Quantifying root and shoot trait responses of jojoba (Simmondsia chinensis) to irrigation-induced salinity

The responses of young, bearing jojoba ( Simmondsia chinensis ) grown in inert media to irrigation water with salinity ranging from 1.74 to 15.46 dS m⁻¹ were studied over two years. Increasing salinity reduced photosynthesis, stomatal conductance, vegetative branching, and biomass, indicating clear physiological and growth limitations. In contrast, reproductive traits showed a threshold-dependent response, with fruit set and seed yield reaching their maximum near 12 dS m⁻¹ before declining at higher salinity. This indicates a possible stress-escape strategy where young to reproductive phase transition is accelerated as a salinity response mechanism. Mineral analysis of plant material showed strong tissue-specific partitioning, with roots accumulating the highest Na⁺ and Cl⁻ concentrations, while young leaves maintained relatively low Na⁺ levels compared with mature leaves. This suggests that jojoba utilizes a spatiotemporal ion partitioning strategy where roots sequester toxic ions while mature leaves function as temporary salt sinks, contributing to salt removal through leaf turnover. Despite overall reductions in K as a function of increased salinity, the canopy maintained a significantly higher K + /Na + ratio than the roots, which is crucial for sustained physiological function. Minirhizotron observations indicated continued root expansion and turnover across salinity treatments, with no evidence of root-system collapse or root-related salinity response mechanisms. The findings suggest that brackish-water irrigation may be feasible for jojoba and may support early reproductive performance.