Live oak trees raised from acorns are highly non-uniform and many produce numerous undesirable rhizomic shoots. The objectives of this study were to 1) compare the growth rates between (Quercus virginiana Mill.) trees from seed and cutting in four production systems and 2) determine if trees from cuttings produce rhizomic shoots. Rhizomic shoot cuttings 25–30 cm long were taken from a single tree about 50 years old in late Aug. 1990, rooted, and planted in 2.6-L pots after 2 months. During the same week, acorns were collected from the same tree and germinated. All trees were planted into 13-L pots in July 1991 and then to a field in July 1992. Trees from both sources were planted either directly in the ground, in 36.6- or 45.7-cm-diameter polypropylene fabric bags buried in the ground, or in 13-L pots on the ground. Trunk circumference 10 cm above the soil line was roughly measured yearly between 1992 and 1999. Initially, trees from cuttings grew slightly slower than seedlings, having a smaller trunk circumference, diameter, and cross-sectional area. These differences diminished and all trees had similar circumferences after 1996. In 1992, trees in 36.6-cm bags and pots had more growth than trees in the ground. In 1993, trees in pots had better growth than those in the ground. After 1993, all trees had similar circumferences until the end of this study, probably due to roots extending beyond the bags and pots into the surrounding soil. About one-third of the seedling trees produced rhizomic shoots, whereas none of the trees from cuttings did. The rhizomic shoots of trees in pots were contained within the pot and none from the ground. Another significance of this research is that the cloned trees from cuttings were extremely uniform in growth habit and form.
Yin-Tung Wang and Genhua Niu
Genhua Niu and Denise S. Rodriguez
Salvia greggii (salvia) and Dalea frutescens (dalea) are two popular shrubs. However, little information is available on their drought tolerance. The objectives of this study were to investigate the effect of various degrees of water stress on growth and to characterize the dynamics of water relations to root substrate water content for developing best irrigation management. Salvia and dalea plants in 12-L plastic containers were grown in a greenhouse and pruned to one node at the base of the soft shoots for salvia or at the same height for dalea prior to the start of the experiment. There were three irrigation regimens: plants were irrigated daily (control), or irrigation was withheld until moderate or severe water stress signs exhibited. After several weeks of intermittent cyclic dry-down irrigation regimens, total shoot number per container was reduced by 40% to 50% for salvia and 35% to 40% for dalea. Average shoot length was reduced by 35% to 45% for salvia and 50% to 65% for dalea in moderate and severe stressed treatments compared to the control. Drought stress resulted in less shoot elongation and fewer new shoots in both species. To examine the relationship between plant water status and substrate water content, a dry down test was performed on five well-watered plants by withholding irrigation until midday water potential dropped to below –4 MPa. As substrate water contents in both species reached 8%, the predawn water potentials did not recover from the midday water potential of the previous day, indicating there was no available water in the substrate for roots to take up. The drought tolerance of these two species needs further study using various growing media.
Genhua Niu and Denise S. Rodriguez
In order to use reclaimed water to irrigate landscape plants and minimize damage and loss, salinity tolerance of commonly used landscape plants needs to be identified and characterized. Eight herbaceous perennials and groundcovers were obtained from a nursery, transplanted to 2.6-L plastic containers, and grown in the greenhouse for 2 weeks before salinity treatments (1.0, 3.2, 6.4, and 12 dS·m-1) were initiated. Plants were irrigated with measured amounts of saline solutions to obtain a 30% leaching when ≈50% water was depleted. After 12 weeks, half of the plants in each treatment were destructively harvested and dry weights of shoots and roots were taken. Three Penstemon species (pseudospectabilis, eatoni, and strictus) and Lavandula angustifoliaat 6.4 and 12 dS·m-1 and most of them at 3.2 dS/m did not survive. Shoot dry weight of Delosperma cooperidecreased by 25% at 12 dS·m–1, but there were no significant differences among the rest of the treatments. All plants of Teucrium chamaedryssurvived, but growth was reduced significantly with lower visual scores as salinity of irrigation water increased. Although growth was reduced in Gazaniarigensas salinity increased, no other signs of stress were observed. Ceratostigma plumbaginoides had less growth at 3.2 dS·m–1, and older leaves showed reddish pigmentation at 6.4 dS·m-1, whereas those at 12 dS·m-1 did not survive. Among the tested species, D.cooperiand G.rigensindicated a high tolerance to salinity; T. chamaedrysand C. plumbaginoides were moderately tolerant; and the rest were salt sensitive.
