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Tolerance to alkalinity was evaluated in Rose `Pink Cupido', Vinca `Apricot Delight', Chrysanthemum `Miramar', and Hibiscus `Bimini Breeze' and `Mango Breeze'. Plants were potted in a sphagnum peat moss-based growing medium and irrigated with water containing 0, 2.5, 5, 7.5 and 10 mm of Na bicarbonate. In rose, shoot mass was significantly decreased and chlorosis increased at the 5 mm treatment, indicating that the alkalinity toxicity is between 2.5 and 5 mm. In chrysanthemum, the concentration of Na bicarbonate did not significantly affect shoot mass, but caused a significant increase in leaf chlorosis at 5 mm or higher Na bicarbonate. This indicates an alkalinity toxicity level between 2.5 and 5 mm. In Vinca, shoot dry mass was not affected significantly, but leaf chlorosis was significantly increased with 5 mm of Na bicarbonate. This indicates an alkalinity toxicity level between 2.5 and 5 mm. In hibiscus `Mango Breeze', shoot mass was significantly increased at 2.5 and 5 mm, but was significantly decreased at 7.5 mm and above. Leaf chlorosis was significantly increased with a concentration of 5 mm and above, indicating that in hibiscus `Mango Breeze' the alkalinity toxicity level is between 5 to 7.5 mm. In hibiscus `Bimini Breeze', shoot mass was not significantly reduced, but leaf chlorosis exhibited a significant decrease at 7.5 mm. this indicates that in hibiscus `Bimini Breeze' the alkalinity toxicity level is between 7.5 and 10 mm. Growing medium pH increased with increasing levels of Na bicarbonate. The species showed varying capacity for acidification of the growing medium. All species, except rose and vinca, neutralized the alkalinity effect of 2.5 mm, but none of the species neutralized the effect of 5 mm and higher Na bicarbonate.

Mixture experiments were used to study the effect of Rb, K, and Na in combination with a number of bicarbonate concentrations on bean plants grown in hydroponics in a controlled environmental chamber. The objective was to separate the cation effect from the bicarbonate effect. The first experiment was a 3-component mixture-amount experiment using various ratios of Rb, K, and Na at 0 and 7.5 mm of bicarbonate. In the 0 mm bicarbonate control, the pure blends were ranked: Rb > Na > K for their effect on reducing shoot dry mass. The high toxicity to the Rb ion was probably due to direct Rb toxicity in addition to any general salinity effect. At 7.5 mm bicarbonate, shoot dry mass was decreased with all the counter-ions compared to the 0 mm bicarbonate control, and their toxicity was ranked: Rb > Na ≈ K. The next series of experiments were 2-component mixture-amount experiments at various ratios of K and Na at 2.5, 5 and 7.5 mm bicarbonate. In the 0 mm bicarbonate control, shoot dry mass decreased with increasing proportions of Na, indicating a specific Na toxicity. The same trend was observed at 2.5 mm bicarbonate. In the 7.5 mm bicarbonate treatment, both Na and K were equally toxic. At low concentration of bicarbonate, the Na is more toxic than the bicarbonate. At higher concentrations of bicarbonate, both Na and bicarbonate exhibit similar levels of toxicity.

The effect of Rb⁺ and Na⁺ as counter-cations of HCO₃ ⁻ was evaluated on bean (Phaseolus vulgaris L. cv. Poncho) plants using mixture experiment statistical methodology in a series of experiments set up in a controlled environment chamber. Mixture experiments using three components (Rb⁺, K⁺, and Na⁺) or two components (K⁺ and Na⁺) were conducted to delineate the toxicity of HCO₃ ⁻ versus the counter-cation effect. The quantitative separation of the toxic effects was possible only when the individual stress had an additive effect when combined with the other stress. Potassium mixtures were used as reference for comparison with other mixtures because plants did not respond to K⁺, probably because it was included at a minimum concentration of 2.5 mm K⁺ or because it was supplied in the preestablishing solution. Rubidium caused a decrease in shoot dry weight (SDW), but SDW accumulation was even lower when HCO₃ ⁻ was added to the Rb⁺ solutions. However, Rb⁺ was not included in follow-up experiments because the response of plants to Rb⁺ was very similar to that of Na⁺. The toxic effect of Na⁺ caused SDW to decrease at a rate of 3.7% per millimolar increase of Na⁺. However, the effect of HCO₃ ⁻ was dependent on its concentration, because at 2.5 mm HCO₃ ⁻, the decrease in SDW was 12.7% per millimolar HCO₃ ⁻, whereas at 3.75, 5, and 5.65 mm, the decrease was 11.0%, 7.8%, and 10.7% per millimolar HCO₃ ⁻, respectively. At 7.5 mm HCO₃ ⁻, the decrease in SDW was 4.2% to 8.2% per millimolar increase in HCO₃ ⁻, respectively. The decreasing HCO₃ ⁻ rate may be explained by the nonadditive effect between HCO₃ ⁻ and Na⁺ at high alkalinity levels.

