Increasing Root Zone Ca+2 Concentration Will Decrease Uptake and Transport of Na+ and Enhance Plant Growth of Pistacia Species Grown in Saline Soils

As surface water supplies dwindle and become more saline in California, the pistachio industry faces the challenge of managing orchards on increasingly saline soils with less water. Currently, the only approach we have for managing and alleviating the effects of root zone salinity is leaching. Methods of managing soil salinity that do not require more water would have great horticultural value. Recent research with the pistachio species, P. lentiscus, demonstrated that increasing the root zone Ca⁺² levels mitigated the effects of root zone salinity by reducing Na⁺ uptake to the leaves during salinity stress. Additional research on P. lentiscus and olive, reported when osmatic stress was relieved by leaching with quality water (relief period), both photosynthesis and growth rate recovered faster when previously treated with high Ca⁺² compare to low Ca⁺² treatment. These studies motivated us to investigate the specific effects of increasing root zone Ca⁺² on Na⁺ uptake, transport and plant growth in ‘Kerman’ trees (California’s most common pistachio scion) budded on PGI, UCBI clonal, and UCBI seedling rootstocks grown in saline soils. Based on recent reports, we hypothesized increasing that the Ca⁺² concentration in saline root zones may decrease the uptake of Na⁺ to ‘Kerman’ scions grown on different pistachio rootstocks. Additionally, during the relief period photosynthetic performance and therefore growth rate would recover faster. Our objectives for this project are (Ι) to rank the differences in tree water status, gas exchange, and ion distribution among ‘Kerman’ scions’ grown on different rootstocks under saline conditions (ΙΙ), to determine how Ca⁺² treatments affect these parameters; and (ΙΙΙ), to determine if trees respond better to leaching if pretreated with Ca⁺². Every two weeks, photosynthesis and gas exchange characteristics, stomatal conductance (gs) and CO₂ net assimilation rate (Asat) will be measured using a Li-Cor 6400 under 100% solar irradiance measured by Li-i800 spectroradiometer. Tree water status will be measured on leaves sampled at predawn using a pressure bomb. Leaf osmotic potential (ψπ) will be measured on expressed sap of these frozen and thawed leaves with a freezing-point Osmomat 030 osmometer (Gonotec, Berlin, Germany) equipped with a 15-μL measuring cell. Leaf turgor potential (Ψp) will be calculated as the difference between (Ψw) and (Ψπ).  Ion distribution will be analyzed on leaves for Ca⁺², Na⁺, and K⁺ at two-week intervals by samples sent to the University of California analytical lab.