Genhua Niu and Denise S. Rodriguez
Gaillardia aristata Foug. is a hardy, drought-tolerant perennial found throughout much of the United States. Little information exists on the salt tolerance of this plant when grown in various growing media. A study was conducted to characterize the response of G. aristata to three salinity levels (0.8, 2.0, or 4.0 dS/m) and four growing media: 1) 100% perlite; 2) 1 perlite: 1 Sunshine mix No. 4 (v/v); 3) 100% Sunshine mix No. 4; or 4) 1 Sunshine mix No. 4: 1 composted mulch (v/v). The type of medium influenced the dry weight of roots but not shoots, while salinity significantly influenced the dry weight of both shoots and roots. The dry weight of shoots was higher in plants irrigated with tap water (0.8 dS/m) compared to those irrigated with saline solution at 2.0 or 4.0 dS/m except for those grown in 100% Sunshine mix. The ratio of root to shoot dry weight was not influenced by salinity, but was highest in the plants grown in 100% perlite. Both medium and salinity affected plant height. Elevated salinity reduced plant height. Plants were taller when grown in 100% perlite and in 1 Sunshine mix: 1 composted mulch. However, plants had fewer lateral shoots when grown in 100% perlite or 1 Sunshine mix: 1 composted mulch. Some of the flower buds aborted when grown in 100% Sunshine mix or 1 perlite: 1 Sunshine mix compared to none in plants grown in 100% perlite or 1 Sunshine mix: 1 composted mulch. These results indicate that growth and morphology of G. aristata were affected by not only salinity, but also the type of medium.
Genhua Niu and Denise S. Rodriguez
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.
Genhua Niu and Raul I. Cabrera
Water shortages and poor water quality are critical issues in many areas of the world. With rapid increases in population and shortage of water supplies in urban areas, use of alternative water sources such as municipal reclaimed water and other sources of non-potable waters for irrigating landscapes is inevitable. A potential concern is the elevated salt levels in these alternative waters. This article briefly summarizes general information regarding alternative water sources and general responses of landscape plants to salinity stress. Methodology of screening and evaluating salt tolerance of landscape plants are discussed. Recent research results on salt tolerance of landscape plants and their physiological responses to salinity stress are reviewed. Like agricultural crops, a wide range of salt tolerance among landscape plants has been found. In addition to plant species, dominant salt type, substrate, irrigation method and management, and environmental conditions also affect plant responses to salinity stress. A number of mechanisms of salinity tolerance have been observed among landscape species, including restriction of ion uptake, selective ion uptake, and tolerance to high internal concentrations of sodium and/or chloride.
