Plant materials and growing conditions.

On 2 Mar. 2018, rooted cuttings in 32-cell trays (5.5 × 5.5 × 10.0 cm) of 7 japanese spirea cultivars [Galen (Double Play^® Artisan^® USPP21,712), Minspi (Double Play^® Painted Lady™), NCSX1 (Double Play^® Candy Corn™ USPP28,313), NCSX2 (Double Play Doozie™ USPPAF), SMNSJMFP (Double Play^® Pink USPP26,995), Tracy (Double Play^® Big Bang™ USPP21,588), and Yan (Double Play^® Gold USPP21,615)] were received from Spring Meadow Nursery (Grand Haven, MI). They were grown in a greenhouse in Logan, UT (lat. 41°45′28″N; long. 111°48′47″W; elevation 1409 m), and watered with tap water [electrical conductivity (EC) = 0.36 dS·m⁻¹; pH = 7.95]. The sodium adsorption ratio (SAR) of the tap water was 0.04, and the major ions in the tap water were calcium (Ca²⁺), magnesium (Mg²⁺), sulfate (SO₄²⁻), Cl⁻, Na⁺, and potassium (K⁺) at 47.2, 17.3, 8.9, 3.4, 1.4, and 0.4 mg·L⁻¹, respectively. Three weeks later, plants (≈10 inches tall) were potted in 1-gallon, injection-molded, polypropylene containers (PC1D-4; Nursery Supplies, Orange, CA) filled with a soilless growing substrate consisting of 75% peat moss (Canadian sphagnum peat moss; Sun Gro Horticulture, Agawam, MA), 25% vermiculite (Therm-O-Rock West, Chandler, AZ), and 24.3 g/ft³ white athletic field marking gypsum (92% calcium sulfate dihydrate, 21% calcium, 17% sulfur; Western Mining and Minerals, Bakersfield, CA). All plants were irrigated with tap water until treatments started. The average air temperature in the greenhouse was 26.2 ± 1.9 °C during the day and 19.6 ± 5.0 °C at night. The average daily light integral inside the greenhouse was 17.5 ± 3.6 mol·m⁻²·d⁻¹ during the experiment. From 1 Mar. to 2 May, supplemental lights were provided from 0600 to 2200 hr using 1000-W high-pressure sodium lamps (Hydrofarm, Petaluma, CA) at light intensities of 223 ± 37 µmol·m⁻²·s⁻¹ at canopy level when the light intensity inside the greenhouse was less than 544 µmol·m⁻²·s⁻¹.

Treatments.

A nutrient solution with an EC of 1.2 dS·m⁻¹ was prepared by adding 0.8 g·L⁻¹ 15N–2.2P–12.5K water-soluble fertilizer (Peters Excel 15–5–15 Ca-Mag Special; ICL Specialty Fertilizers, Dublin, OH) to tap water and used as the control. Saline solution with an EC of 3.0 dS·m⁻¹ was prepared by adding 0.46 g·L⁻¹ NaCl and 0.44 g·L⁻¹ calcium chloride (CaCl₂) to the aforementioned nutrient solution, and saline solution with an EC of 6.0 dS·m⁻¹ was prepared by adding 1.25 g·L⁻¹ NaCl and 1.20 g·L⁻¹ CaCl₂ to the nutrient solution. This mixture was used because NaCl is the common salt found in reclaimed water (Niu and Cabrera, 2010), and CaCl₂ is used to forestall potential calcium deficiencies (Carter and Grieve, 2006). The pH of all solutions was adjusted to 6.5 ± 0.1 using nitric acid. Both nutrient and saline solutions were prepared in 100-L tanks; EC was confirmed using an EC meter (LAQUA Twin; Horiba, Kyoto, Japan) before irrigation.

Four weeks after transplanting (27 Apr. 2018), uniform plants were chosen for the experiment and all plants were pruned (≈15 cm tall). From 2 May to 14 June 2018, treatment solutions were applied once per week for 8 weeks. At each irrigation, plants were irrigated with 1 L of treatment solution per plant, resulting in a leaching fraction of ≈24%. Between treatment solution irrigations, plants were irrigated with 300 mL of nutrient solution whenever the substrate surface became dry. Irrigation frequency varied with environmental conditions and treatment solution. Plants with higher salinity need less irrigation because of lower water use resulting from the reduced transpiration and leaf area. On 25 June, all plants were harvested. All plants were sprayed with tebuconazole (Bayer Advanced, Research Triangle Park, NC) to control powdery mildew (Podosphaera xanthii) as needed.

