed in the 2 years. Already at a young age, N2-fixing A. incana can apparently contribute to an improved fertility of N deficient soils.