Plant Tolerance to Alkaline Salinity: A Gordian Knot to Untie

Current climate change models point to soil salinization as a quickly increasing stress factor limiting crop productivity worldwide, especially under arid and semi-arid conditions. The development of salt-tolerant, high-yielding varieties of major crop species is thus an urgent breeding target. During the last decades, important advances have been made in our knowledge of the molecular mechanisms underlying tolerance to high NaCl concentrations in both model and crop species. Multiple mechanisms of Na+ compartmentation by different membrane transporters, maintenance of cell K+ levels, accumulation of osmoprotectants, and activation of antioxidant machinery have been characterized at the physiological and genetic-molecular levels. Nonetheless, the impact of this progress on the actual improvement of crop yields under saline conditions has been rather limited. Two major reasons for this failure are the multi-trait characteristic of plants’ salinity tolerance and the complexity of stress factors, besides high Na+ concentrations, curtailing the yield of crops when sown on alkaline-saline soils. Under alkaline-saline conditions plants require not only efficient Na+ tolerance mechanisms but also the ability to manage the high soil pH, the high carbonate/bicarbonate concentrations, and the low availability of essential micronutrients like Fe and Zn. This chapter addresses recent advances in the understanding of the complex physiological, molecular, and genetic mechanisms responsible for plant tolerance to alkaline salinity, envisages strategies for how to integrate this expertise into breeding programs, and highlights further research requirements to achieve this goal. Breeding efforts will be successful only when accompanied by sustainable management technologies. Recent advances in this field are also briefly addressed.