Plant Growth Promoting Rhizobacteria and Soybean Glycine max(L.) Merr. Nodulation and Nitrogen Fixation at Suboptimal Root Zone Temperatures

Co-inoculation of plant growth promoting rhizobacteria (PGPR) with Bradyrhizobium has been shown to increase legume nodulation and nitrogen fixation at optimal soil temperatures. Nine rhizobacteria co-inoculated with Bradyrhizobium japonicum 532C were tested for their ability to reduce the negative effects of low root zone temperature (RZT) on soybean Glycine max (L.) Merr. nodulation and nitrogen fixation. Three RZTs were tested: 25 (optimal), 17.5 (somewhat inhibitory), and 15°C (very inhibitory). At each temperature some PGPR strains increased the number of nodules formed and the amount of fixed nitrogen when co-inoculated with B. japonicum, but the stimulatory strains varied with temperatures. The strains that were most stimulatory varied among temperatures and were as follows: 15°C, Serratia proteamaculans 1-102; 17.5° C, S. proteamaculans 1-102 and Aeromonas hydrophila P73; 25°C, Serratia liquefaciens 2-68.