Leachate EC.

The pour-through method described by Cavins et al. (2008) and Wright (1986) was used to determine leachate EC. In brief, a saucer was placed under the container that was drained for 30 min after treatment solution was applied. Then, a total of 100 mL of distilled water was poured on the surface of the substrate to obtain leachate in the saucer. Leachate solution was tested using an EC meter. One plant per treatment per cultivar was chosen for measurement. Leachate EC readings were averaged across cultivars.

Plant growth and visual quality.

Height (centimeter) from the pot rim to the top of the plant and two perpendicular widths (centimeter) were recorded 1 week before harvest. The number of inflorescences was also recorded. At harvest, foliar salt damage was rated by giving a visual score based on a reference scale from 0 to 5: 0 = dead; 1 = severe (more than 90%) foliar damage (salt damage: leaf burn and necrosis); 2 = moderate (50% to 90%) foliar salt damage; 3 = slight (less than 50%) foliar salt damage; 4 = good quality with minimal foliar damage; and 5 = excellent without foliar salt damage (Sun et al., 2015). The foliar salt damage rating did not consider plant size. At harvest, plant shoots were cut at the substrate surface. Leaf area (square centimeter) was determined using an area meter (LI-3100; LI-COR Biosciences, Lincoln, NE). Plant shoots were dried in an oven at 70 °C for 3 d, and shoot dry weight (grams) was determined.

Leaf relative chlorophyll content.

Relative chlorophyll content [soil–plant analysis development (SPAD) reading] was measured using a hand-held chlorophyll meter (SPAD-502 Plus; Minolta Camera Co., Osaka, Japan) 1 week before harvest. The third, fourth, or fifth healthy and fully expanded leaves, counting from the top of the plant downward, were chosen for measurements. Five leaves were measured on each plant and the average number was recorded.

Gas exchange.

Leaf net photosynthetic rate (P_n), stomatal conductance (g_S), transpiration (E), and water use efficiency (WUE) of four plants per treatment per cultivar were measured on 19 and 20 June using a portable photosynthesis system with an automatic universal PLC6 broad leaf cuvette (CIRAS-3; PP Systems, Amesbury, MA). The third, fourth, and fifth healthy and fully expanded leaves, counting from the top of the plant downward, were chosen for measurement. Environmental conditions within the cuvette were maintained at a photosynthetic photon flux of 1000 μmol·m⁻²·s⁻¹ and carbon dioxide concentration of 400 μmol·mol⁻¹. Data were recorded when the environmental conditions and gas exchange rates in the cuvette stabilized. These measurements were performed on sunny days between 1000 and 1400 hr, and plants were watered well the day before to avoid drought stress.

Experimental design and statistical analysis.

The experiment used a completely randomized design with seven plants per treatment per cultivar. Two-way analysis of variance was performed for all plant growth parameters except visual score, which was analyzed using repeated measures for multinomial data. In addition, the number of inflorescences was analyzed as negative binomial data. The mean separation among treatments and cultivars was adjusted using Tukey’s method for multiplicity with α = 0.05. All statistical analyses were performed using the GENMOD and GLIMMIX procedures of SAS/STAT 14.3 in SAS (version 9.4; SAS Institute, Cary, NC).

Visual quality.

All japanese spirea plants had excellent visual quality at 2 weeks after initiating treatments (Fig. 1). At 4 weeks, all plants irrigated with saline solution with an EC of 3.0 dS·m⁻¹ still had excellent visual quality. However, at 4 weeks, foliar salt damage became apparent on japanese spirea plants when irrigated with saline solution with an EC of 6.0 dS·m⁻¹. ‘Yan’ displayed moderate foliar salt damage, with 65% of plants having visual scores more than 2; ‘Tracy’ exhibited slight foliar salt damage, with 93% of plants having visual scores of 3 or more, and ‘Minspi’ and ‘NCSX2’ had minimal foliar salt damage, with 91% and 95%, respectively, of plants rated greater than 4. All ‘Galen’, ‘NCSX1’, and ‘SMNSJMFP’ japanese spirea irrigated with saline solution with an EC of 6.0 dS·m⁻¹ had visual scores of 5.

