The symbiosis between Rhizobium and Parasponia andersonii was examined under a range of nutrient regimes in agar tube culture. Nodule initiation and nitrogen fixation were stimulated with ‘starter’ nitrogen. Nitrogenase activity of plants in tubes was similar to plants in Leonard jars or pots and resembled, when expressed on a nodule weight basis, the activity of other non–legumes rather than legumes.
Fifteen isolates of Rhizobium from Parasponia were compared for effectiveness in nitrogen fixation in controlled environment cabinets. All rhizobia produced nodules and only one failed to fix nitrogen. The others varied in their degree of effectiveness, the least effective yielded only 70 % of the plant top weight of the best symbiotic combination. A few ineffectively nodulated plants occurred in all rhizobial treatments. Their presence was considered to be a result of host variability rather than environmental factors.