Gas exchange, water relations and osmotic adjustment in two scion/rootstock combinations of Prunus under various salinity concentrations

Growth, gas exchange and water relations have been studied on hydroponically grown peach (cv. Armking) plants, grafted on GF(677) (Arm/GF) and Mr. S.(2/5) (Arm/MrS), exposed to 0, 40, 80 and 120 mM NaCl concentration, over a four-week period. Plant performance was also evaluated during a subsequent four-week period of relief from stress, by supplying the plants with a complete nutrient solution. Salinity stress reduced growth and net assimilation rate to a greater extent in Arm/GF than in Arm/MrS plants. Salt-induced water stress was more severe in Arm/GF than Arm/MrS leaves, and particularly during the first two weeks of treatment. On the other hand, leaf osmotic potential at full turgor (Psi(piFT)) of salt-treated Arm/MrS received a markedly greater contribution from Na+ and Cl- than salt-treated Arm/GF plants. By contrast, divalent cations and K+ made a substantially greater contribution to leaf Psi(piFT) of salt-treated Arm/GF than to the corresponding Psi(piFT) of Arm/MrS plants. Salinity stress markedly altered leaf carbohydrate composition and led to a preferential accumulation of sorbitol, independent on the scion/rootstock combination. Salt-treated Arm/GF but not Arm/MrS plants stored most of the Na+ and Cl- loaded in the shoot, into basal (old) leaves. The rootstock ability to control the accumulation of salt in the scion leaves during the salinity stress, determined striking differences in the recovery of photosynthetic performances, during the relief period. A full recovery of A and g(s) was detected in both 40 and 80 mM salt-treated Arm/GF leaves, but only in 40 mM salt-treated Arm/MrS, at the end of the relief treatment. These data indicate a greater efficiency of GF(677) than Mr.S.(2/5) in protecting peach plants from the deleterious effects of NaCl stress.