Water loss of Nerium oleander growing in two soil types was determined from mid-June through mid-October. Plants (1 year old, 3.8 liter) were obtained from a local nursery and transplanted in May into 18.9-liter Iysimeter pots containing either clay loam or bluepoint sand. Controls were lysimeter pots containing each soil type but without plants. Irrigation was applied at two rates, approximately field (pot) capacity and 50% of that amount. Irrigation frequency was determined by visual inspection of the plants and was held constant for both irrigation rates in a given soil type. Frequency ranged from 2 to 3 days for the sand and 2 to 5 days for the clay loam. Water loss was determined every 24 h. Plant water loss was higher at the higher irrigation rate. Decreasing irrigation rate by 50% resulted in a 20% to 40% reduction in plant water use in clay loam and a 15% to 30% reduction in sand without affecting plant quality. Plant water loss in the sandy soil was ≈50% greater than in clay loam 48 h after irrigation. Implications of these findings in developing an optimum irrigation model for landscape plants will be considered.
The effect of irrigation management strategies on the quality and storage performance of `O'Henry' peaches [Prunus persica (L.) Batsch] was studied for two seasons. The deficit irrigation treatment induced a higher fruit soluble solids concentration and lower fruit weight. The excess irrigation treatment, compared to the optimum treatment, increased the rate of fruit water loss without altering fruit quality and storage performance. Scanning electron microscope observations indicated a higher density of trichomes on fruit from the deficit and optimum irrigation treatments than from the excess irrigation treatment. Light microscopy studies indicated that fruit from deficit and optimum irrigation had a continuous and much thicker cuticle than fruit from the excess irrigation treatment. These differences in exodermis structure may explain the high percentage of water loss from fruit from the excess irrigation treatment compared to the deficit and optimum irrigation treatments.
A foliar application of 5 × 10−5 M phenylmercuric acetate plus a wetting agent reduced water loss by transpiration from chrysanthemum plants by more than 30% for a period of 4 days following treatment without causing tissue damage or inhibiting growth and flowering. This reduction of transpiration was associated with a reduction of stomatal pore size. However, treatment concentration was critical, as foliar damage and reduction in growth occurred at high concentrations of PMA.
Several film forming antitranspirants were applied to salable, flowering chrysanthemum plants prior to placement in a controlled environment devised to simulate the interior of a home. Significant reductions in water loss resulted with all applications, with over a 40% reduction at highest concentrations. No discernable increase in floral display life was observed with any treatment. Higher concentrations of chemicals caused yellowing of foliage, and in some cases imparted a sticky residue or in some way impeded normal floral expansion. Film effectiveness persisted for at least 2 weeks with consistantly high transpiration losses for non-treated plants.
Zein is an alcohol-soluble protein isolated from corn. The effect of ground cover films prepared from zein on the growth of tomato plants and corresponding evaporative water loss was investigated in greenhouse experiments. Results indicated that there was a decrease in water loss from the growth media for pots treated with zein films compared to the control (no film). There was an 11% increase height and 65% increase in dry weight of the treated plants relative to the control. In a second experiment, tomato plants mulched with zein isolates, low in free fatty acids (LFFA), exhibited an 18% increase in height and a 28% increase in dry weight compared to the control. Tomato plants treated with black polyethylene sheathing mulch were the tallest of the plants tested and had the greatest dry weight. Adding corn gluten meal directly to the soil surface resulted in tomato plants that were 26% taller and 29% heavier than those grown in untreated soil. Zein isolate films appear to be a viable ground cover replacement for polyethylene sheathing.
A plantless system using subirrigation was developed to measure water absorption and loss in soilless media amended with hydrophilic polymers, a wetting agent, or combinations of these amendments. Peat-perlite-vermiculite and bark-peat-perlite controls achieved 67% and 52% of container capacity, respectively, after 20 daily irrigation cycles. Maximum water content of amended media was 78% of container capacity. Adding only a hydrophilic polymer did not increase total water content significantly. Adding a wetting agent increased water absorption in both media. However, when hydrophilic polymer and wetting agent were present, the medium absorbed more water than with wetting agent alone. More extractable water was removed from media containing wetting agent. Water loss rate by evaporation was not affected significantly by medium, hydrophilic polymer, wetting agent, or any combination of these variables.
Cuticular resistance to water loss was estimated for drought resistant and susceptible cowpea [vigna unguiculata (L.) Walp.] genotypes in a series of field and greenhouse experiments. The procedure consisted of harvesting the youngest, fully-expanded middle trifoliate leaf of a well-watered plant. The detached leaf was weighed immediately and then allowed to dry in an air-conditioned laboratory (about 25°C). Leaves again were weighed 24 and 48 hr after detachment and then oven dried at 70° for 24 hr. Oven dry weight was used to determine leaf water content (LWC) at each sampling time. Specific drought resistant and susceptible genotypes consistently expressed increased or reduced LWC, respectively, 48 hr after detachment. Interestingly, named cultivars generally had even higher LWC values after drying than did the selected resistant genotypes. Intraspecific variability for the trait appears to exist and may be related to drought adaptation in cowpea.
