Paudel, I., Institute of Soil, Water and Environmental Sciences, ARO Volcani Center, Bet Dagan, Israel, The Robert H. Smith Faculty of Food Agriculture and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
Shaviv, A., Technion-Israel Institute of Technology, Haifa, Israel
Bernstein, N., Institute of Soil, Water and Environmental Sciences, ARO Volcani Center, Bet Dagan, Israel
Heuer, B., Institute of Soil, Water and Environmental Sciences, ARO Volcani Center, Bet Dagan, Israel
Shapira, O., The Robert H. Smith Faculty of Food Agriculture and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
Lukyanov, V., Institute of Soil, Water and Environmental Sciences, ARO Volcani Center, Bet Dagan, Israel
Bar-Tal, A., Institute of Soil, Water and Environmental Sciences, ARO Volcani Center, Bet Dagan, Israel
Rotbart, N., Institute of Soil, Water and Environmental Sciences, ARO Volcani Center, Bet Dagan, Israel
Ephrath, J., Jacob Blaustein Institutes for Desert Research, The Ben Gurion University of the Negev, Sde Boqer, Israel
Cohen, S., Institute of Soil, Water and Environmental Sciences, ARO Volcani Center, Bet Dagan, Israel

Water quality, soil and climate can interact to limit photosynthesis and to increase photooxidative damage in sensitive plants. This research compared diffusive and non-diffusive limitations to photosynthesis as well as photorespiration of leaves of grapefruit trees in heavy clay and sandy soils having a previous history of treated wastewater (TWW) irrigation for >10years, with different water qualities [fresh water (FW) vs TWW and sodium amended treated wastewater (TWW+Na)] in two arid climates (summer vs winter) and in orchard and lysimeter experiments. TWW irrigation increased salts (Na+ and Cl-), membrane leakage, proline and soluble sugar content, and decreased osmotic potentials in leaves of all experiments. Reduced leaf growth and higher stomatal and non-stomatal (i.e. mesophyll) limitations were found in summer and on clay soil for TWW and TWW+Na treatments in comparison to winter, sandy soil and FW irrigation, respectively. Stomatal closure, lower chlorophyll content and altered Rubisco activity are probable causes of higher limitations. On the other hand, non-photochemical quenching, an alternative energy dissipation pathway, was only influenced by water quality, independent of soil type and season. Furthermore, light and CO2 response curves were investigated for other possible causes of higher non-stomatal limitation. A higher proportion of non-cyclic electrons were directed to the O2 dependent pathway, and a higher proportion of electrons were diverted to photorespiration in summer than in winter. In conclusion, both diffusive and non-diffusive limitations contribute to the lower photosynthetic performance of leaves following TWW irrigation, and the response depends on soil type and environmental factors. © 2016 Scandinavian Plant Physiology Society.