Gas Exchange and Mineral Nutrition of 12 Viburnum Taxa Irrigated with Saline Water

More than half of residential water in Utah is used for landscape irrigation. Reclaimed water has been used to irrigate urban landscapes to conserve municipal water. High salt levels in reclaimed water may pose osmotic stress and ion toxicity to salt-sensitive plants. Viburnums are commonly used landscape plants, but salinity tolerance of species and cultivars is unclear. The objective of this study was to characterize gas exchanges and mineral nutrition responses of 12 viburnum taxa subjected to salinity stress in a greenhouse study. Plants were irrigated with a nutrient solution at an electrical conductivity (EC) of 1.3 dS·m–1 or saline solution at an EC of 5.0 dS·m–1 or 10.0 dS·m–1. The net photosynthesis rate (Pn), stomatal conductance (gS), and transpiration rate (E) of all viburnum taxa, except for Viburnum ×burkwoodii and V. בNCVX1’, decreased to various degrees with increasing salinity levels. The Pn, gS, and E of V. ×burkwoodii and V. בNCVX1’ were unaffected by saline solutions of 5.0 dS·m–1 at the 4th and 9th week after treatment initiation, with the exception of the Pn of V. ×burkwoodii, which decreased at the 9th week. Leaf sodium (Na+) and chloride (Cl–) concentrations of all viburnum taxa increased as salinity levels increased. Viburnum ×burkwoodii had relatively low leaf Na+ and Cl– when irrigated with saline solutions of 10.0 dS·m–1. Plant growth and gas exchange parameters, including visual score, plant height, Pn, gS, E, and water use efficiency (WUE) correlated negatively with leaf Na+ and Cl– concentrations. The ratio of potassium (K+) to Na+ (K+/Na+) and ratio of calcium (Ca2+) to Na+ (Ca2+/Na+) decreased when salinity levels increased. Visual score, plant height, Pn, gS, E, and WUE correlated positively with the K+/Na+ and Ca2+/Na+ ratios. These results suggest excessive Na+ and Cl– accumulation inhibited plant photosynthesis and growth, and affected K+ and Ca2+ uptake negatively.