Occurrence of Alnus-infective Frankia and Trifolium-infective Rhizobium incircumpolar soils

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 te sted for the occurrence of Rhizobium infective on Trifolium pratense. Infec tivity tests were performed by growing test seedlings in soil or soil suspe nsions. Frankia was detected only in very few soils, in spite of extended e xperimental periods. When nodulation took place, nodulation was observed in few test plants. Several of nodulated test seedlings never turned green, s uggesting that Frankia was ineffective in N-2 fixation. An exception was so il from a site in the Faeroe Islands where nodulated Alnus had been introdu ced. This soil showed high nodulation ability and N-2 fixation was likely. It is suggested that lack of infective Frankia in the circumpolar soils stu died may be because Frankia had not been spread to these sites, but does no t necessarily mean that soil conditions are negative for Frankia. Infective Rhizobium was rare in the soils studied. Lack of infective root nodule bac teria in potential sites for soil reclamation calls for the need to inocula te the plants and also provides the opportunity for introduction of selecte d bacterial strains without competition from an endogeneous soil microflora .