Water status and osmotic adjustment of broad-bean (Vicia faba L.) in response to soil salinity

Broad-bean (Vicia faba L.) crops were grown in lysimeters filled with two types of soil with different (loam and clay) and they were irrigated with waters of three different levels of salinity (corresponding to 3.7, 15 and 30 meq l(-1) of Cl-). During the crop season the soil salinity was determined in each lysimeter by means of the salt balance. Measuring regularly the pre-dawn leaf-water potential and the stomatal conductance, the water stress of broad-bean was monitored during the whole crop cycle. Osmotic adjustment was determined by analysing the pressure-volume soil water curves at four growth stages. The two water stress parameters showed good coherence, since they indicated systematic differences between saline treatments and the control irrigated with fresh water. Soil texture did not affect the water stress parameters. Broad-bean demonstrated a clear inability to do any effective osmotic adjustment, and as a consequence the effect of the osmotic adjustment on stomatal opening is negligible. However, the broad-bean plants maintained high their stomatal conductance under every salinity level. These results allow to examine different hypotheses which could explain the origin of broad-bean sensitivity to salinity.