Computer modeling was used to study the effect of container volume and shape on summer temperature patterns for black polyethylene nursery containers filled with a 4 pine bark: 1 sand (v/v) rooting medium and located in Phoenix, Ariz. (lat. 33.5°N, long. 112°W) or Lexington, Ky. (lat. 38.0°N, long. 84.4°W). For both locations, medium temperatures were highest at the east and west container walls, halfway down the container profile, regardless of container height (20 to 50 cm) or volume (10 to 70 liters). The daily maximum medium temperature (Tmax) at the center was lower and occurred later in the day as container volume was increased because of an increased distance to the container wall. For both locations, predicted temperature patterns in rooting medium adjacent to the container wall decreased as the wall tilt angle (TA) increased. Predicted temperature patterns at the center of the container profile were lowered in response to the interaction of increased container height and wall TA. As container height decreased, the container wall TA necessary to lower center Tmax to ≤ 40C increased; however, the required increase in TA was greater for Phoenix than for Lexington, principally because of higher ambient air temperatures.
Experiments were conducted from 1989 to 1991 to compare the effectiveness of various cultural techniques in reducing solar injury (SI) and increasing yield of bell pepper (Capsicum annuum var. annuum `California Wonder') in southern Oklahoma. Treatments included black plastic mulch, white plastic mulch, straw mulch, living rye, spunbonded polypropylene used as a plant canopy shade, and bare soil. Marketable yields from plots shaded with spunbonded polypropylene rowcovers were equal to or greater than those from other treatments each year. Two out of 3 years, plots with a black plastic soil mulch had marketable yields lower than those from other treatments. SI was reduced by rowcover shade.
Acute high-temperature stress affects plant protein structure, leading to denaturation and aggregation. Although folding states of individual proteins have been extensively studied, little information is available on protein thermostability in complex mixtures. The objective of this study was to systematically examine protein stabilizing and destabilizing factors in pepper (Capsicum annuum L.) leaf extracts using light transmission measurements. Increasing turbidity and subsequent precipitation were monitored in heated extracts as changes in light scattering at 540 nm. Factors evaluated included leaf tissue concentration, buffer pH, compounds that can stabilize enzymatic activity (chelating agent, complexer of phenolics, and a compatible solute), and destabilizing agents (nonionic detergent and divalent cation). Leaf extract thermostability decreased with increasing tissue concentration from 6 to 60 g fresh weight per liter of buffer. Turbidity and precipitation occurred after exposure to higher temperatures as buffer pH increased from 6.0 to 7.0. Ethylenediaminetetraacetic acid (chelating agent) and polyvinylpolypyrrolidone (complexer of alkaloids and phenolics) had relatively small effects on extract thermostability. Nonionic detergent (Tween 20) destabilized extract thermostability, especially when incorporated in the extraction buffer. Calcium reduced thermostability by about 2 °C when added as CaCl2 at 1 mm. Calcium caused an increase in turbidity that was not directly associated with protein complexes and was not affected by treatment temperature. Mannitol, a compatible solute, increased the temperature at which turbidity and precipitation were induced, but only at high (500 mm) concentrations. Agents that stabilize or destabilize proteins at high temperatures can be assayed in plant extracts by measuring turbidity changes at 540 nm. These findings can be applied to functional studies determining the basis for differences in thermotolerance between genotypes and between control and acclimated tissues.
