Rhizobia at Extremes of Acidity, Alkalinity, Salinity, and Temperature

Symbiosis and nitrogen fixation are an utmost requirement in agricultural system and global nitrogen (N) cycling. However, the soil’s harsh conditions such as acidity, alkalinity, salinity, and temperature are the primary challenges to plant-microbe interaction. Because conditions altered rapidly in soil and thus associated bacteria is failed in selection and associate with compatible host. Among the soil microbiota, rhizobia are a well-known group of bacteria for their ability to fix atmospheric nitrogen via the mechanism of symbioses with leguminous plants. These are opportunistic endosymbionts as well as saprophytic bacteria. Though soil abiotic factors have altered the activity of rhizobial populations negatively, research have proven that soil pH, salinity, and temperature are the major abiotic factors in determining the rhizobial population and their symbiotic performance. Hence, the following chapter described the integrative view of adaptation mechanism and physiological responses of rhizobia in acid, alkalinity, salinity, and temperature stress.