Visual score of seven japanese spirea cultivars irrigated with a nutrient solution with an electrical conductivity (EC) of 1.2 dS·m⁻¹ (control) or a saline solution with an EC of 3.0 dS·m⁻¹ (EC3) or 6.0 dS·m⁻¹ (EC6) in a greenhouse. Saline solution was created by adding sodium chloride (NaCl) and calcium chloride (CaCl₂) to the nutrient solution. Plants were harvested after the eighth irrigation (8 weeks after initiating treatment). 0 = dead; 1 = severe (more than 90%) foliar salt damage (salt damage: leaf burn and necrosis); 2 = moderate (50% to 90%) foliar salt damage; 3 = slight (less than 50%) foliar salt damage; 4 = good quality with minimal foliar salt damage; and 5 = excellent without foliar salt damage (Sun et al., 2015). 1 dS·m⁻¹ = 1 mmho/cm.

Citation: HortTechnology hortte 29, 3; 10.21273/HORTTECH04280-19

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Visual score of seven japanese spirea cultivars irrigated with a nutrient solution with an electrical conductivity (EC) of 1.2 dS·m⁻¹ (control) or a saline solution with an EC of 3.0 dS·m⁻¹ (EC3) or 6.0 dS·m⁻¹ (EC6) in a greenhouse. Saline solution was created by adding sodium chloride (NaCl) and calcium chloride (CaCl₂) to the nutrient solution. Plants were harvested after the eighth irrigation (8 weeks after initiating treatment). 0 = dead; 1 = severe (more than 90%) foliar salt damage (salt damage: leaf burn and necrosis); 2 = moderate (50% to 90%) foliar salt damage; 3 = slight (less than 50%) foliar salt damage; 4 = good quality with minimal foliar salt damage; and 5 = excellent without foliar salt damage (Sun et al., 2015). 1 dS·m⁻¹ = 1 mmho/cm.

Citation: HortTechnology hortte 29, 3; 10.21273/HORTTECH04280-19

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Visual score of seven japanese spirea cultivars irrigated with a nutrient solution with an electrical conductivity (EC) of 1.2 dS·m⁻¹ (control) or a saline solution with an EC of 3.0 dS·m⁻¹ (EC3) or 6.0 dS·m⁻¹ (EC6) in a greenhouse. Saline solution was created by adding sodium chloride (NaCl) and calcium chloride (CaCl₂) to the nutrient solution. Plants were harvested after the eighth irrigation (8 weeks after initiating treatment). 0 = dead; 1 = severe (more than 90%) foliar salt damage (salt damage: leaf burn and necrosis); 2 = moderate (50% to 90%) foliar salt damage; 3 = slight (less than 50%) foliar salt damage; 4 = good quality with minimal foliar salt damage; and 5 = excellent without foliar salt damage (Sun et al., 2015). 1 dS·m⁻¹ = 1 mmho/cm.

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At 6 weeks, all japanese spirea plants irrigated with saline solution with an EC of 3.0 dS·m⁻¹ showed good or excellent visual quality except ‘Yan’. ‘Yan’ exhibited minimal foliar salt damage, with 90% of plants rated 4 or 5 (Fig. 1). With an EC of 6.0 dS·m⁻¹, 32% and 65% of ‘Tracy’ and ‘Yan’ plants died, respectively, and 33% and 24% of plants exhibited severe foliar salt damage, with a visual score of 1. ‘Minspi’ showed moderate foliar salt damage, with 91% of plants with visual scores more than 2. ‘NCSX1’ and ‘NCSX2’ had slight foliar salt damage, with more than 84% of plants with visual scores of 3 or more. ‘Galen’ and ‘SMNSJMFP’ still had excellent visual quality, with 91% and 99%, respectively, of plants with ratings of 4 or 5. Visual quality of ‘Galen’ and ‘SMNSJMFP’ was significantly better than that of ‘Tracy’, ‘Yan’, ‘Minspi’, ‘NCSX1’, and ‘NCSX2’ (P < 0.05).

