Ecophysiological studies onEuphorbia paraliasunder soil salinity and sea water spray treatments

Euphorbia paraliasL. was studied on the coastal dunes in Egypt, and its seeds were germinated under greenhouse conditions and subjected to 0, 200 and 400 m soil salinity in combination with one or two sprays per day by sea water. Phytosociological studies revealed greater importance value forE. paraliasat slightly saline locations and on the sea side of the coastal sand dunes. The plant also exhibited low transpiration rate and relative water content but high dry matter content in the dry (summer and autumn) compared with the wet seasons (winter and spring). Under greenhouse conditions,E. paraliasresponded to the imposed stresses by: decreasing daily mean transpiration, shifting the time of maximum transpiration to be at the time of minimum evaporative demand of the atmosphere, attaining several peaks of transpiration corresponding to favourable conditions, and exhibiting noticeable night transpiration. Combined stress of high soil salinity and sea water spray greatly inhibited plant control of water loss. Salinity alone or in combination with once a day sea water spray decreased transpiration. CO2fixation at night, as indicated by the accumulation of malic acid, indicated transformation of plant photosynthesis into a CAM pathway. Salinity alone greatly increased night malic acid accumulation compared to sea water spray. The percentage of dead leaves increased after treatments, but the high control on water loss and increased dry matter by night fixation of CO2increased plant water-use efficiency.