Although relationships among plant, biological N2 fixation, and response to soil and environmental conditions have received considerable coverage in the scientific literature, a comprehensive summary and interpretation of these interactions with specific emphasis are lacking. Fluctuations in pH, nutrient availability, temperature, and water status, among other factors, greatly influence the growth, survival and metabolic activity of nitrogen fixation bacteria. The subsequent inhibition of nitrogenase would result in O2 accumulation in the infected zones, inducing the decrease in nodule permeability. Poor nodulation of legumes in arid soils is likely due to decreases in population levels of rhizobia during the dry season. Fixation, therefore, also tends to decrease with legume age, mainly because of the concomitant increase in soil N. Calcium deficiency, with or without the confounding influence of low pH also affects attachment of rhizobia to root hairs. Rhizobia may have different tolerances to soil acidity factors than the host plant. Relatively, high-root temperature has also been shown to influence infection N2- fixation ability, and legume growth. Also, root nodulation by the bacteria can be dependent on the formation of mycorrhiza.
