Project at a Glance

Title: Growth and yield effects of ambient air pollution on valencia orange trees

Principal Investigator / Author(s): Olszyk, David M

Contractor: Statewide Air Pollution Research Center, University of California, Riverside

Contract Number: A733-087

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Ecosystem Impacts


This study was conducted to provide detailed information concerning the effects of ambient oxidants [measured as ozone (03)] and added sulfur dioxide (SO2) on young orange trees [Citrus sinensis (L.) Osbeck]. Valencia orange trees were used, as they are grown in areas subject to air pollution and have not been studied for air pollution effects. The exposures were initiated in May 1984 with four chamber treatments: filtered air, filtered air plus 0.09 ppm SO2 (continuously), half-filtered and half-ambient air, and ambient air. Outside control trees were used to determine chamber effects. There were seven trees per treatment. The ambient air pollutant exposures were terminated in August 1988. The SO2 treatment ended in November 1987. Tree response to air pollutants was documented in terms of fruit yield and quality, leaf physiology and biochemistry, and leaf biomass production per tree. Ambient oxidants dramatically reduced orange fruit yields for the first two harvests. A linear equation described the relationship between O3 concentration in the oxidant treatment and orange yields across both years according to the formula: total fruit weight per tree in kg = 53.7 - (261.1 x O3 average). The O3 average was for all hourly values between 0800 and 2000 from April through October during the summer two years before the harvest year. The reduced fruit weight with oxidant exposure was associated primarily with reduced number per tree. Oxidants had little effect on fruit quality except for a slightly less orange color. Orange yields for all treatments decreased in 1988, indicating an "off" productivity year in 1988 vs 410n'1 years in 1986 and 1987. Oxidants had no effect on orange yields or fruit quality in 1988. Ambient oxidants had no effect on overall tree growth, leaf production, innnature fruit loss, or flower drop. Individual leaves weighed less with higher oxidant concentrations. Oxidants resulted in stomata1 closure and more negative leaf water potentials, indicating increased moisture stress to leaves. Net photosynthetic rate was not affected by oxidants. Leaf starch prior to flowering was higher with increasing oxidant concentrations, indicating an effect on carbon allocation which may be affecting flowering or fruit set. No other biochemical indicators were affected by oxidants. Sulfur dioxide (applied continuously to orange trees at approximately 0.09 ppm) reduced fruit yields significantly in 1986 and 1987. Yields for SO2 exposed trees were 23 and 35% lower than for filtered air trees in 1986 and 1987, respectively. The reduced yield for the SO2 trees was associated with both reduced numbers and size of fruit. Sulfur dioxide exposure resulted in more elliptical fruit, but no other quality effects were found. Individual leaves weighed less with SO2 exposure. Sulfur dioxide resulted in a higher leaf transpiration rate than for filtered trees, but had no overall effect on stomatal conductance, net photosynthetic rate, or leaf water potential. Leaf total sulfur concentration was increased with SO2 exposure, but no other biochemical changes were found. The chambers themselves had many effects on the orange trees. Many fruit were produced on chamber trees in 1986, compared to virtually no fruit on outside trees. Weight of fruit was 39% and 106% higher for 1987 a n d 1988, respectively, for ambient chamber trees vs. outside trees. Chamber tree fruit were larger, heavier, and had less acidic juice than fruit on outside trees. Growth and leaf production were much greater for chamber trees than for outside trees. Immature fruit drop was lower, whereas flower production was greater for chamber trees than outside trees. Some physiological and biochemical responses indicated more stress to leaves on chamber trees than to leaves on outside trees, e.g. , higher stomata1 conductance, more negative leaf water potential, and greater leaf starch. Other responses indicated less stress to leaves on chamber trees, e.g., higher photosynthetic rates, higher chlorophyll concentrations, and less weight per unit area compared to leaves on outside trees. Therefore, the results collected to date clearly document the effects of air pollutants on Valencia oranges. However, additional research is needed to determine the impact of the chambers themselves on tree responses and the mechanistic bases for the oxidant and SO2 effects.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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