Marigolds are one of the most popular annual ornamental plants; both, the short-stature cultivars (Tagetes patula L.) and the taller cultivars (T. erecta L.) are used as container plants in landscape and garden settings. Tagetes erecta varieties can also make excellent cut and dried flowers for the florists' market. The present study was conducted to evaluate the response of T. patula ‘French Vanilla’ and T. erecta ‘Flagstaff’ and ‘Yellow Climax’ to irrigation with saline water with and without pH control. Marigold plugs were transplanted into greenhouse sand tanks and established for 1 week under nonsaline conditions. Ten treatments were then applied with electrical conductivities of irrigation water (EC_w) of 2, 4, 6, 8, and 10 dS·m⁻¹ and pH levels of 6.4 and 7.8. Growth of all three cultivars decreased in response to irrigation with saline waters at pH 6.4. Compared with the nonsaline controls, ‘French Vanilla’ exhibited a 20% to 25% decrease in plant height, leaf dry weight (DW), and shoot DW when irrigated with 4 dS·m⁻¹ water. However, the number of flowering shoots and the diameter and number of flowers were not significantly affected until the EC_w exceeded 8 dS·m⁻¹. Growth of ‘Flagstaff’ and ‘Yellow Climax’ also decreased as EC_w increased. Shoot DW of the tall cultivars decreased by 30% and 24%, respectively, in response to the 4 dS·m⁻¹ treatment, but additional salt stress had no further effect on DW production. Marigolds were highly sensitive to high pH. Plants irrigated with nonsaline water with pH at 7.8 exhibited a 50%, 89%, and 84% reduction in shoot DW in ‘French Vanilla’, ‘Flagstaff’, and ‘Yellow Climax’, respectively, compared with plants irrigated with water with pH 6.4. Marigold cultivars were rated as moderately tolerant to salinity because growth was affected when water EC_w exceeded 8 dS·m⁻¹. Salinity tended to reduce internode elongation, resulting in attractive plants. Compactness was not increased as a result of a decrease in DW, resulting in attractive plants, which show great promise as bedding or landscape plants in salt-affected sites provided that the pH of the soil solutions remains acidic. Under our experimental conditions in the sand tank system, the EC_w was essentially equivalent to those of the sand soil solution; however, considering that the EC of the sand soil solution is ≈2.2 times the EC of the saturated soil extract (EC_e), our salinity treatments may be estimated as 0.91, 1.82. 2.73, 3.64, and 4.55 dS·m⁻¹. Thus, the threshold EC_w at which marigold cultivars exhibited acceptable growth, 8 dS·m⁻¹, would be equivalent to EC_e of 3.64 dS·m⁻¹.