At 8 weeks, the impact of saline irrigation water on plant aesthetic quality became remarkably worse (Fig. 1). When irrigated with saline solution with an EC of 3.0 dS·m⁻¹, ‘Tracy’ and ‘Yan’ plants exhibited slight-to-moderate foliar salt damage. The remaining five japanese spirea cultivars had good or excellent visual quality with ratings of 4 or 5. No ‘Tracy’ and ‘Yan’ plants survived when irrigated with saline solution with an EC of 6.0 dS·m⁻¹. This treatment also caused 75% and 25% plant death in ‘NCSX2’ and ‘Minspi’, respectively. For these two cultivars, less than 5% of plants maintained good or excellent visual quality. Foliar salt damage was less severe in ‘NCSX1’, with 42% of plants having good or excellent visual quality, which was significantly greater than that of ‘NCSX2’ and ‘Minspi’ (P < 0.05). Although ‘Galen’ had better visual appearance than ‘NCSX1’ at 6 weeks after initiating treatment, they did not differ at 8 weeks after treatment was initiated (P = 0.51). Approximately 36% of ‘Galen’ plants had good or excellent visual quality. SMNSJMFP appeared to be the most salt-tolerant cultivar in terms of visual quality. The mortality rate of this cultivar was consistently less than 1%, whereas 64% of plants had good or excellent visual quality with ratings of 4 or 5. In addition, ‘SMNSJMFP’ plants irrigated with saline solution with an EC 6.0 dS·m⁻¹ outperformed other cultivars (P < 0.05).

It appeared that ‘Tracy’ and ‘Yan’ japanese spirea were sensitive to saline irrigation water applied in the study, whereas ‘SMNSJMFP’ and ‘Galen’ japanese spirea were relatively salt-tolerant. High salinity is known to cause plant injuries such as leaf necrosis, burn, and premature discoloration, which lead to poor visual quality and poor marketability of ornamental plants (Chen et al., 2017; Sun et al., 2018). In this study, the substrate EC values gradually increased with the irrigation of saline solution (Fig. 2). The average leachate EC of plants irrigated with nutrient solution increased from 1.13 to 5.27 dS·m⁻¹, whereas irrigation with saline solution with EC values of 3.0 and 6.0 dS·m⁻¹ resulted in the average leachate EC values increasing from 1.85 to 9.94 dS·m⁻¹ and from 3.39 to 12.98 dS·m⁻¹, respectively. The EC values of the leachate collected from the nutrient solution irrigation were consistently lower than those of the leachate from saline solution irrigations after the second irrigation. This is why foliar salt damage changed over time and differed among saline water irrigations.

Leachate electrical conductivity (EC) during the experimental period. Control denotes nutrient solution with an EC of 1.2 dS·m⁻¹, whereas EC3 and EC6 denote saline solutions with an EC of 3.0 dS·m⁻¹ and 6.0 dS·m⁻¹, respectively. Saline solution was created by adding sodium chloride (NaCl) and calcium chloride (CaCl₂) to the nutrient solution. Leachate EC readings were averaged across seven japanese spirea cultivars. Error bars represent the sd of seven measurements. 1 dS·m⁻¹ = 1 mmho/cm.

Citation: HortTechnology hortte 29, 3; 10.21273/HORTTECH04280-19

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Leachate electrical conductivity (EC) during the experimental period. Control denotes nutrient solution with an EC of 1.2 dS·m⁻¹, whereas EC3 and EC6 denote saline solutions with an EC of 3.0 dS·m⁻¹ and 6.0 dS·m⁻¹, respectively. Saline solution was created by adding sodium chloride (NaCl) and calcium chloride (CaCl₂) to the nutrient solution. Leachate EC readings were averaged across seven japanese spirea cultivars. Error bars represent the sd of seven measurements. 1 dS·m⁻¹ = 1 mmho/cm.

Citation: HortTechnology hortte 29, 3; 10.21273/HORTTECH04280-19

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Leachate electrical conductivity (EC) during the experimental period. Control denotes nutrient solution with an EC of 1.2 dS·m⁻¹, whereas EC3 and EC6 denote saline solutions with an EC of 3.0 dS·m⁻¹ and 6.0 dS·m⁻¹, respectively. Saline solution was created by adding sodium chloride (NaCl) and calcium chloride (CaCl₂) to the nutrient solution. Leachate EC readings were averaged across seven japanese spirea cultivars. Error bars represent the sd of seven measurements. 1 dS·m⁻¹ = 1 mmho/cm.

