A survey of angiosperms in Nova Scotia for rhizosphere nitrogenase (acetylene-reduction) activity
Excised root samples from 901 plants, representing 130 species of nonnodulated angiosperms largely in upland, pioneering habitats, were assayed for nitrogenase activity by the acetylene-reduction technique after overnight preincubation of the samples under low pO2. Most samples and most species exhibited very low excised root acetylene-reducing activities, but for 19 species, maximum values were greater than 50 nmol C2H4∙g−1∙h−1. In situ C2H2 assays, conducted on 10 species which had exhibited maximum excised root activities greater than 10 nmol C2H4∙g−1∙h−1, indicated average belowground N2-fixation rates of 3 to 92 g N∙ha−1∙day−1 and maxima greater than 100 g N∙ha−1∙day−1 for 3 of the 10 species. The highest values were for grasses characteristic of poorly drained soils and for some dicotyledonous weeds. It is concluded that the potential of temperate-zone angiosperms for nitrogenase activity by 'associative symbioses' approaches that of tropical forage grasses.