Occurrence of Alnus-infective Frankia and Trifolium-infective Rhizobium in Circumpolar Soils

Abstract

A survey was made of the occurrence of Frankia, infective on Alnus, in some 40 soils from the whole circumpolar area. Some of these soils were also tested for the occurrence of Rhizobium infective on Trifolium pratense. Infectivity tests were performed by growing test seedlings in soil or soil suspensions. Frankia was detected only in very few soils, in spite of extended experimental periods. When nodulation took place, nodulation was observed in few test plants. Several of nodulated test seedlings never turned green, suggesting that Frankia was ineffective in N2 fixation. An exception was soil from a site in the Faeroe Islands where nodulated Alnus had been introduced. This soil showed high nodulation ability and N2 fixation was likely. It is suggested that lack of infective Frankia in the circumpolar soils studied may be because Frankia had not been spread to these sites, but does not necessarily mean that soil conditions are negative for Frankia. Infective Rhizobium was rare in the soils studied. Lack of infective root nodule bacteria in potential sites for soil reclamation calls for the need to inoculate the plants and also provides the opportunity for introduction of selected bacterial strains without competition from an endogeneous soil microflora.