Eliciting the aboveground physiological regulation that underlies salinity tolerance in faba bean (Vicia faba L.)

Salinity is a prevalent soil issue that reduces crop growth by a combination of osmotic stress and ion-specific toxicity. The crop response to salt stress is generally described in terms of a two phase model in which growth is initially reduced by osmotic stress and then Na⁺ toxicity. However, the relative importance of these mechanisms to salt stress is still not well understood. In this study a high-resolution image capture and analysis system was used to monitor shoot growth of faba bean plants non-destructively, while gas exchange measurements were used to examine the effects on photosynthesis in order to gain an understanding of the aforementioned stress mechanisms. The results of this soil-based study suggested that responses of crop growth to salinity stress depend on its severity: osmotic stress was the predominant cause of reduced growth at high levels of salinity, while specific-ion toxicity was more important under mild stress. We showed that the tolerant faba bean variety used dual mechanisms of ion exclusion and osmotic tolerance compared with the sensitive variety. Analysis of photosynthetic responses indicated that the extent to which stomatal closure affects photosynthetic capacity is indicated by the magnitude of the reduction in intercellular CO₂ concentration.