Scarcity of good-quality water for landscape irrigation is a major concern in arid and semiarid regions as a result of the competition with the urban population. Competing claims from urban, agricultural, environmental, and industrial groups leaves less water or water of lower quality for use in landscape maintenance. Although degraded waters, high in both salinity and alkaline pH, may challenge plant establishment and growth, these waters must be considered as valuable alternatives to the use of fresh water resources for landscape sites. The objective of the present study was to determine the effect of irrigation with saline water, with and without pH control, on the mineral ion relations of three marigold cultivars: Flagstaff, Yellow Climax, and French Vanilla. Treatments were five electrical conductivities of irrigation water (EC_w): 2, 4, 6, 8, and 10 dS·m⁻¹, and two pH levels: 6.4 and 7.8. Plants of ‘French Vanilla’ and flowering stems of ‘Flagstaff’ and ‘Yellow Climax’ were harvested at flower maturity. Leaves of the taller cultivars, Flagstaff and Yellow Climax, were collected separately from the main axis and from the lateral stems, whereas in ‘French Vanilla’, leaves were combined. Total sulfur, total phosphorus, Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl⁻, Fe²⁺, Zn²⁺, Cu²⁺, and Mn²⁺ concentrations in leaf and stem tissues were determined. The three marigold cultivars were strong Ca²⁺-accumulators and this response was more evident at the lower pH level. However, leaf Ca²⁺ tended to decrease as salinity increased despite a threefold increase in substrate Ca²⁺. Leaf Mg²⁺ increased as salinity increased and main stem leaves of the taller cultivars accumulated more Mg²⁺ than leaves on the lateral branches. The reverse was true for leaf K⁺; leaves on the lateral branches were stronger K⁺-accumulators than those on the main stem. Potassium concentrations in leaves of marigold irrigated with waters at pH 6.4 tended to decrease as EC_w increased. Marigold seems to possess an efficient Na⁺ exclusion mechanism, which restricts Na⁺ accumulation in the leaves. Patterns of total phosphorus accumulation in leaf tissues were not consistent over the range of EC_w treatments. Among the micronutrients, Fe²⁺ and Mn²⁺ tended to be partitioned to the younger rather than the older leaves. The decrease in marigold growth was associated with nutrient ion imbalance as demonstrated by the reduction in K⁺ concentration and the increase in Mg²⁺ and Cl⁻ in leaf tissue. Despite the reduction in growth, the aesthetic value of the cultivars was not detrimentally affected by application of saline waters with EC_w values as high as 8 dS·m⁻¹.

Ranunculus, grown as a field crop in southern and central coastal California, is highly valued in the cut flower and tuberous root markets. However, concerns regarding the sustainability of ranunculus cultivation have arisen when the plantations are irrigated with waters of marginal quality because the viability of the tuberous roots may be compromised. A study was initiated to evaluate the effect of saline irrigation waters, with and without pH control, on the growth of plants and tuberous roots of ranunculus. Treatments consisted of four irrigation water solutions with increasing concentration of Ca²⁺, Mg²⁺, Na⁺, SO₄ ²⁻, and Cl⁻ to meet an electrical conductivity (EC) of 2, 3, 4, and 6 dS·m⁻¹ and pH 6.4. The 3, 4, and 6 dS·m⁻¹ solutions were replicated with uncontrolled pH, which averaged 7.8 over the trial. Ranunculus ‘Yellow ASD’ and ‘Pink CTD’ seedlings were transplanted into greenhouse sand tanks and irrigated twice daily with treatment solutions. Shoot dry weight of plants irrigated with 2 dS·m⁻¹ solutions was 7.20 g and 6.66 g in ‘Yellow ASD’ and ‘Pink CTD’, respectively; however, increasing EC from 2 to 3 dS·m⁻¹ induced an 83% and 78% decrease, respectively. Tuberous root fresh weight of control plants, 7.45 g and 8.42 g for ‘Yellow ASD’ and ‘Pink CDT’, respectively, was decreased by 82% and 89% when EC was 6 dS·m⁻¹. High pH of irrigation water caused an additional decrease in shoot dry weight and tuberous root weight. In control plants, 83% and 76% of tuberous roots of ‘Yellow ASD’ and ‘Pink CTD’, respectively, that were transplanted in the following season produced new shoots; however, tuberous roots sprouting percentage from plants irrigated with EC 4 dS·m⁻¹ water decreased to 42.9% and 58.3% and to 11.1% and 45.0% with EC 6 dS·m⁻¹. The hypersensitivity of ranunculus to salinity was associated with a significant decrease in Ca²⁺ and K⁺ tissue concentration. In ‘Yellow ASD’, Ca²⁺ decreased from 202 mmol·kg⁻¹ in control plants to 130 mmol·kg⁻¹ in plants irrigated with 3 dS·m⁻¹ solutions and pH 6.4. In ‘Pink CTD’, the decrease was from 198 mmol·kg⁻¹ to 166 mmol·kg⁻¹. Potassium was similarly affected. Compared with control plants (405 mmol·kg⁻¹), shoot Na⁺ concentration was increased by 101% in ‘Yellow ASD’ and by 125% in ‘Pink CTD’ when irrigated with 6 dS·m⁻¹ water. Salt sensitivity of ranunculus, as determined by growth of the flowering stems and viability of the tuberous roots, was increased by irrigation with alkaline waters, which was associated with additional increases in Na⁺ and Cl^– tissue concentration and decreased iron accumulation. Hypersensitivity to salinity makes ranunculus crop a poor candidate for water reuse systems; however, further research is warranted to elucidate the possibility of enhancing its tolerance to salinity by supplemental Ca²⁺ and K⁺ and acidification of irrigation water.

