Experimental calibration of Ellenberg's indicator value for nitrogen

Ellenberg's indicator values constitute a relative scale of optima per spec ies with regard to several soil factors, mainly based on field experience. For the coupling of soil and vegetation models these optima have to be expr essed in metric units. The aim of this study was to explore the utility of germination experiments to calibrate the indicator values for nutrients aga inst nitrogen availability. Germination and juvenile development were follo wed during a maximum of six weeks on five NH4NO3 levels and two pH levels. Per plant species (19 in total) the optima with regard to NH4NO3 concentrat ion was estimated on the basis of percentages germination, survival, format ion of cotyledons and formation of leaves. The estimated optima were regres sed on the indicator values for nutrients (Ellenberg's N). A significant co rrelation was found for percentage germination and formation of leaves. The observed relation can be used to calibrate the Ellenberg scale for N.