Research Program Area: Ecosystem & Multimedia Effects
Topic Areas: Ecosystem Impacts
The Statewide Air Pollution Research Center has a continuing mission to investigate the effects of air pollutants on agricultural crops, and to determine the amount of losses caused by these pollutants. To further this mission we continued and built upon the project to investigate the chronic physiological, growth, and productivity effects of ambient photochemical oxidants [(measured as ozone (O3)] or sulfur dioxide (SO2) on Valencia orange trees (Citrus Sinensis). The exposure were initiated in May 1984, with four chamber treatments: filtered air, filtered air plus 0.10 ppm SO2 continuously, half filtered and half ambient air, ambient air. Outside control trees were used to determine chamber effects. There were seven trees per treatment. Tree response to air pollutants was documented in terms of fruit yield and quality, leaf physiology and biochemistry and leaf biomass production per tree.
Ozone resulted in statistically significant reductions in fruit yield and alterations in fruit quality. Yield was reduced by 27% in ambient air, and by 10% in half ambient air compared to filtered air. The reduction in yield with the three O3treatments (filtered, half filtered, ambient air) fit a linear O3 concentration vs. fruit weight per tree equation: yield = 69.997 - (O3 concentration x 300.5). The O3 concentration was the seven month (April-October) growing season average for 1986. Sulfur dioxide reduced yields by 35% compared to filtered air. The reduced yields with both O3 and SO2 were due primarily to reduced fruit number and not reduced fruit weight. Fruit quality effects due to SO2 were reduced orange color, increased fruit circumference, and increased rind thickness. The chambers themselves did not affect yield, but did result in altered fruit quality based on comparisons between ambient chamber and outside trees.
Sulfur dioxide resulted in reduced leaf drop on occasional monthly as well as seasonal and yearly basis. Neither ozone nor the chambers effected leaf drop, and no treatment had any effect on individual leaf weights or fruit drop. In terms of physiology, ozone reduced stomatal conductance during summer months and on a whole year basis. Trees in ambient chambers tended to show indications of greater water stress than outside trees. This was indicated by the lower stomatal conductances for ambient chamber trees during summer months and on a whole year basis, and by the more negative leaf water potentials for nine dates, and on winter, summer, and a whole year basis. Sulfur dioxide did not affect physiology and no treatment affected photosynthesis. The primary biochemical effects were a trend toward higher chlorophyll content, and lower specific leaf area for ambient chamber compared to outside trees.
While the results collected to date clearly document the effects of air pollutants on Valencia oranges, additional research is needed to determine the impact of the chambers themselves on tree response and the mechanistic bases for the O3 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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