Citation: HortTechnology hortte 29, 3; 10.21273/HORTTECH04280-19

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Growth index and leaf area.

Saline water irrigation affected plant growth of japanese spirea, as indicated by the growth index and leaf area, and all cultivars responded similarly (Fig. 3). Compared with the control, the average growth index values of all japanese spirea cultivars irrigated with saline solution with EC values of 3.0 and 6.0 dS·m⁻¹ decreased by 4% and 12%, respectively. The average leaf area of all japanese spirea cultivars irrigated with saline solution with EC values of 3.0 and 6.0 dS·m⁻¹ decreased by 21% and 49%, respectively. Similarly, stunted growth and reduction in leaf area have been observed in many ornamental plants irrigated with saline water (Chen et al., 2017; Liu et al., 2017; Sun et al., 2018). This might be caused by a salt-induced water deficit because salinity lowers the water potential of soil solution, thus making water less available to plants. Turgor-dependent activities such as stem elongation and leaf expansion are the most sensitive to water deficits (Taiz and Zeiger, 2015). Additionally, as an adaptation to a saline environment, the salt-induced water deficit stimulates leaf abscission that could significantly reduce transpiration and water loss. ‘SMNSJMFP’ japanese spirea had the greatest growth index and leaf area, whereas ‘Yan’ had the smallest growth index and leaf area (Fig. 3). This is because all japanese spirea cultivars tested in this study have different plant growth habits. ‘Galen’, ‘Minspi’, ‘NCSX2’, ‘SMNSJMFP’, and ‘Tracy’ japanese spirea have a compact, mounded shape and are 2- to 3-ft tall and wide (Monrovia, 2018b; Morton Arboretum, 2018; Proven Winners, 2018a, 2018b; Spring Meadow Nursery, 2018), whereas ‘NCSX1’ and ‘Yan’ japanese spirea are exceptional low-growing shrubs that are 1- to 2-ft tall and wide (Monrovia, 2018a; Morton Arboretum, 2018).

The growth index [(height + width 1 + width 2)/3] (A) and leaf area (B) of seven japanese spirea cultivars irrigated with a nutrient solution with an electrical conductivity (EC) of 1.2 dS·m⁻¹ (control) or a saline solution with an EC of 3.0 dS·m⁻¹ (EC3) or 6.0 dS·m⁻¹ (EC6) in a greenhouse. Saline solution was created by adding sodium chloride (NaCl) and calcium chloride (CaCl₂) to the nutrient solution. Same uppercase letters above the error bars are not significantly different among cultivars or treatments with Tukey’s multiple comparison (α = 0.05). 1 dS·m⁻¹ = 1 mmho/cm; 1 cm = 0.3937 inch; 1 cm² = 0.1550 inch².

Citation: HortTechnology hortte 29, 3; 10.21273/HORTTECH04280-19

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The growth index [(height + width 1 + width 2)/3] (A) and leaf area (B) of seven japanese spirea cultivars irrigated with a nutrient solution with an electrical conductivity (EC) of 1.2 dS·m⁻¹ (control) or a saline solution with an EC of 3.0 dS·m⁻¹ (EC3) or 6.0 dS·m⁻¹ (EC6) in a greenhouse. Saline solution was created by adding sodium chloride (NaCl) and calcium chloride (CaCl₂) to the nutrient solution. Same uppercase letters above the error bars are not significantly different among cultivars or treatments with Tukey’s multiple comparison (α = 0.05). 1 dS·m⁻¹ = 1 mmho/cm; 1 cm = 0.3937 inch; 1 cm² = 0.1550 inch².