Previous studies found that high soil temperature is more detrimental than high air temperature for the growth of creeping bentgrass (Agrostis palustris L.). The objective of the study was to investigate changes in fatty acid composition and saturation levels in leaves and roots for creeping bentgrass exposed to high soil temperature. Shoots and roots of `Penncross' plants were subjected to a differential air/soil temperature of 20/35 °C in a growth chamber. Soil temperature was controlled at 35 °C using an immersion circulating heater in water bath. Shoot injury induced by high soil temperature was evaluated by measuring level of lipid peroxidation expressed as malonyldialdehyde (MDA) content, chlorophyll content, and photochemical efficiency (Fv/Fm) of leaves. MDA content increased while chlorophyll content and Fv/Fm decreased at high soil temperature. The content of total fatty acids and different species of fatty acids were analyzed in both leaves and roots. Total fatty acid content in leaves increased initially at 5 days of high soil temperature and then decreased at 15 days, while total fatty acid content in roots decreased, beginning at 5 days. Linolenic acid was the major fatty acid in leaves and linoleic acid and palmitic acid were the major fatty acids in roots of creeping bentgrass. Leaf content of all fatty acid components except oleic acid increased initially and then decreased at high soil temperature. Root content of all fatty acid components except palmitoleic acid and oleic acid decreased, beginning at 5 d of high soil temperature. Oleic acid in leaves and palmitoleic and oleic acid in roots did not change during the entire experimental period. Leaf content of saturated fatty acids and unsaturated fatty acids increased during the first 5 to 10 days of high soil temperature and decreased at 15 and 25 days, respectively. Root content of saturated fatty acids and unsaturated fatty acids decreased beginning at 5 days of high soil temperature. Double bond index decreased in both leaves and roots. High soil temperature induced changes in fatty acid composition and saturation levels in leaves and roots, and this could be associated with physiological damages in leaves even though only roots were exposed to high temperature.
Soil warming is one of the benefits associated with use of plastic film mulches. However, under high temperature conditions during the summer, especially in the southeastern United States, some mulches warm the soil to temperatures that might be deleterious to plant growth. Tomato (Lycopersicon esculentum Mill.) plants grown in the field were exposed to a range of root-zone temperatures (RZTs), resulting from growing the plants in different seasons and by using colored mulches that differed in their soil-warming ability. The objective was to determine the relationship of mean seasonal RZT, as affected by different colored plastic film mulches, with plant growth and fruit yield. The study consisted of experiments carried out in three seasons: Fall 1999 (five mulches, one cultivar), Spring 2000 (eight mulches and three cultivars), and Fall 2000 (four mulches and three cultivars). Treatments were black (n = 2), gray, red, silver (n = 3), and white (n = 2) mulches, and bare soil. Over the season, mean RZT decreased in the fall (from 32 to 24 °C) and increased in the spring (from 20 to 29 °C). Daily mean values of RZT over the season under plastic mulches were higher (1 to 5 °C) than those of air temperature. The highest RZT at midday occurred under black mulch, and the lowest under bare soil and white mulch. Bare soil showed the largest diurnal RZT fluctuation. RZT at midday was up to 4 °C higher under black or gray mulch compared to the other mulches or bare soil. The degree of soil warming was correlated with reflectivity of the mulch. Black mulch had the lowest light reflectance [10% photosynthetically active radiation (PAR)] while silver mulch had the highest (55% PAR). There were, however, differences in reflectance among mulches of the same color depending on the manufacturer. RZT affected vegetative top fresh weight (FW), fruit yield, fruit number, and individual fruit FW. All these growth attributes fitted a quadratic relationship with mean RZT for the season, with an optimal that ranged between 25.4 and 26.3 °C. The effects of colored mulches on plant response depended on the impact of the mulch on RZT. Plant growth and yield were highest as RZT approached the optimal RZT for the plants.
Plants of `Rotundifolia' holly (Ilex crenata Thunb.) were grown for 3 weeks with root zones at 30,34,38, or 42C for 6 hours daily to evaluate the effects of supraoptimal root-zone temperatures on various photosynthetic processes. After 3 weeks, photosynthesis of plants grown with root zones at 38 or 42C was below that of plants grown at 30 or 34C. Chlorophyll and carotenoid levels decreased while leaf soluble protein levels increased as root-zone temperature increased. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) activity per unit protein and per unit chlorophyll responded quadratically, while RuBisCO activity per unit fresh weight increased linearly in response to increasing root-zone temperature. Results of this study suggest that `Rotundifolia' holly was capable of altering metabolism or redistributing available assimilates to maintain CO2 assimilation rates in response to increasing root-zone temperatures.
