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 (g S), and transpiration rate (E) of all viburnum taxa, except for Viburnum ×burkwoodii and V. ×‘NCVX1’, decreased to various degrees with increasing salinity levels. The Pn, g S, and E of V. ×burkwoodii and V. ×‘NCVX1’ 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, g S, 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, g S, 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.
Ji Jhong Chen, Haifeng Xing, Asmita Paudel, Youping Sun, Genhua Niu, and Matthew Chappell
Youping Sun, Ji Jhong Chen, Haifeng Xing, Asmita Paudel, Genhua Niu, and Matthew Chappell
Viburnums are widely used in gardens and landscapes throughout the United States. Although salinity tolerance varies among plant species, research-based information is limited on the relative salt tolerance of viburnum species. The morphological and growth responses of 12 viburnum taxa to saline solution irrigation were evaluated under greenhouse conditions. Viburnum taxa included Viburnum ×burkwoodii, V. cassinoides ‘SMNVCDD’, V. dentatum ‘Christom’, V. dentatum var. deamii ‘SMVDLS’, V. dilatatum ‘Henneke’, V. ×‘NCVX1’, V. nudum ‘Bulk’, V. opulus ‘Roseum’, V. plicatum var. tomentosum ‘Summer Snowflake’, V. pragense ‘Decker’, V. ×rhytidophylloides ‘Redell’, and V. trilobum. A nutrient solution at an electrical conductivity (EC) of 1.3 dS·m−1 (control) or saline solutions at ECs of 5.0 and 10.0 dS·m−1 were applied eight times over a 9-week period. Growth, visual quality, and morphological characteristics were quantified at the 4th week and 8th–9th week to assess the impact of salinity stress on the viburnum taxa. Saline solution irrigation imposed detrimental salinity stress on viburnum plant growth and visual quality, and the degree of salt damage was dependent on the salinity levels of irrigation solution and the length of exposure to salinity stress as well as viburnum taxa. Viburnum ×burkwoodii and V. ×‘NCVX1’ had little foliar salt damage during the entire experiment, except those irrigated with saline solution at an EC of 10.0 dS·m−1 exhibited slight to moderate foliar salt damage at the eighth week. Viburnum dilatatum ‘Henneke’, V. plicatum var. tomentosum ‘Summer Snowflake’, and V. trilobum irrigated with saline solution at an EC of 5.0 dS·m−1 had slight and severe foliar salt damage at the 4th and 8th week, respectively. Plants irrigated with saline solution at an EC of 10.0 dS·m−1 exhibited severe foliar salt damage at the 4th week, and all died by the 8th week. Other viburnum taxa also showed various foliar salt damage, especially at an EC of 10.0 dS·m−1. The shoot dry weights of V. ×burkwoodii and V. ×‘NCVX1’ irrigated with saline solution at ECs of 5.0 and 10.0 dS·m−1 were similar to those in the control at both harvest dates. However, the shoot dry weight of other tested viburnum taxa decreased to some extent at the 9th week. A cluster analysis concluded that V. ×burkwoodii and V. ×‘NCVX1’ were considered the most salt-tolerant viburnum taxa, whereas V. dilatatum ‘Henneke’, V. plicatum var. tomentosum ‘Summer Snowflake’, and V. trilobum were sensitive to salinity levels used in this study. This research may guide the green industry to choose relatively tolerant viburnum taxa for landscape use and nursery production where low-quality water is used for irrigation.
Haifeng Xing, Julie Hershkowitz, Asmita Paudel, Youping Sun, Ji Jhong Chen, Xin Dai, and Matthew Chappell
Reclaimed water provides a reliable and economical alternative source of irrigation water for landscape use but may have elevated levels of salts that are detrimental to sensitive landscape plants. Landscape professionals must use salt-tolerant plants in regions where reclaimed water is used. Ornamental grasses are commonly used as landscape plants in the Intermountain West of the United States due to low maintenance input, drought tolerance, and unique texture. Six ornamental grass species, including Acorus gramineus (Japanese rush), Andropogon ternarius (silver bluestem), Calamagrostis ×acutiflora (feather reed grass), Carex morrowii (Japanese sedge), Festuca glauca (blue fescue), and Sporobolus heterolepis (prairie dropseed), were evaluated for salinity tolerance. Plants were irrigated every 4 days with a fertilizer solution at an electrical conductivity (EC) of 1.2 dS·m–1 (control) or with a saline solution at an EC of 5.0 dS·m–1 (EC 5) or 10.0 dS·m–1 (EC 10). At 47 days, most species in EC 5 exhibited good visual quality with averaged visual scores greater than 4.6 (0 = dead, 5 = excellent). In EC 10, most A. gramineus plants died, but C. ×acutiflora, F. glauca, and S. heterolepis had no foliar salt damage. At 95 days, C. ×acutiflora, F. glauca, and S. heterolepis in EC 5 had good visual quality with averaged visual scores greater than 4.5. Acorus gramineus, A. ternarius, and C. morrowii showed foliar salt damage with averaged visual scores of 2.7, 3.2, and 3.4, respectively. In EC 10, A. gramineus died, and other grass species exhibited moderate to severe foliar salt damage, except C. ×acutiflora, which retained good visual quality. Plant height, leaf area, number of tillers, shoot dry weight, and/or gas exchange parameters also decreased depending on plant species, salinity level, and the duration of exposure to salinity stress. In conclusion, A. gramineus was the most salt-sensitive species, whereas C. ×acutiflora was the most salt-tolerant species. Festuca glauca and S. heterolepis were more tolerant to salinity than A. ternarius and C. morrowii. Calamagrostis ×acutiflora, F. glauca, and S. heterolepis appear to be more suitable for landscapes in which reclaimed water is used for irrigation. Plant responses to saline water irrigation in this research could also be applied to landscapes in salt-prone areas and coastal regions with saltwater intrusion into aquifers and landscapes affected by maritime salt spray.