Chasing the Mechanisms of Ecologically Adaptive Salinity Tolerance

Plants adapted to challenging environments offer fascinating models of evolutionary change. Importantly, they also give important information to meet our pressing need to develop resilient, low-input crops. With mounting environmental fluctuation - including temperature, rainfall, soil salinity and degradation - this is more urgent than ever. Happily, solutions are hiding in plain sight: the adaptive mechanisms from natural adapted populations, once understood, can then be leveraged. Much recent insight has come from the study of salinity, a widespread factor limiting productivity, with estimates of 20% of all cultivated lands affected. This is an expanding problem, given increasing climate volatility, rising sea levels and increasing irrigation. We therefore highlight recent benchmark studies of ecologically adaptive salt tolerance in plants, assessing macro- and microevolutionary mechanisms, and the recently recognised role of ploidy and the microbiome on salinity adaptation. We synthesise insight specifically on naturally evolved adaptive salt-tolerance mechanisms, as these works move substantially beyond traditional mutant or knockout studies, to show how evolution can nimbly 'tweak' plant physiology to optimise function. We then point to future directions to advance this field, that intersects evolutionary biology, abiotic-stress tolerance, breeding and molecular plant physiology.