Experimental calibration of Ellenbergʹs indicator value for nitrogen

Ellenbergʹs indicator values constitute a relative scale of optima per species with regard to several soil factors, mainly based on field experience. For the coupling of soil and vegetation models these optima have to be expressed in metric units. The aim of this study was to explore the utility of germination experiments to calibrate the indicator values for nutrients against nitrogen availability. Germination and juvenile development were followed 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 concentration was estimated on the basis of percentages germination, survival, formation of cotyledons and formation of leaves. The estimated optima were regressed on the indicator values for nutrients (Ellenbergʹs N). A significant correlation was found for percentage germination and formation of leaves. The observed relation can be used to calibrate the Ellenberg scale for N.