DEVELOPMENT AND LONG-TERM SALT TOLERANCE OF PISTACHIOS FROM PLANTING TO MATURITY USING SALINE GROUNDWATER

Impact of Drought and Changing Water Sources on Water Use and Soil Salinity of Almond and Pistachio Orchards: 1. Observations

Soil salinity increases when growers are forced to use higher salinity irrigation waters due to water shortages. It is necessary to estimate the impact of irrigation water on soil properties and conditions for crop growth to manage the effects of salinity on perennial crops. Therefore, in this study, we monitored root zone salinity in five almond and pistachio orchards in eastern and western San Joaquin Valley (SJV), California (CA). Volumetric soil water contents and bulk electrical conductivities were measured at four root-zone depths. Evapotranspiration was measured by eddy covariance along with three other types of data. The first is seasonal precipitation and irrigation patterns, including the temporal distribution of rains, irrigation events, and irrigation water salinity. The second is soil chemistry, including the initial sodium adsorption ratio (SAR) and soil solute electrical conductivity (ECe). The third type is the physical properties, including soil type, hydraulic conductivity, and bulk density. As expected, we found low salinity at the eastern sites and higher salinity at the western sites. The western sites have finer textured soils and lower quality irrigation water; measured actual ET was about 90% of modeled crop ET. Across the three western sites, the annual average apparent leaching fraction ranged from 11 to 28%. At the eastern sites, measured ET almost exactly matched modeled crop ET each year. Apparent leaching fractions in the eastern sites were approximately 20%.

Sodium interception by xylem parenchyma and chloride recirculation in phloem may augment exclusion in the salt tolerant Pistacia genus: context for salinity studies on tree crops

Working in tandem with root exclusion, stems may provide salt-tolerant woody perennials with some additional capacity to restrict sodium (Na) and chloride (Cl) accumulation in leaves. The Pistacia genus, falling at the nexus of salt tolerance and human intervention, provided an ideal set of organisms for studying the influences of both variable root exclusion and potentially variable discontinuities at the bud union on stem processes. In three experiments covering a wide range of salt concentrations (0 to 150 mM NaCl) and tree ages (1, 2 and 10 years) as well as nine rootstock-scion combinations we show that proportional exclusion of both Na and Cl reached up to ~85% efficacy, but efficacy varied by both rootstock and budding treatment. Effective Na exclusion was augmented by significant retrieval of Na from the xylem sap, as evidenced by declines in the Na concentrations of both sap and wood tissue along the transpiration stream. However, while we observed little to no differences between the concentrations of the two ions in leaves, analogous declines in sap concentrations of Cl were not observed. We conclude that some parallel but separate mechanism must be acting on Cl to provide leaf protection from toxicity specific to this ion and suggest that this mechanism is recirculation of Cl in the phloem. The presented findings underline the importance of holistic assessments of salt tolerance in woody perennials. In particular, greater emphasis might be placed on the dynamics of salt sequestration in the significant storage volumes offered by the stems of woody perennials and on the potential for phloem discontinuity introduced with a bud/graft union.