Sustainable horticultural production will increasingly have to rely on economically feasible and environmentally sound solutions to problems associated with high levels of bicarbonate (HCO ^- ₃) and associated high pH in irrigation water. The ability of arbuscular mycorrhizal fungi (AMF; GlomusZAC-19) to enhance plant tolerance to HCO₃ ^- was tested on the growth, physiology and nutrient uptake of Rosamultiflora Thunb. ex J. Murr. cv. Burr (rose). Arbuscular mycorrhizal colonized and noninoculated (non-AMF) plants were treated with 0, 2.5, 5, and 10 mm HCO ^- ₃. Increasing HCO ^- ₃ concentration and associated high pH and electrical conductivity (EC) reduced plant growth, leaf elemental uptake and acid phosphatase activity (ACP), while increasing alkaline phosphatase activity (ALP). Inoculation with AMF enhanced plant tolerance to HCO ^- ₃ as indicated by greater plant growth, leaf elemental uptake (N, P, K, Ca, Fe, Zn, Al, Bo), leaf chlorophyll content, higher mycorrhizal inoculation effect (MIE), lower root iron reductase activity, and generally lower wall-bound ACP (at 2.5 mm HCO₃ ^-), and higher soluble ALP (at 10 mm HCO₃ ^-). While AMF colonization (arbuscules, vesicles, and hyphae formation) was reduced by increasing HCO ^- ₃ concentration, colonization still occurred at high HCO ^- ₃. At 2.5 mm HCO₃ ^-, AMF plant growth was comparable to plants at 0 mm HCO₃ ^-, further indicating the beneficial effect of AMF for alleviation of HCO₃ ^- stress.

The present study was conducted to determine the critical optimum and toxic concentrations of potassium (K) using segmented analysis and its relationship with some physiological, anatomical, and nutritional responses to increasing K in hydroponically grown Lilium sp. L. cv. Arcachon. Plants were fertigated with nutrient solutions containing K (K_ext) at 0, 2.5, 5.0, 7.5, 12.5, 17.5, 22.5, and 30 mmol·L⁻¹. Maximum flower diameter occurred when, on a dry mass basis, shoot K (K_int) ranged from 504 to 892 mmol·kg⁻¹; however, a lower K_int was required to obtain maximum biomass accumulation and shoot length (384 and 303 mmol·kg⁻¹, respectively). Potassium increased in all plant organs as K in the nutrient solution increased. Nitrogen increased in young leaves and magnesium (Mg) decreased as K_ext increased. Concentrations of K_ext from 5 to 17.5 mmol·L⁻¹ increased the size of chlorenchyma and occlusive cells; however, metaxylem vessels were unaffected. Net photosynthetic rate was higher in young leaves, whereas water potential increased in both young and mature leaves when K_ext was greater than 22.5 mmol·L⁻¹. Critical concentrations varied according to the growth parameter. Optimum K_int ranged from 303 to 384 mmol·kg⁻¹ for vegetative parts, whereas parameters related with flower growth ranged from 427 to 504 mmol·kg⁻¹. Concentration of 504 mmol·kg⁻¹ K_int was associated with optimum growth for all the parameters assessed, whereas a K_int greater than 864 mmol·kg⁻¹ was associated with a decline in growth; thus, these concentrations were considered as the critical optimum and critical toxicity levels, respectively. The optimum and toxicity critical K_int were estimated when K_ext in the nutrient solutions was 5.6 and 13.6 mmol·L⁻¹, respectively.

