Survival of rhizobia in Saskatchewan soils as influenced by freeze/thaw cycling

Abstract

Rhizobium leguminosarum biovar viceae are not native to Saskatchewan, but numbers of rhizobia in excess of l0^4 g-1 soil have been observed in fields previously grown to inoculated field pea (Pisum sativum L.). Modified immunoblot and ELISA techniques utilizing strain-specific polyclonal antibodies were used to monitor the survival of rhizobial populations under freeze/thaw conditions in field and controlled environment studies. Total rhizobial populations tended to decrease with each freeze/thaw cycle, but there were not always significant differences between pre- and post-freeze rhizobial populations. Total rhizobial numbers tended to be affected more by a fallow period then by the freeze/thaw cycle itself. The effect of soil moisture content at freezing on total populations varied with strain. The proportion of the total rhizobial population able to nodulate field pea was not affected by the freeze/thaw cycle, but a decrease during the fallow period was observed.