C. Ray Thompson

Effects of ozone or sulfur dioxide on growth and yield of rice

Abstract Three cultivars of rice, Oryza sativa, M7, M9 and S201 were exposed in open-top field chambers to ozone and sulfur dioxide to determine the effects of these important air pollutants on field-grown plants. Exposures were for 15 weeks with ozone at 0, 98, 196, 294 or 392 μg m−3 for 5 h day−1, 5 days week−1, and sulfur dioxide at 131, 262, 393 or 524 μg m−3 for 24 h day−1, 5 days week−1. Three harvests of rice were made after 27 and 68 days and at the end of the exposures. At the first harvest following early plant growth, ozone at the highest concentrations resulted in reductions in growth whereas sulfur dioxide resulted in increased growth. At the second harvest, ozone-exposed plants continued to show reduced growth, whereas sulfur dioxide resulted only in reduced plant height. At the final and major harvest, ozone at 392 μg m−3 reduced total seed weight 12, 29 and 21% in cultivars M7, M9 and S201, respectively. Weight of 100 seeds and straw weight were reduced in M9 and S201 and percent seed sterility in panicles was increased. Ozone reduced height of all cultivars and increased the number of panicles. Sulfur dioxide at 524 μg m−3 reduced total seed weight of M9 and S201 by 22 and 14%, respectively, and weight per hundred seed by 11 and 10%, respectively. The results showed that ozone is much more injurious to rice per unit of pollutant than sulfur dioxide and that reduced yield due to both pollutants was caused mostly by reduced seed size. Increased seed sterility was partially offset by ozone exposure of the plants which produced more panicles. Cultivar M7 was more resistant to ozone or sulfur dioxide than M9 and S201.

Effect of H2S Fumigation on Water-Soluble Sulfhydryl Compounds in Shoots of Crop Plants

Summary Long-term exposure of Spinacea oleracea and Beta vulgaris to 30, 100 and 300 ppb H 2 S resulted in reduced plant growth at 300 ppb and in an increased water-soluble sulfhydryl-compound content of shoots, even at an exposure to 30 ppb H 2 S. The increase in water-soluble sulfhydryl compounds was noticed during the entire 44 day fumigation period, in spite of ageing of the plants which caused a decrease of the actual sulfhydryl content of the control plants. The increase of sulfhydryl content in spinach was due to an accumulation of glutathione. Already after three days of exposure to 250 ppb H 2 S, the glutathione level in the shoot was increased more than four-fold. The significance of glutathione accumulation during H 2 S exposure for plant metabolism and growth is discussed.

The Effect of Light on Predisposing Plants to Ozone and Pan Damage

Experiments were carried out to examine the importance of light as a factor influencing the type and amount of smog damage to plants. The stomatal action of leaves under various light conditions and the correlation of stomatal opening to plant damage from atmospheric pollutants were studied. Results indicated that some other factor than stomates was more important in controlling plant susceptibility to smog. The differences in plant response of various age bean plants suggested that the mechanism of ozone damage is quite different from PAN damage. The relationships between sugar production and ozone damage are examined. 9 references, 11 figures, 2 tables.

Crop loss assessment for California: modeling losses with different ozone standard scenarios.

Crop yield losses were estimated for ambient O3 concentrations and for a series of potential O3 air quality standards for California, including the current statewide 1-h oxidant (O3) standard of 0.10 ppm (196 microg m(-3)), 12-h growing season averages, and other models. A model for statewide losses was developed using hourly O3 data for all sites in the State, county crop productivity data, and available O3 concentration-yield loss equations to determine potential yield losses for each crop in each county in California for 1984. Losses were based on comparison to an estimated background filtered air concentration of 0.025 or 0.027 ppm, for 12 or 7 h, respectively. Potential losses due to ambient air in 1984 were estimated at 19% to 25% for dry beans, cotton, grapes, lemons, onions, and oranges. Losses of 5% to 9% were estimated for alfalfa and sweet corn. Losses of 4% or less were estimated for barley, field corn, lettuce, grain sorghum, rice, corn silage, spinach, strawberries, sugar beets, fresh tomatoes, processing tomatoes, and wheat. Implementation of either a modified rollback to meet the current 1 h California O3 standard (0.10 ppm) or a three-month, 12-h growing season average of 0.045 ppm was necessary to produce large reductions in potential crop losses.

Effects of SO2 on physiology, elemental content and injury development of winter wheat

Abstract The effects of sulfur dioxide on buffering capacity, chlorophyll content, stomatal conductance, mineral composition and leaf injury of winter wheat ( Triticum aestivum , cv. Yecora Rojo) were studied. Plants were exposed to sulfur dioxide (0, 79, 183, and 393 μg m −3 ) in open-top chambers. Exposures were conducted in Riverside, California, during the coolest part of the year when the plants are believed to be more sensitive to sulfur dioxide than during the rest of the year. Physiological measurements, injury rating and collection of leaf material for chemical analysis were carried out after 22 days of exposure. The results of these measurements were compared with yield data from the final harvest which took place after 118 days of exposure. Elevated SO 2 concentrations caused decrease of buffering capacity, increase of total sulfur content and increase of injury of wheat leaves. These changes correlated significantly with reduction of total seed weight and weight of 100 wheat seeds at the final harvest. Stomatal conductance to water vapor, chlorophyll content and two leaf mineral concentrations (calcium, potassium) were not significantly affected by sulphur dioxide exposure. The results of this study indicated that buffering capacity, total sulfur content and injury of leaves could be used as early indicators of SO 2 stress in wheat and its subsequent yield losses.

An improved diffusion method for determining submicrogram amounts of fluoride in biological samples

Abstract A method for fluoride determination has been developed in which a level of 0.0–2.5 μg fluoride was determined quantitatively from several milligram samples of biological material. This technique allows the drying, ashing, and diffusion of small samples without transfer. The SPADNS-zirconium lake is a sensitive and convenient color reagent. Recoveries of 96 to 102% were obtained.

A simplified fluorometric fluoride analyzer

Abstract A fluorometric fluoride analyzer previously described (Ivie et al ., 1965) has been redesigned and simplified to provide a more usable instrument. A single photomultiplier tube is used to receive alternate light pulses rather than the two tubes used formerly. Illumination of the sensitized tape is accomplished by two ultraviolet lamps. The electronic circuitry for tape illumination and carrying of signals to the recorder has been simplified. A light “piping” system improves light transmission and the bulk and weight of the overall equipment has been reduced to about one-half.

Humidity as a Modifier of Vegetation Responses to Ozone: Design and Testing of a Humidification System for Open-Top Field Chambers

A system was designed, constructed, and tested for increasing the relative humidity in open-top field chambers used for air pollution studies. The system consisted of a propane-fired steam boiler capable of generating 454 kg hr−1 of dry steam at 0.1055 g cm−2 (15 PSI), ducting to supply humidified air to open-top chambers, and humidistats to control the humidity level In each chamber. Performance tests showed that under warm, dry conditions (air temperatures of 30°C and ambient relative humidity of 10 percent) the humidity level could be increased by 43 percent in each of two chambers or 25 percent in each of six chambers. At higher ambient humidities or cooler ambient temperatures, greater increases in relative humidity could be achieved. Temperature rise in the humidified chambers was 2.0-4.5°C vs. nonhumidified chambers on warm days due to the injected steam and solar heating of the galvanized steel ducting. Insulating the ducting reduced this difference to 1.6- 2.3°C. Bean plants (Phaseolus vulgaris) ...