Comparative effects of salinity and water stress on photosynthesis, water relations and growth of Jatropha curcas plants

The aim of this study was to evaluate the physiological responses of physic nut (Jatropha curcas L.) plants exposed to water stress and salinity in order to elucidate some acclimatory mechanisms. Mild water and salt stresses were imposed by plant exposure to -0.22 MPa iso-osmotic solutions with PEG 6000 or NaCl 50 mM for 8 days. Stress recovery was evaluated under control conditions after three and eight days. PEG treatment caused higher reductions in Ψw and Ψs, but both relative water content and succulence were not affected by the two stress treatments, compared to the control. The PEG-stressed plants suffered higher restrictions in leaf growth compared to the salt-stressed ones. Moreover, only the PEG treatment caused a pronounced effect on leaf membrane integrity. Both treatments caused similar impairment of the CO2 assimilation rate, but the PEG stressed plants showed higher restriction in stomatal conductance and transpiration. Although both stresses caused significant decreases on the leaf chlorophyll content, the photochemical activity was not affected. Since the plants subjected to mild water and salt stresses showed a rapid and almost complete recovery, these physiological alterations could represent a set of adaptive mechanisms employed by J. curcas to cope with these stressful conditions.