Search Results

You are looking at 11 - 20 of 27 items for

  • Author or Editor: Raul I. Cabrera x
Clear All Modify Search

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.

Free access

Containerized crape myrtle (Lagerstroemia indica L. × Lagerstroemia fauriei Koehne `Tonto') plants were grown for 9 months under various nitrogen fertility regimes, and then transplanted to a sandy loam soil with minimal management to evaluate their landscape establishment and growth performance. During the nursery phase plants were irrigated, except over an overwintering period, with complete nutrient solutions differing in applied N concentration, ranging from 15 to 300 mg·L-1. By 16 weeks after transplanting (WAT) into the landscape soil, plant biomass was significantly higher in the plants that had been grown with higher N supplies and had been among the smallest at transplant. Such plant growth response was linearly and positively correlated to plant N status at transplant. Plant shoot to root ratio and tissue N, Ca, S, and Fe concentrations, which had been significantly affected by the N fertilization regime in the nursery, equalized over time after transplant, with no significant differences observed among treatments by 16 WAT. Flowering response in the landscape was delayed in plants originally grown with the higher N supplies. Plant survival and establishment per se were not affected by treatments; no plants were lost, and aside from the differences in size and flower timing, all plants were considered aesthetically similar.

Free access

Greenhouse rose plants, `Bull's Eye', budded on the rootstocks Rosa manetti and R. × `Natal Briar', were grown in containers filled with a peat-based growing medium. The plants were irrigated with a 0.5× Hoagland solution salinized with a fixed 12-mM Na solution made up of seven ratios of NaCl, Na2SO4, and NaNO3 (100:0, 50:50:0, 0:100:0, 0:50:50, 0:0:100, 50:0:50, and 33:33:33). The results after four flushes of growth and flowering showed higher dry weight productivities in R. manetti plants. Salt composition (i.e., counter-anion ratios) significantly affected the dry weight yield of `Natal Briar' plants, with those irrigated with 100% Na2SO4 and NaNO3 having the highest and lowest values, respectively. While the plants budded on R. manetti did not show significant responses to salt composition, there was a strong tendency for higher dry weight yields in binary salt (anion) compositions. Leachates collected throughout the study showed similar pH (7.5) and electrical conductivities (4.7 dS/m) for all salt treatments. Leachate Cl- concentrations were linearly correlated with Cl- application, whereas leachate Na+ concentrations remained similar among treatments. Plants on R. manetti accumulated less leaf Na+ and Cl- than in R. × `Natal Briar' plants, with lower values observed, in general, in plants irrigated with solutions containing Na2SO4.

Free access

In this preliminary study, we evaluated the salinity tolerance of selected herbaceous perennials. Liners of Rudbeckia hirta `Becky Orange', Phlox paniculata `John Fanick', Coreopsis grandiflora `Early Sunrise', Lantana ×hybrida `New Gold' and Cuphea hyssopifolia `Allyson' were transplanted to 4-gal plastic containers filled with peat moss: pine bark: sand (3:1:1) medium amended with dolomite, Micromax and Osmocote 18-6-12 (at 2, 0.6, and 6 kg·m3, respectively). The plants were irrigated for 14 weeks with tap water containing 0, 1.5, 3, 6, 12, and 24 mM of NaCl: CaCl2 salt mixture (2:1 molar ratio). Increasing salt stress had differential effects on plant growth and quality, with Rudbeckia and Phlox being the most adversely affected even by the lowest salt treatment of 1.5 mM, with dry weight reductions of ∼25% compared to the controls. Conversely, Lantana and Cuphea tolerated extremely well salinity up to 12 mM, where dry weight reductions were less than 10% of the nonsalinized controls. The Lantana and Cuphea plants also presented the lowest leaf Cl accumulation with increasing salinity, whereas Coreopsis showed the highest Cl accumulations at any salinity level. Plots of leaf Cl concentration against dry weights showed steeply declining relationships for Rudbeckia and Phlox plants, confirming our observations and assessment that these species are to be considered salt-sensitive. Leaf Na accumulation is currently being analyzed.

Free access

N deprivation is known to increase the rate of N uptake by graminaceous plants, but such response has not been reported for mature woody plants. A recirculating nutrient solution system was utilized to study the effect of intermittent N-deprivation on N uptake by mature `Royalty' rose plants. Plants received a nutrient solution lacking N for 4, 8 or 16 days, after which one containing N was supplied for 4 days. N-deprivation resulted in a 2-3 fold increase in N uptake rate compared to control plants supplied continuously with N (e.g., 143 vs 62 mg N plant-1 day-t). The magnitude of this deprivation-enhanced N uptake was not affected by either the duration of N-deprivation or the plant developmental stage.

A characteristic diurnal pattern of N uptake was observed in both N-starved and control plants. Uptake oscillated between minimum rates in the morning and maximum rates in the evening, the latter occurring 4-6 hr after the maximum transpiration rates.

The ability to increase the rate of N uptake in roses by depriving them of N for several days may be of practical importance for increasing N fertilizer use efficiency and decreasing N losses to leaching.

Free access

N uptake by greenhouse roses is out of phase with flower shoot elongation, such that N uptake is highest when shoots are not growing and lowest when shoots are elongating rapidly. Isotopically labelled 15N fertilizer was supplied at different stages of one flowering cycle to `Royalty' rose plants growing in a static nutrient solution system to study the partitioning of recently-absorbed N and the dynamics of N partitioning. After a two-day exposure, whole plants were harvested, separated into old and new leaves, stems, and roots, and analyzed for total N and 15N enrichment. During rapid shoot elongation, N uptake by roots supplied 16 to 36% of shoot N demand. The remaining N came from other organs, particularly old stems and leaves. The increased N uptake later in the flowering cycle was sufficient to meet shoot N demand and replenish the N supply in old foliage and woody tissues. These organs continued to accumulate N until the subsequent bud break, when this N became available for the next cycle of flowering shoot growth.