Genhua Niu and Denise S. Rodriguez
Salt-tolerant garden roses (Rosa L.) are needed for arid and semiarid regions where high-quality water supply is limited and soil salinization often occurs. This greenhouse study evaluated growth, ion uptake characteristics, and the daily evapotranspiration rate (ET) of four rose rootstocks [‘Dr. Huey’ (Rosa ×hybrida L.), R. ×fortuniana Lindl., R. multiflora Thunb., and R. odorata (Andr.) Sweet] irrigated with saline solutions with chloride or sulfate as the dominant salts. After 16 weeks of treatment, the elevated salinities reduced growth of all rootstocks, but the magnitude varied with the rootstock and dominant salt type. At moderate [3.9 dS·m−1 electrical conductivity (EC)] and high salinities (7.9 to 8.2 dS·m−1), chloride-dominated salinity led to a greater growth reduction in R. × fortuniana, followed by R. odorata and R. multiflora. At high salinity dominated by sulfate, R. odorata had a greater growth reduction, followed by R. multiflora, ‘Dr. Huey’, and R. ×fortuniana. For R. multiflora, growth was reduced more in chloride-dominated salinity at high salinity levels, but no differences were found in the growth between the two salt types at moderate salinity. Rosa multiflora accumulated more Na than R. odorata, and R. ×fortuniana accumulated the least. However, R. multiflora retained most the Na in the roots, whereas R. odorata transported 57% of the Na to shoots. All rootstocks had a similar high leaf Cl concentration at high salinity dominated by chloride, while R. ×fortuniana had the most severe foliar salt damage, indicating that R. ×fortuniana had a lower threshold concentration of tissue Cl. At moderate salinity, all rootstocks had acceptable visual quality. At high salinity, the appearance of all rootstocks declined with typical salt damage on lower, older leaves, and the plants had lower visual scores in chloride-dominated salinity, especially in R. ×fortuniana. Salinity treatment did not affect the daily ET per unit leaf area, regardless of rootstock and dominant salt type. Daily ET per pot was the smallest in R. ×fortuniana among the four rootstocks due to its smaller total leaf area. The four rootstocks responded differently to salinity and dominant salt type.
Genhua Niu and Denise S. Rodriguez
Drought-tolerant garden roses (Rosa spp.) are needed in arid and semiarid regions where irrigation water is scarce. The vast majority of garden rose cultivars are budded or grafted onto rootstocks and are seldom grown on their own roots. The objective of this study was to compare the growth and physiological responses of four rose rootstocks to drought stress. Rosa ×hybrida ‘Dr. Huey’, R. ×fortuniana, R. multiflora, and R. odorata grown in 12-L containers were well-irrigated throughout the experiment or were subjected to mild drought stress for five or six cycles, depending on rootstocks, over 10 weeks. Following the mild drought stress cycles, plants that received the mild drought treatment were subjected to a severe dry-down before termination of the experiment. In R. ×fortuniana, drought stress did not affect any growth parameter. Compared with the well-irrigated plants, shoot dry weight of ‘Dr. Huey’, R. multiflora, and R. odorata were reduced by 22%, 33%, and 38%, respectively, by the drought treatment. The final leaf area of R. multiflora and R. odorata was reduced by 42% and 59%, respectively, compared with the control plants. The final leaf area of ‘Dr. Huey’ was not influenced by the drought treatment. Root to shoot ratio in ‘Dr. Huey’ was unaffected, while that of R. multiflora and R. odorata increased as a result of the drought treatment. As substrate moisture content decreased, leaf relative water content (RWC) of all rootstocks decreased linearly, with differences in decreasing slope or intercept of the linear regression lines among rootstocks. Predawn leaf water potential during the dry-down began to decrease rapidly when substrate moisture content decreased to below 20% (25% in R. odorata) in ‘Dr. Huey’, R. ×fortuniana, and R. multiflora. Leaf net photosynthetic rate (Pn), transpiration rate (E) and stomatal conductance (gs) of all rootstocks decreased rapidly during the dry-down as substrate moisture content decreased from 25%. In ‘Dr. Huey’ and R. ×fortuniana, Pn, E, and gs were closely correlated with leaf RWC, while E and gs of R. odorata were not. Correlations between gas exchange rates (Pn, E, and gs) and leaf RWC in R. multiflora were weaker than those in ‘Dr. Huey’ and R. ×fortuniana. At low substrate moisture content (below 15%), Pn, E, and gs in R. odorata were lower than those in other rootstocks. Growth reduction was greatest in R. odorata, regardless of the least water deficit of the substrate, followed by R. multiflora and ‘Dr. Huey’. The results of this study suggest that R. ×fortuniana was the most tolerant and R. odorata was the least tolerant to drought stress.
