The effect of inoculation with either cultured Frankia or crushed nodules on nodulation and growth of Alnus rubra and Alnus glutinosa seedlings in forest nurseries

Abstract The growth of seedlings of Alnus rubra and Alnus glutinosa is chemically sterilised seed beds in forest nurseries in Scotland and southern England was enhanced considerably after inoculation with Frankia in comparison with uninoculated seedlings receiving PK and, in most experiments, NPK fertiliser. Alnus rubra seedlings inoculated with an elite Frankia strain, UGL Ar 1.2.5q, isolated from nodules from a Scottish plantation of A. rubra and characterised previously in climate chamber experiments, showed greater growth than seedlings inoculated either with crushed. A. rubra nodules from the same plantation or with Ar I4, a North American Frankia strain. After inoculation with Ar 1.2.5q, seedlings showed faster growth, were more robust and had a higher N content than plants from seed beds receiving standard nursery fertilisers (basal NPK or basal NPK + NK top-dressing). Inoculation of A. glutinosa see beds with Frankia UGL Ag 1.1.8 also stimulated greater growth of seedlings than fertiliser treatments. With this species, pre-germination application of inoculum promoted seedling growth more than application post-germination. For both species, foliar nutrient analysis showed that concentrations of phosphorus and calcium were influenced strongly by seedling inoculation and were inversely correlated with growth and foliar nitrogen concentrations. The results emphasise the importance of inoculation for the production of robust, rapidly growing seedlings in nurseries and illustrate the advantages of inoculation with selected strains of Frankia .