Effect of NaCl on growth, photosynthesis, ion and water relations of four poplar genotypes

Cuttings of our poplar clones, Populus deltoidex x P. nigra (Dode) Guinier ev. 1-214 (P. 1-214), P. deltoides x P. nigra (Dode) Guinier f. robusta (P. Robusta), P. herolinensis and P. simonii x (P. pyramidalis x Salix matusdana) cv. Popularis 35-44 (P. Popularis) were treated with three salt levels (0, 0.5 or 1.0% w/v NaCl in sand culture for 21 days). Growth, photosynthesis, stomatal resistance, leaf water potential, and Na⁺ and K⁺ concentrations were all significantly affected by salinity. For all clones, leaf and height growth were significantly reduced after 3 and 5 days following exposure to salinity respectively. Physiological parameters (photosynthesis, stomatal resistance and pre-dawn leaf water potential) also showed rapid responses to salinity, but clonal differences were not significant. Growth, biomass partitioning and Na⁺ and K⁺ concentrations were also significantly affected by salinity. Reductions in leaf area growth were maintained throughout the duration of the experiment. Height and diameter growth were less sensitive but still showed significant differences between 0. and 0.5 and 1.0% NaCl. Proportionately less above ground biomass was produced compared with below ground (root) biomass. P. 1-214 was more vigorous than other clones and had significantly lower leaf and root Na⁺ concentrations than P. Popularis. Young leaf tissue had higher Na⁺ and K⁺ concentrations and Na:K ratios than older leaf or root tissue.