No abstract

The effect of drought on the growth and gas exchange of six bedding plant species—agastache [Agastache urticifolia (Benth.) O. Kuntze `Honeybee Blue'], dusty miller (Cineraria maritima L. `Silverdusty'), petunia (Petunia ×hybrida `Wave Purple'), plumbago (Plumbago auriculata Lam. `Escapade'), ornamental pepper (Capsicum annuum L. `Black Pearl'), and vinca [Catharanthus roseus (L.) G. Don `Titan']—was quantified under greenhouse conditions. Seeds were sown in January and seedlings were grown in the greenhouse until 18 Apr., when two irrigation treatments—drought (D, ≈18% volumetric moisture content at reirrigation) and control (C, ≈25% volumetric moisture content at reirrigation)—were initiated. Leaf net photosynthetic rate (Pn), stomatal conductance (gs), and transpiration (E) were determined in response to a range of substrate moisture content (from ≈5% to 30% by volume) and temperature (from 20 °C to 40 °C). Dry weight of agastache, ornamental pepper, and vinca was unaffected by drought, whereas that of other species was reduced. Leaf area of plumbago and height of plumbago and vinca were reduced by drought. As substrate moisture content decreased from 25% to 10%, Pn, E, and gs decreased linearly in all species except petunia and plumbago. Leaf net photosynthetic rate of all species declined as leaf temperature increased from 20 °C to 40 °C. In contrast, E of all species, except petunia, increased as temperature increased. Transpiration rate of petunia increased as temperature increased from 20 °C to 30 °C, and then decreased between 30 °C and 40 °C. Although petunia had the highest Pn among the tested species, its Pn and gs declined more rapidly compared with the other species as temperature increased from 20 °C to 40 °C or as substrate moisture content decreased, indicating that petunia was most sensitive to high temperature and drought.

Use of recycled water to irrigate urban landscapes may be inevitable, because the freshwater supply has been diminishing and the population continues to grow in the arid and semiarid southwestern United States. However, little information exists on the performance of landscape plants irrigated with nonpotable water. Two greenhouse studies were conducted during the summer and the fall to characterize the relative salt tolerance of five herbaceous perennials by irrigating the plants with a saline solution at an electrical conductivity (EC) of 0.8 dS·m–1 (tap water), 2.0 dS·m–1, or 4.0 dS·m–1. In the summer study, after 10 weeks of treatment, Achillea millefolium L., Gaillardia aristata Foug., and Salvia coccinea Juss ex J. had an aesthetically acceptable appearance for landscape performance (visual quality scores of 4 points or more), whereas Agastache cana (Hook.) Woot. & Standl. and Echinacea purpurea (L.) Moench had relatively low tolerance to salinity. Dry weight of shoots of A. millefolium, A. cana, and G. arstata was lower at elevated salinity levels. In the fall study, A. millefolium, E. purpurea, G. arstata, and S. coccinea had acceptable growth and visual quality at elevated salinity levels, whereas A. cana had lower quality and reduced growth. Dry weight of shoots was lower in G. arstata and A. millefolium at an EC of 2.0 dS·m–1 or 4.0 dS·m–1. Leaf osmotic potential of all species in the summer experiment was significantly lower at higher salinity compared with the control. In the fall experiment, leaf osmotic potential in A. millefolium, E. purpurea, and G. aristata at 4 dS·m–1 was lower compared with lower salinity treatment and the control. Leaf osmotic potential in the fall was higher than that of the same species at the same salinity level in the summer experiment, indicating that plants in the fall were less stressed than in the summer. Combined the results from both experiments, the authors concluded that A. millefolium, G. arstata, and S. coccinea had a relatively high salt tolerance (as much as 4 dS·m–1 of irrigation water under greenhouse conditions) among the tested species, whereas A. cana and E. purpurea were not tolerant to salt and should not be irrigated with low-quality water.

The growth and physiological responses of four maize inbred lines (CUBA1, B73, B5C2, and BR1) and four sorghum hybrids (SS304, NK7829, Sordan 79, and KS585) to salinity were determined. Fifteen days after sowing, seedlings were irrigated with nutrient solution (control) at electrical conductivity (EC) of 1.5 dS m−1or saline solution at EC of 8.0 dS m−1(salt treatment) for 40 days. Dry weight of shoots in maize was reduced by 58%, 65%, 62%, and 69% in CUBA1, B73, B5C2, and BR1, respectively, while that of sorghum was reduced by 51%, 56%, 56%, and 76% in SS304, NK7829, Sordan79, and KS585, respectively, in the salt treatment compared to their respective control. Salinity stress reduced all or some of the gas exchange parameters, leaf transpiration (E), stomatal conductance (gs), and net photosynthetic rate (Pn) in the late part of the experiment for both crops. Salinity treatment greatly increased Na+uptake in all maize genotypes but did not affect the Na+uptake in sorghum, regardless of genotype. In maize, CUBA1 was slightly more resistant to salt stress, while BR1 was more sensitive to salt stress. In sorghum, Sordan79 was the most tolerant genotype, and KS585 was the least tolerant genotype.

As high-quality water supply becomes limited in many regions of the world, alternative water sources are being used for irrigating urban landscapes. Therefore, salt-tolerant landscape plants are needed. Two greenhouse experiments were conducted to screen the salt tolerance of Zinnia marylandica (‘Zahara Coral Rose’, ‘Zahara Fire’, ‘Zahara Scarlet’, ‘Zahara Starlight’, ‘Zahara White’, and ‘Zahara Yellow’) and Z. maritima ‘Solcito’. In Expt. 1, plants were subirrigated with nutrient or saline solutions at electrical conductivity (EC) at 1.4 (base nutrient solution, control), 3.0, 4.2, 6.0, or 8.2 dS·m−1 for 4 weeks, whereas in Expt. 2, plants were surface-irrigated with the same nutrient or saline solutions for 4 weeks. In Expt. 1, all plants, regardless of cultivar, died by the end of the treatment at EC 6.0 and EC 8.2 as a result of high salinity in the root zone. Plants became shorter and more compact as EC of irrigation water increased. Shoot dry weight of all cultivars in EC 4.2 was reduced by 50% to 56% compared with that of the control. Shoot Na+ and Cl– accumulated excessively as salinity increased in the irrigation water, whereas Ca2+, Mg2+, and K+ did not change substantially. In Expt. 2, mortality varied with cultivar and treatment. Similar to Expt. 1, growth reduction resulting from elevated salinity across cultivars was found. Therefore, it is concluded that zinnia cultivars used in this study are sensitive to salinity and should not be planted in areas with high soil salinity or when alternative waters with high salinity may be used for irrigation.