Formation of cluster roots in Alnus incana ssp rugosa and other Alnus species

Small numbers of cluster roots were found on older roots of Alnus incana ssp, rugosa (speckled alder) shrubs in thf field at 2 of 11 sites. Cluster roots also formed infrequently in speckled alder grown hydroponically in complete nutrient solution. No fluster roots formed in solutions lacking P or Fe. Small numbers of cluster roots also formed in Alnus glutinosa grown hydroponically in the presence of P but not in its absence, In contrast, Alnus rubra produced small numbers of cluster roots in the absence of P but not in its presence. No cluster roots formed in Alnus viridis ssp. crispa. Cluster roots are probably not important Dr nutrient uptake in speckled alder because they form infrequently both in the field and in hydroponic culture.