In Turkey, one of the major crops threatened by salinity due to sea water intrusion is citrus since they are grown mainly in the coastal areas benefiting from the suitable climatic conditions. In the western Aegean region, two rootstocks, Poncirus trifoliata and Troyer citrange are used for Satsuma mandarins. An experiment was designed to search the effects of five different salinity levels ranging between 0.65 and 6.5 dS m(-1); additional impact of potassium (0-100-200 g K2O/tree) through fertigation was studied. The results proved that the leaf stomatal density was affected by the rootstocks. The reduction parallel to salinity was stable in Poncirus whereas Troyer responded by a sharp decline especially at higher salinity levels. Photosynthetic rate and thus water use efficiency (photosynthesis/transpiration) were decreased significantly as the salinity of the irrigation water increased.