Free access

Nitrogen leaching losses of 21, 40 and 49% were measured from container-grown `Royalty' roses irrigated for one year with nutrient solutions containing 77, 154 and 231 mg N/l. There were no significant differences in number of flowers per plant or dry matter per plant. The N present in the harvested flowers accounted for 43, 27 and 17% of the N applied for the 77, 154 and 231 mg N/l treatments, respectively.

Plants receiving 154 mg N/l at leaching fractions of 0.1, 0.25 and 0.5 had corresponding N leaching losses of 22, 38 and 56%. In this experiment, however, the 0.5 leaching fraction produced yields significantly higher than those of the 0.1 and 0.25 treatments. The N recovered in the harvested flowers accounted for 28, 25 and 19% of that applied to the 0.1, 0.25 and 0.5 treatments, respectively.

The results of these studies suggest that modifications in current irrigation and fertilization practices of greenhouse roses would result in a considerable reduction of N leaching losses and enhance N fertilizer use efficiency, without loss of cut flower yield and quality.

Free access

Greenhouse rose (Rosa × spp. L.) production is facing the use of poor-quality irrigation waters and regulatory pressures to recycle runoff and drainage effluents. Two experiments (were conducted to evaluate the yield and quality and ion accumulation responses of roses grafted on various rootstocks to increasing salinity stress. In Expt. 1, the scion ‘Bridal White’ grafted on ‘Manetti’, R. odorata (Andr.), ‘Natal Briar’, and ‘Dr. Huey’ were irrigated over four flowering cycles with complete nutrient solutions supplemented with NaCl at 0, 5, and 30 mm. In Expt. 2, plants of ‘Red France’ on ‘Manetti’ and ‘Natal Briar’ were irrigated over six flowering cycles with complete nutrient solutions supplemented with NaCl + CaCl2 (2:1 m ratio) at 0, 1.5, 3, 6, 12, and 24 mm. Salt concentration increases significantly and negatively affected the biomass, cut flower production, and foliage quality of the roses in both experiments, but the responses were modulated by rootstock selection. ‘Manetti’ plants in general sustained better absolute and relative biomass and flower yields, accumulated less Na+ and Cl in its tissues, and showed less toxicity symptoms with increasing salinity than the others. ‘Natal Briar’ also had similar absolute productivity responses as ‘Manetti’ but were afflicted by a significantly different mineral nutrient profile, including higher accumulations and toxicities with Na+ and Cl that led to lower foliage visual ratings. Conversely, the relative yields of plants on ‘Dr. Huey’ and R. odorata were similarly reduced by increasing salinity, but the former had lower Na+ and Cl concentrations in its tissues and better visual scores than the latter, which fared as the worst. A combined analysis of the results suggests that on a productivity basis (biomass and flower yields), greenhouse roses could withstand overall maximum electrical conductivities (i.e., osmotic effects) of applied fertigation solutions of 3.0 ± 0.5 dS·m−1. On the other hand, and considering the aesthetic responses (visual scores) of on-plant and harvested foliage (cut flower shoots), greenhouse rose tolerance to applied Na+ and Cl concentrations (ion-specific effects) could range up to 10 ± 2 mm.

Free access

Field (choice) and laboratory (no choice) studies were conducted to evaluate the susceptibility of 12 crape myrtle (Lagerstroemia) cultivars, representing two species and their interspecific hybrids, to feeding damage by the flea beetle (Altica litigata Fall). The results indicate that as a group, the L. indica L. cultivars were more susceptible to attack and significant herbivory damage by Altica beetles, whereas all the L. fauriei Koehne cultivars and most of the interspecific L. indica × fauriei hybrids were resistant. Significant differences in feeding damage were observed between the new and older leaves in the susceptible hybrid ‘Biloxi’ and L. indica ‘Whit IV’, but not in the rest of the cultivars. Mineral nutrient content differences were observed between species with L. indica cultivars having a significantly contrasting nutrient status profile compared with the L. fauriei and interspecific hybrid cultivar groups. The results indicate that the factors influencing Altica flea beetle-feeding preferences and damage are inherited and therefore will allow the implementation of pest management practices that minimize damage and optimize chemical control strategies. In addition, opportunities may exist for breeding and selection efforts that could lead to superior cultivars with insect resistance.

Free access

Scarcity and competition for good quality and potable water resources are limiting their use for urban landscape irrigation, with several nontraditional sources being potentially available for these activities. Some of these alternative sources include rainwater, stormwater, brackish aquifer water, municipal reclaimed water (MRW), air-conditioning (A/C) condensates, and residential graywater. Knowledge on their inherent chemical profile and properties, and associated regional and temporal variability, is needed to assess their irrigation quality and potential short- and long-term effects on landscape plants and soils and to implement best management practices that successfully deal with their quality issues. The primary challenges with the use of these sources are largely associated with high concentrations of total salts and undesirable specific ions [sodium (Na), chloride (Cl), boron (B), and bicarbonate (HCO3 ) alkalinity]. Although the impact of these alternative water sources has been largely devoted to human health, plant growth and aesthetic quality, and soil physicochemical properties, there is emergent interest in evaluating their effects on soil biological properties and in natural ecosystems neighboring the urban areas where they are applied.

Full access