Youping Sun, Genhua Niu, and Christina Perez
Salt tolerance of seven Texas Superstar® perennials [Malvaviscus arboreus var. drummondii (Turk’s cap), Phlox paniculata ‘John Fanick’ (‘John Fanick’ phlox), Phlox paniculata ‘Texas Pink’ (‘Texas Pink’ phlox), Ruellia brittoniana ‘Katie Blue’ (‘Katie Blue’ ruellia), Salvia farinacea ‘Henry Duelberg’ (‘Henry Duelberg’ salvia), Salvia leucantha (mexican bush sage), and Verbena ×hybrida ‘Blue Princess’ (‘Blue Princess’ verbena)] was evaluated in a greenhouse experiment. Plants were irrigated with a nutrient solution at electrical conductivity (EC) of 1.1 dS·m−1 (control) or a salt solution at EC of 5.0 or 10.0 dS·m−1 (EC 5 or EC 10) for 8 weeks. ‘John Fanick’ and ‘Texas Pink’ phlox plants in EC 5 had severe salt foliage damage, while those in EC 10 were died. Mexican bush sage in EC 10 had severe salt foliage damage. Turk’s cap, ‘Katie Blue’ ruellia, ‘Henry Duelberg’ salvia, and ‘Blue Princess’ verbena had minor foliar damage regardless of treatment. EC 5 reduced the shoot dry weight (DW) by 45% in ‘Texas Pink’ phlox and 11% to 18% in ‘Katie Blue’ ruellia, ‘Henry Duelberg’ salvia, and mexican bush sage, but did not impact the shoot DW of Turk’s cap and ‘John Fanick’ phlox. EC 10 further decreased the shoot DW of ‘Katie Blue’ ruellia, ‘Henry Duelberg’ salvia, and mexican bush sage plants by 32%, 29%, and 56%, respectively. EC 5 decreased leaf net photosynthesis (Pn) of ‘Texas Pink’ phlox and mexican bush sage, while EC 10 reduced Pn of all species except ‘Henry Duelberg’ salvia and ‘Blue Princess’ verbena. ‘Katie Blue’ ruellia and ‘Blue Princess’ verbena had relatively lower leaf Na concentration and ‘John Fanick’ phlox, ‘Texas Pink’phlox, and mexican bush sage had higher leaf Cl concentrations. In summary, Turk’s cap, ‘Katie Blue’ ruellia, ‘Henry Duelberg’ salvia, and ‘Blue Princess’ verbena were the most tolerant perennials, and ‘John Fanick’ phlox, ‘Texas Pink’ phlox, and mexican bush sage were the least tolerant to salinity.
Youping Sun, Joseph Masabni, and Genhua Niu
Excessive salinity in soil and irrigation water in combination with waterlogging in coastal regions can significantly reduce the productivity of many agricultural crops. To evaluate the plant growth responses to simulated seawater (SSW) flooding, seedlings of 10 vegetables (broccoli, chinese cabbage, chinese greens, cucumber, eggplant, kale, radish, ‘Red Crunchy’ radish, spinach, and tomato) were flooded with SSW at electrical conductivity (EC) of 44.0 ± 1.3 dS·m−1 or tap water at EC of 0.8 ± 0.1 dS·m−1 for 24 hours and grown subsequently for 2 weeks in a greenhouse. Chinese greens and cucumber plants died shortly after flooding with SSW, whereas other vegetables exhibited various degrees of visible salt damage. Chinese cabbage suffered the strongest reduction, whereas spinach, tomato, and eggplant exhibited the least decrease in dry weight (DW) due to SSW flooding in comparison with their perspective control. Two weeks after flooding treatment with SSW, net photosynthetic rate of broccoli, kale, spinach, and tomato was reduced by 43% to 67%, transpiration rate by 35% to 66%, and stomatal conductance (g S) by 51% to 82%. In summary, spinach, eggplant, and tomato were the most tolerant, whereas chinese cabbage, chinese greens, and cucumber were the least tolerant to SSW flooding.