Growth and water relations of three geographically separate origins of maritime pine (Pinus pinaster) under saline conditions.

Water relations and growth of maritime pine (Pinus pinaster Ait.) were investigated in 2-year-old seedlings of French ('Landes'), Iberian ('Iberian') and Moroccan ('Tamjoute') origin raised for 67 days in a flowing solution culture system containing 0, 50, 150 or 250 mM NaCl. Height growth, and stem, needle and root dry matter were reduced by salinity with minor differences among geographic origins. Predawn needle water potential was decreased by salinity and corresponded approximately to the osmotic potential of the nutrient solution. Stomatal conductance was reduced according to the amount of salinity applied. Whole-plant hydraulic conductance was also reduced, even when expressed on a root dry weight basis. The osmotic potential of xylem sap was five- to sixfold lower than that of the nutrient solution. Seedlings of the most southerly origin (Tamjoute) exhibited a greater ability to decrease osmotic potential under saline conditions than seedlings of more northerly origin (Landes and Iberian) as a result of higher mineral cation transport to the shoot.