Planting depth during container production may influence plant growth, establishment, and subsequent landscape value. A lack of knowledge about the effects of common transplanting practices may lead to suboptimal performance of planted landscape trees. Planting depth, i.e., location of the root collar relative to soil grade, is of particular concern for posttransplant tree growth both when transplanted to larger containers during production and after transplanting into the landscape. It is unknown whether negative effects of poor planting practices are compounded during the production phases and affect subsequent landscape establishment. This study investigated effects of planting depth during two successive phases of container production (10.8 L and 36.6 L) and eventual landscape establishment using lacebark elm (Ulmus parvifolia Jacq.). Tree growth was greater when planted at grade during the initial container (10.8 L) production phase and was reduced when planted 5 cm below grade. In the second container production phase (36.6 L), trees planted above grade had reduced growth compared with trees planted at grade or below grade. For landscape establishment, transplanting at grade to slightly below or above grade produced trees with greater height on average when compared with planting below grade or substantially above grade, whereas there was no effect on trunk diameter. Correlations between initial growth and final growth in the field suggested that substantial deviations of the original root to shoot transition from at-grade planting was more of a factor in initial establishment of lacebark elm than the up-canning practices associated with planting depth during container production.

Landscape irrigation is the second largest user of reclaimed water in industrialized countries; however, its high concentration of soluble salts, especially Na⁺ and Cl^–, may induce growth reduction and leaf necrosis or bronzing in ornamental species. The present study was conducted to determine the growth and quality responses and nutritional ion imbalances of selected landscape species during the container production phase when subjected to irrigation with water of increasing NaCl + CaCl₂ concentrations. Plants of boxwood [Buxus microphylla var. japonica (Mull. Arg. ex Miq) Rehder & E.H. Wilson], escallonia (Escallonia ×exoniensis hort. Veich ex Bean), hawthorn [Raphiolepis indica (L.) Lind. Ex Ker Gawl. × ‘Montic’], hibiscus (Hibiscus rosa-sinensis L.), and juniper (Juniperus chinensis L.) were grown in a greenhouse in the Spring–Summer and in the Fall–Winter in separate experiments. Saline irrigation consisted of solutions with electrical conductivities (EC_iw) of 0.6, 2, 4, 6, and 8 dS·m⁻¹ in the Spring–Summer experiment and 0.6, 4, 6, 8, and 12 dS·m⁻¹ in the Fall–Winter. Growth of the five species decreased when irrigated with saline waters. Leaf growth was highly sensitive to salinity and the average decrease in leaf dry weight was the criterion used to rank the tolerance of the species. In the Spring–Summer experiment, the ranking was (higher tolerance to lower tolerance): juniper ∼ boxwood > escallonia > hawthorn > hibiscus, whereas in Fall–Winter, the ranking was: juniper ∼ boxwood > hibiscus > escallonia > hawthorn. The species were ranked according to their visual attractiveness in the Spring–Summer experiment. The threshold EC_iw at which visual attractiveness was affected gave the following ranking (higher to lower tolerance): hibiscus > juniper > escallonia > hawthorn > boxwood. Estimating the EC of drainage water from threshold EC_iw, boxwood was classified as sensitive, hawthorn as moderately sensitive, escallonia as moderately tolerant, and hibiscus and juniper as highly tolerant. Tolerance of juniper was ascribed to Na⁺ and Cl^– retention in the roots observed in both growing seasons and to the higher root biomass that allowed a higher accumulation of salts in this organ, preventing translocation to the leaves. Although boxwood exhibited acceptable tolerance in terms of growth, visual quality severely decreased; in contrast, growth of hibiscus was the most severely reduced but was rated as the most tolerant species in terms of visual quality. This opposite response may be the result of an excellent capacity to compartmentalize salts in hibiscus, whereas in boxwood, this mechanism may be absent.