Effect of low root temperature on symbiotic nitrogen fixation and competitive nodulation of Onobrychis viciifolia (sainfoin) by strains of arctic and temperate rhizobia

Summary

Symbiotic effectiveness and competitive nodulation of the temperate forage legume sainfoin (Onobrychis viciifolia cv. Melrose) by two strains of arctic rhizobia (from Astragalus or Oxytropis sp.) and two strains of temperate rhizobia (from sainfoin) were evaluated at temperatures of 9, 12, or 15°C for roots and 20°C (day) and 15°C (night) for shoots. The inocula consisted of effective individual or paired arctic and temperate strains which were identified on the basis of differential growth. At 9°C, the arctic strains were generally more competitive than the temperate strains, whereas at the highest temperature tested, the converse was apparent. Symbiotic effectiveness (shoot dry weight, nitrogenase activity, and number of nodules) was similarly affected by root temperature, except that at 15°C the arctic strains were generally as effective as the temperate strains. The marked interaction between temperature and strain on competitiveness or on effectiveness indicates symbiotic adaptation of the arctic rhizobia to low temperatures. On the basis of these data we suggest that the use of selected, cold-adapted rhizobia in sainfoin inoculants may be beneficial in temperate regions where low soil temperatures occur early in the growing season.