Glasshouse evaluation of the growth of Alnus rubra and Alnus glutinosa on peat and acid brown earth soils when inoculated with four sources of Frankia

Abstract

The effects of soil type (an acid peat and 2 acid brown earths) and Frankia source (3 spore-positive crushed nodule inocula and spore-negative crushed nodules containing the single Frankia ArI5) on nodulation, N content and growth of Alnus glutinosa and A. rubra were determined in a glasshouse pot experiment of two years duration. Plants on all soils required additional P for growth. Growth of both species was very poor on peat with A. glutinosa superior to A. rubra. The former species was also superior to A. rubra on an acid brown earth with low pH and low P content. Some plant-inoculum combinations were of notable effectivity on particular soils but soil type was the major source of variation in plant weight. Inoculation with crushed nodules containing Frankia ArI5 only gave poor infection of the host plant, suggesting that inoculation with locally-collected crushed nodules can be a preferred alternative to inoculation with Frankia isolates of untested effectivity. Evidence of adaptation of Frankia to particular soils was obtained. Thus, while the growth of all strains was stimulated by mineral soil extracts, inhibitory effects of peat extracts were more apparent with isolates from nodules from mineral soils than from peat, suggesting that survival of Frankia on peat may be improved by strain selection.