Growth of tomato (Lycopersicon esculentum Mill.) plants decreases at root-zone temperatures (RZTs) >30 °C, but no research has been conducted on the effects of changes in root respiration on P acquisition at supraoptimal RZT. We monitored the changes every 3 to 5 days in root respiration, root surface phosphatase activity, and P acquisition of `Jet Star' tomato plants grown in Hoagland's no. 1 solution held at 25 and 36 °C RZT for 19 days. Root respiration rate in plants grown at 25 °C increased linearly from RZT initiation to day 12, but there was no difference in respiration between days 12 and 19. Root respiration at 36 °C, however, increased from RZT initiation to day 8 and then decreased. Shoot P concentration and root phosphatase activity for plants grown at 25 °C did not change during the experiment. Shoot P concentration for plants at 36 °C, however, linearly decreased over time, and root phosphatase activity linearly increased over time. Decreased shoot growth and demand for P along with decreased root respiration after day 8 probably resulted in the decreased P uptake and shoot P concentration in plants grown at 36 °C RZT.
Information on the heat resistance of silver maple (Acer saccharinum L.) could help develop stress-resistant Freeman maples (Acer ×freemanii E. Murray). Our first objective was to determine how 26, 30, 32, 34, and 36 °C in the root zone affect growth and water relations of plants from rooted cuttings of a silver maple clone indigenous to Mississippi (33.3 °N latitude). Fresh mass increased over time for plants at all temperatures and was highest for plants with root zones at 30 °C. Quadratic regression functions predicted maximal plant dry mass, leaf surface area, and stomatal conductance at 29, 29, and 28 °C, respectively. Stem xylem water potential (ψ) during the photoperiod decreased linearly with increasing root-zone temperature from -0.83 MPa at 26 °C to -1.05 MPa at 36 °C. Our second objective was to compare six clones of silver maple from the Mississippi location with six clones from 44.4 °N latitude in Minnesota for effects of 35 °C in the root zone on plant growth, stomatal conductance, and stem ψ. Provenance and temperature main effects were significant for most dependent variables, but there were no provenance × temperature interactions. Over both provenances, plant fresh and dry mass, leaf surface area, stomatal conductance, and stem ψ during the photoperiod were higher at 29 than 35 °C. Over both temperatures, plants from Minnesota clones had higher fresh and dry mass and more leaf surface area than plants from Mississippi clones. The lack of temperature × provenance interactions suggests that ecotypic or clinal variation in heat resistance is minimal and will not be useful for identifying superior genotypes for use in interspecific crosses with red maple (Acer rubrum L.).
Abstract
Roots of sour orange (Citrus aurantium L.), ‘Carrizo’ citrange [C. sinensis L. (Osbeck.) × Poncirus trifoliata L. (Raf.)] and ‘Swingle’ citrumelo [C. paradisi Macf. × P. trifoliata L. (Raf.)] seedlings were exposed to various high temperatures for 20 minutes and heat injury was determined by electrolyte leakage procedures, microscopic examination, and visual observations. Temperatures at the midpoint of sigmoidal curves fitted through electrolyte leakage data for excised roots were 51.6° ± 0.5°C, 52.5° ± 0.7°, and 53.5° ± 0.5° for ‘Carrizo’ citrange, sour orange, and ‘Swingle’ citrumelo rootstocks, respectively. Electrolyte leakage results with excised roots were supported by microscopic examination and visual observations of whole plants.
Abstract
Red maple (Acer rubrum L.) plants were evaluated for their responses to 5 weeks of constant root-zone temperatures from 18 to 36C. Shoot lengths of plants grown with 18 to 30C root zones did not differ significantly from one another at any time during the study, and shoot dry weights of these plants were similar. However, after 21 days of exposure, shoot length of plants grown with roots at 36C was significantly less than that of plants with roots grown at 30C and below. Leaf area was greatest among plants with roots at 24C, and mean shoot and root dry weights of plants in the 36C treatment were 57% and 68% less, respectively, than those for plants with roots at 30C. Leaf diffusive resistance of plants grown at 36C was five times greater than for plants with root zones at 30C or below. Shoot water potential decreased with increasing temperature, but increased solute concentration in leaves of 36C-grown plants probably contributed to turgor maintenance.