`Angelika White' poinsettias (Euphoria pulcherrima Willd.ex. Klotzch) were grown hydroponically with modified Hoagland's solution concentrations of 2 or 8 mS·cm-1. The 8-mS·cm–1 rate was imposed by proportionate increases in Ca(NO3)2, KNO3, and MgSO4. Water use, whole plant fresh mass, and pan evaporation were measured gravimetrically twice weekly over a 2-week period beginning 12 Oct. 1995. Poinsettia leaf water loss (g H2O/dm2 of estimated leaf area per day) was 0.30 and 0.22 times pan evaporation (g H2O/dm2 of pan area per day) for the plants in the 2 and 8 mS·cm–1 solutions, respectively (a 25% reduction in water loss for plants in the 8 mS·cm–1 solution), as compared to plants in the 2 mS·cm–1 solution. At initial anthesis, a reciprocal transfer of plants between the 2 and 8 mS·cm–1 solutions was used to investigate the time when plants were sensitive to high soluble salts for bract necrosis. Other plants were maintained throughout the experiment in the 2 and 8 mS·cm–1 solutions. On 15 Jan. 1996, plants were harvested and total lamina surface of leaves and bracts, number of necrotic bracts, and dry mass of leaves, bracts, stems, and roots were recorded. The results indicated that exposure to high soluble salts (8 mS·cm–1) prior to anthesis significantly increased the percent incidence of bract necrosis and decreased root growth. The smaller the root dry mass as a percent of total plant dry mass the greater the incidence of bract necrosis (Y = 0.0972X2 – 3.78X + 38.7, r 2 = 0.69).
Fruit of pepper (Capsicum annuum L.) is hollow by nature, which limits its water reservoir capacity, and as such, small amounts of water loss result in loss of freshness and firmness, which reduce fruit quality, shelf life, and market value. In order to understand the basis for water loss from fruit, 10 pepper accessions with wide variation in water loss rate were used to study physiological and biochemical factors associated with postharvest water loss in ripe pepper fruit during storage. Postharvest water loss rate in ripe pepper fruit stored at 20 °C, and 85% relative humidity, was found to be associated with cell membrane ion leakage, lipoxygenase activity, and total cuticular wax amount. Total cuticular wax amounts were highest in the high-water-loss pepper fruit, and lowest in the low-water-loss fruit. However, total cuticle amount (isolated enzymatically and quantified gravimetrically), total cutin monomer amount, and the amount of individual cutin monomer and wax constituents (determined using gas chromatography mass spectrometry) indicated no direct association with postharvest water loss rates. Fruit fresh weight, pericarp weight, pericarp surface area, pericarp thickness, initial water content, and dry matter were highly associated with each other, but less so with water loss rate. Fruit of accessions displaying high fruit water loss rate matured and ripened earlier than fruit of accessions displaying low-water-loss rate. Cell membrane ion leakage and lipoxygenase activity were higher after storage than immediately after harvest. Pepper fruit total cuticle wax amount, lipoxygenase activity, and cell membrane ion leakage were directly related to postharvest water loss rate in pepper fruit during storage.
Desiccation of containerized plants at retail outlets due to inadequate watering is a recurring problem. Water stress can decrease plant quality and survivability. Treatments that could reduce plant transpiration without lowering plant quality could be beneficial in maximizing the likelihood that plants would not become water stressed between waterings at retail outlets. Abscisic acid (ABA) is known to be involved in the regulation of stomatal aperatures, the major control mechanism for transpirational water loss. Containerized plants of four cultivars of hibiscus were thoroughly sprayed with S-ABA at concentrations of 0, 125, 250 or 500 mg·L–1. Plants were held under simulated retail conditions and were not watered until visible wilting occurred. Transpiration and pot weights were monitored over time. Transpiration rates and weight loss percentages were negatively correlated with S-ABA concentrations. Effects on transpiration rates lasted for at least 30 hours after treatment. For mean hours to wilt, there was interaction between S-ABA treatments and cultivars. For the most sensitive cultivar (`Double Apricot'), treatment with S-ABA at 500 mg·L–1 almost doubled the time to plant wilt (130 h) compared to the control treatment (72 hours). Hours to wilt was increased 24% for `Double Pink' treated at the highest rate. For `Double Red' and `Single Pink', hours to wilt was not affected by treatments. For some hibiscus, S-ABA treatments prior to placement of plants at retail outlets might decrease the chances that the plants would become severely water stressed.