Relationship between leaf gas-exchange characteristics and the performance of Ziziphus spina-christi (L.) Willd. seedlings subjected to salt stress

Ziziphus spina-christi (L.) Willd., known as Christ's thorn jujube, is a multipurpose species of the Rhamnaceae family. Seedlings were subjected to various NaCl concentrations (0 to 200 mM) for 21 d. They grew well under control conditions, however, biomass production and relative growth rate decreased with increasing NaCl salinity. This decline in growth was closely associated with a reduction in photosynthetic characteristics and plant water relations. However, the intrinsic water-use efficiency significantly increased as salt stress intensified. The relative water content declined although it still maintained high values (≥ 57%). At high salinity, plants displayed more negative stem water potential (ψw) and osmotic potential values of -2.0 and -4.0 MPa, respectively. The net photosynthetic rate and stomatal conductance were positively correlated and the former variable also had a strong positive relationship with ψw. These findings suggest that this fruit tree is quite tolerant to NaCl-salinity during its seedling stage.