Hydrogen Uptake (Hydrogenase) Activity of Rhizobium Japonicum Strains Forming Nodules in Soybean Production Areas of the U.S.A.

Abstract

Root nodules of soybeans (Glycine max) inoculated with most strains of Rhizobium japonicum release considerable amounts of hydrogen whereas nodules from a minority of strains evolve little if any H2 (Lim, 1978; Schubert and Evans, 1977; Evans et al., this volume, and the extensive reference list of this paper). A number of studies have pointed toward a significant benefit of the H2 uptake system to overall plant productivity (see above references) since energy limitation is one of the major factors in nitrogen fixation in soybeans (Hardy and Havelka, 1975). A comparison of soybean productivity in experiments conducted with Hup+ (strains with an active H2 uptake system) and Hup” (strains which lack an active H2 uptake system) strains of Rhizobium japonicum have shown that the Hup+ strains are more efficient symbionts (see Evans et al., this volume). In addition, a comparison of plants (grown in the greenhouse and growth chamber) inoculated with isogenic Hup− mutants (derived from Hup+ parents) fixed significantly less nitrogen and had reduced yields than the parent Hup+ strain which synthesized the hydrogenase system (Albrecht et al., 1979; and discussion by Evans et al., this volume, on the isogenic nature of these strains). Thus, the capacity to synthesize an active H2 uptake system may be a desirable characteristic of Rhizobium spp.