Search Results

You are looking at 1 - 3 of 3 items for :

  • Author or Editor: W.A. Retzlaff x
  • HortScience x
Clear All Modify Search

Japanese plum (Prunus salicina Lindel., `Casselman') trees were enclosed in open-top chambers on 1 May 1989 and exposed to three atmospheric ozone partial pressures (charcoal-filtered air [CF], ambient air [AA], and ambient air+ozone [AO]) during the growing season in 1989, 1990, 1991, and 1992. The mean 12-h (0800-1900 HR PDT) ozone partial pressures during 1992 were 0.027, 0.045, and 0.087 μPa Pa-1 in the CF, AA, and AO treatments, respectively. Both stem and leaf water potential (Ψ) decreased from 0700 to 1600 HR PDT and were lowest at midday (1200-1400 HR PDT) in all ozone treatments. Leaf and stem were equivalent at predawn, but leaf Ψ was lower than stem Ψ during the diurnal period. Midday stem Ψ was greater in the AA and AO treatments compared to the CF treatment. Before 1 Aug., stomatal conductance of trees in the AO treatment was reduced compared to the CF treatment, but diurnal fluctuations were similar between the two treatments. Following 1 Aug., stomatal conductance of trees in the AO treatment was reduced compared to the CF treatment, but stomatal conductance of the AO treatment remained the same throughout the day. Trees in the AO treatment had greater leaf fall earlier in the growing season than those of the other treatments. Changes in plum tree stem Ψ under chronic ozone stress are probably due to a loss (early senescence) of transpiring leaf area as well as declines in stomatal conductance.

Free access

Japanese plum (Prunus salicina Lindel. `Casselman') trees exposed to three atmospheric ozone partial pressure treatments were sprayed with a summer application of Volck Supreme oil (1% aqueous solution) to control an outbreak of spider mites (Tetranychus spp.). Phytotoxic effects were observed on the foliage of trees in the plots exposed to ambient or higher atmospheric ozone partial pressures 5 days following spray application. Foliage on trees exposed to 0.044 and 0.081 μPa·Pa-1 ozone [12-h mean (8 Apr. to 12 June 1992)] partial pressures developed water spotting and more foliage abscission than trees exposed to charcoal-filtered air (0.024 μPa·Pa-1 ozone). Thus, ozone air-pollution stress may predispose plants to increased phytotoxicity from summer oils.

Free access

Models indicate that ozone inhibits carbon assimilation largely in the upper canopy, due to light and ozone gradients. We document yield reductions and ozone gradients in Casselman plum in open-top ozone fumigation chambers. Ambient air (12 hr mean ozone = 0.050 ppm), charcoal filtered air (0.034 ppm) and ambient air plus added ozone (0.094 ppm) were circulated in the chambers. Additional trees grew outside the chambers (0.058 ppm). Outside the chambers large vertical and horizontal gradients in ozone within the canopy were documented, but these were absent in the chambers. Ozone decreased leaf photosynthesis by 31% and 58%, and fruit yield by 20% and 66%, in the ambient and ozone enriched relative to filtered chambers. Despite altered gradients, yield and photosynthesis of exposed leaves were similar inside and outside the chambers in ambient air. Compensatory changes in leaf function may be involved.

Free access