Physiological implications of legume nodules associated with soil acidity

Abstract

The mutualistic legume–rhizobia symbiosis that leads to nodule formation and ensuing nitrogen fixation is of great importance to soil health and agriculture sustainability. The processes of nodulation and nitrogen fixation can improve the nitrogenous content and overall structure of the rhizosphere; however, they are highly sensitive to environmental parameters, such as soil acidity. Indeed, low pH conditions can appreciably diminish the benefits associated with legumes and can decrease their biomass and yields. This is of considerable economic and agricultural importance as legume crop and pasture species are commonly grown on acidic soils. Acidic growing conditions can reduce the overall fitness of both the legume host and the rhizobia partner, in addition to directly hindering the establishment of nodule structures. This includes impairing the signal exchange between the two symbiotic partners and inhibiting their ability to express critical nodulation genes. The effect of soil acidity on legume and rhizobia growth is addressed here, with a focus on nodule development and function. Practices to help overcome limitations associated with growing legumes in low pH environments are addressed, with an emphasis on how current biotechnology and molecular genetic approaches could aid in overcoming the negative effects associated with low pH