Citation: HortTechnology hortte 29, 3; 10.21273/HORTTECH04280-19

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The growth index [(height + width 1 + width 2)/3] (A) and leaf area (B) of seven japanese spirea cultivars irrigated with a nutrient solution with an electrical conductivity (EC) of 1.2 dS·m⁻¹ (control) or a saline solution with an EC of 3.0 dS·m⁻¹ (EC3) or 6.0 dS·m⁻¹ (EC6) in a greenhouse. Saline solution was created by adding sodium chloride (NaCl) and calcium chloride (CaCl₂) to the nutrient solution. Same uppercase letters above the error bars are not significantly different among cultivars or treatments with Tukey’s multiple comparison (α = 0.05). 1 dS·m⁻¹ = 1 mmho/cm; 1 cm = 0.3937 inch; 1 cm² = 0.1550 inch².

Citation: HortTechnology hortte 29, 3; 10.21273/HORTTECH04280-19

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Number of inflorescences and total dry weight.

‘NCSX1’, ‘NCSX2’, and ‘Tracy’ plants had no flowers during the entire experiment (Table 1). The number of inflorescences of ‘Minspi’ and ‘Yan’ irrigated with saline water with an EC of 3.0 dS·m⁻¹ was similar to that of the control. However, ‘Galen’ and ‘SMNSJMFP’ plants had 34% fewer inflorescences than the control. When irrigated with saline solution with an EC of 6.0 dS·m⁻¹, the inflorescences of ‘Galen’, ‘Minspi’, and ‘SMNSJMFP’ were reduced by 39%, 50%, and 40%, respectively. Compared with the control, the shoot dry weight of ‘Galen’, ‘Minspi’, ‘SMNSJMFP’, and ‘Yan’ irrigated with saline solution with an EC of 3.0 dS·m⁻¹ decreased by 27%, 22%, 28%, and 35%, respectively (Table 1). The shoot dry weights of ‘NCSX1’, ‘NCSX2’, and ‘Tracy’ plants irrigated with saline solution with an EC of 3.0 dS·m⁻¹ were similar to that of the control. All japanese spirea cultivars irrigated with saline solution with an EC of 6.0 dS·m⁻¹ had 35% to 56% lower shoot dry weights than the control. Increased salinity reduced shoot dry weight in a variety of plant species (Chen et al., 2017; Liu et al., 2017; Sun et al., 2015, 2018). The reduced shoot growth of japanese spirea plants observed in this study should have resulted from the salts accumulated in plant root zone, as indicated by the EC values of the leachate solution collected immediately after irrigation (Fig. 2). Due to plant growth habits, SMNSJMFP’ and ‘Galen’ japanese spirea had the greatest shoot dry weight, whereas ‘Minspi’ had the lowest shoot dry weight (Table 1).

Table 1.

Number of inflorescences and shoot dry weight of seven japanese spirea cultivars irrigated with a nutrient solution with an electrical conductivity (EC) of 1.2 dS·m⁻¹ (control) or a saline solution with an EC of 3.0 dS·m⁻¹ (EC3) or 6.0 dS·m⁻¹ (EC6) in a greenhouse. Saline solution was created by adding sodium chloride (NaCl) and calcium chloride (CaCl₂) to the nutrient solution. Plants were harvested after the eighth irrigation (8 weeks after initiating treatment).^z

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Relative chlorophyll content (SPAD) and gas exchange.

Increased salinity did not affect the SPAD readings of ‘Galen’, ‘NCSX1’, and ‘Tracy’ (Table 2). Saline solution with an EC of 3.0 dS·m⁻¹ decreased the SPAD readings of ‘NCSX2’, ‘Minspi’, and ‘Yan’ by 11%, 14%, and 27%, respectively, compared with that of the control. The SPAD readings of ‘Minspi’ and ‘SMNSJMFP’ decreased by 16% and 15%, respectively, when they were irrigated with saline solution with an EC of 6.0 dS·m⁻¹. Compared with the control, the P_n of ‘Galen’, ‘NCSX1’, ‘NCSX2’, and ‘Tracy’ irrigated with saline solution with an EC of 3.0 dS·m⁻¹ decreased by 20% to 37%; however, that of ‘Yan’ decreased by 57% (Table 2). Saline solution with an EC of 6.0 dS·m⁻¹ further reduced the P_n of ‘Galen’, ‘NCSX1’, and ‘NCSX2’ by 41%, 47%, and 52%, respectively. The P_n of ‘Minspi’ and ‘SMNSJMFP’ irrigated with saline solution with an EC of 3.0 dS·m⁻¹ were similar to that of the control, but saline solution with an EC of 6.0 dS·m⁻¹ decreased the P_n of ‘Minspi’ and ‘SMNSJMFP’ by 56% and 44%, respectively. The negative impact of salinity on plant photosynthesis has been reported previously (Liu et al., 2017; Sun et al., 2015). High concentrations of Na⁺ and/or Cl⁻ in chloroplasts might lead to the decrease in photosynthesis (Taiz and Zeiger, 2015).

