The Combined Effects of Salinity and Drought on Young Almond Trees and Physiological Parameters

In drought years, almond growers have to restrict fresh water application, either stressing the trees with inadequate water or adding saline water and reducing water stress but causing salt stress. Tree response to combined water and salt stress are critical consideration on management decisions but there is no appropriate information currently. That's why, it was investigated the water and salt stress and combined water-salt stress on two almond varieties in a two year (2015 and 2016) outdoor experiment with young trees. Trees were 1 year old at the beginning of the experiment. The experiment was conducted USDA (United States Department of Agriculture) Salinity Laboratory, Riverside, California, USA. Drought treatments consisted of 100%, 80% and 60% of tree evapotranspiration (ET) and salt treatments of Electrical Conductivity (EC= 0.55, 1.20, 2.40 and 3.0 dS m-1), for a total of 120 trees in twelve treatments with two varieties and five replicates. We examined water use, trunk diameter and physiological parameters (leaf net photosynthetic rate, stomatal conductance and leaf water potential). Photosynthetic rate values (Pn) ranged between 3.53 and 11.08 mu mol CO2 m-2 s-1 for Nonpareil and 4.58 and 9.48 mu mol CO2 m-2 s-1 for Aldridge. Stomatal conductance values ranged between 0.076 and 0.283 mol H2O m-2 s-1 for Nonpareil and 0.097 and 0.302 for Aldridge. All parameters showed significant decline starting at 80% water application and EC 1.2 dS m-1. In terms of growth rather than survival, almond was sensitive to water as well as salt stress. We evaluated combined stress using three stress response models: additive stress, dominant stress model and a multiplicative stress model where the predicted growth loss is obtained by multiplying the relative growth response for the individual stresses. Equation (2) for reduction in trunk growth were developed for treatments with either salinity only or water only stress. Both varieties grafted to Nemaguard rootstock were very sensitive to salinity with growth loss starting at EC 1.2 dS m-1. The results indicate that the Nonpareil is more sensitive to drought and salt stress than Aldridge. Aldridge almond variety can be recommended for areas where water supplies are scarce and salinized.