Patterns of nodulation and nitrogen fixation of actinorhizal plants with different sources of Frankia microsymbionts have been only partially elucidated. In one series of experiments, species of rosaceous Dryas, Cowania, Cercocarpus, Fallugia and Purshia were inoculated with Frankia isolates, crushed Dryas nodules and neoglacial soils to ascertain nodulation patterns. Neoglacial soils from Alaskan and Canadian sites where Dryas drumondii occurred naturally nodulated not only Dryas drumondii but also Cercocarpus betuloides, Cowania mexicana and Purshia tridentata , all rosaceous actinorhizal plants from distant southerly locales. Crushed nodules from D. drumondii nodulated D. drumondii , as well as C. betuloides, C. mexicana and P. tridentata and non-rosaceous Elaeagnus, Myrica and Shepherdia spp. Nodules produced by C. mexicana and P. tridentata reduced acetylene to ethylene, indicating nitrogenase activity.

No actinorhizal nodules were produced by any of eight isolates of Frankia , including two from P. tridentata and one from C. mexicana . These latter results indicate the presence of Frankia strains other than those able to nodulate the specific host in rhizospheres of nodules, and as contaminants purported to be nodular isolates of the rosaceous hosts.

Direct evidence for facilitation of associated plant growth by provision of N during primary succession by N2 -fixing plant species is lacking in most studies of neoglacial communities. In a second study the δ 15 N method was used to determine that D. drumondii did not fix N until about 70 years post-glaciation within the forelands of the montane Athabasca Glacier in Canada. The timing of evidence for N 2 -fixation in this study coincided with δ15 N values from about 70 years post-glaciation suggestive of transfer of fixed N to associated plants. There remains uncertainty concerning N processes in chronosequence studies of glacial deposits in general. When, or if, transfer of fixed N between the N2 -fixing and non-N2 -fixing plant species starts remains largely unknown in most such primary successional studies.

In a separate study, water-retentive polymer carriers of Frankia inoculum were applied as a root dip to Alnus glutinosa and Casuarina equisetifoloia seedlings. This treatment increased nodulation 5- to 10-fold in greenhouse experiments and also of A. glutinosa in a field experiment.