Table 2.

The relative chlorophyll content (SPAD) and photosynthetic rate (P_n) of seven japanese spirea cultivars irrigated with a nutrient solution with an electrical conductivity (EC) of 1.2 dS·m⁻¹ (control) or a saline solution with an EC of 3.0 dS·m⁻¹ (EC3) or 6.0 dS·m⁻¹ (EC6) in a greenhouse. Saline solution was created by adding sodium chloride (NaCl) and calcium chloride (CaCl₂) to the nutrient solution.^z

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The g_S, transpiration rate, and water use efficiency of japanese spirea were impacted by saline water irrigation, and all cultivars showed similar responses (Fig. 4). The g_S and transpiration rate of japanese spirea plants irrigated with saline solution with an EC of 3.0 dS·m⁻¹ was similar to that of the control. However, the water use efficiency of japanese spirea irrigated with saline solution with an EC of 3.0 dS·m⁻¹ decreased by 17% compared with the control. Saline irrigation water with an EC of 6.0 dS·m⁻¹ further reduced the g_S, transpiration rate, and water use efficiency of japanese spirea by 14%, 38%, and 13%, respectively. These results are in line with previous reports that indicated that increased salinity negatively impacts plant g_S and transpiration rates (Liu et al., 2017; Sun et al., 2015).

The stomatal conductance (A), transpiration rate (B), and water use efficiency (C) of seven japanese spirea cultivars irrigated with a nutrient solution with an electrical conductivity (EC) of 1.2 dS·m⁻¹ (control) or a saline solution with an EC of 3.0 dS·m⁻¹ (EC3) or 6.0 dS·m⁻¹ (EC6) in a greenhouse. Saline solution was created by adding sodium chloride (NaCl) and calcium chloride (CaCl₂) to the nutrient solution. Same uppercase letters above the error bars are not significantly different among cultivars or treatments with Tukey’s multiple comparison (α = 0.05). 1 dS·m⁻¹ = 1 mmho/cm; 1 m² = 10.7639 ft².

Citation: HortTechnology hortte 29, 3; 10.21273/HORTTECH04280-19

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The stomatal conductance (A), transpiration rate (B), and water use efficiency (C) of seven japanese spirea cultivars irrigated with a nutrient solution with an electrical conductivity (EC) of 1.2 dS·m⁻¹ (control) or a saline solution with an EC of 3.0 dS·m⁻¹ (EC3) or 6.0 dS·m⁻¹ (EC6) in a greenhouse. Saline solution was created by adding sodium chloride (NaCl) and calcium chloride (CaCl₂) to the nutrient solution. Same uppercase letters above the error bars are not significantly different among cultivars or treatments with Tukey’s multiple comparison (α = 0.05). 1 dS·m⁻¹ = 1 mmho/cm; 1 m² = 10.7639 ft².

Citation: HortTechnology hortte 29, 3; 10.21273/HORTTECH04280-19

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The stomatal conductance (A), transpiration rate (B), and water use efficiency (C) of seven japanese spirea cultivars irrigated with a nutrient solution with an electrical conductivity (EC) of 1.2 dS·m⁻¹ (control) or a saline solution with an EC of 3.0 dS·m⁻¹ (EC3) or 6.0 dS·m⁻¹ (EC6) in a greenhouse. Saline solution was created by adding sodium chloride (NaCl) and calcium chloride (CaCl₂) to the nutrient solution. Same uppercase letters above the error bars are not significantly different among cultivars or treatments with Tukey’s multiple comparison (α = 0.05). 1 dS·m⁻¹ = 1 mmho/cm; 1 m² = 10.7639 ft².

Citation: HortTechnology hortte 29, 3; 10.21273/HORTTECH04280-19

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