Soluble N compounds in trees exposed to high loads of N: a comparison between the roots of Norway spruce (Picea abies) and beech (Fagus sylvatica) trees grown under field conditions

amino acids ammonia ammoniac arbre forestier azote chemical composition composition chimique cycle de l'azote exsudat exudados exudates fagus sylvatica forest trees modele modelos models mycorrhizae nitrate nitrates nitratos nitrogen nitrogen cycle picea abies pollution racine roots sap savia seasonal variation