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Photosynthesis and Growth Response of Almond to Increased Atmospheric Ozone Partial Pressures¹

Dep. of Viticulture and Enology, Univ. of California-Davis and Kearney Agricultural Center, Parlier, CA 93648;
Dep. of Pomology, Univ. of California, Davis, CA 95616.

^* Corresponding author.

ABSTRACT

Uniform nursery stock of five almond cultivars [Prunus dulcis (Mill) D.A. Webb syn. P. amygdalus Batsch, ev. Butte, Carmel, Mission, Nonpareil, and Sonora] propagated on peach (P. domestica L. Batsch.) rootstock were exposed to three different atmospheric ozone (O₃) partial pressures. The trees were planted in open-top fumigation chambers on 19 Apr. 1989 at the University of California Kearny Agricultural Center located in the San Joaquin Valley of California. Exposures of the trees to three atmospheric O₃ partial pressures (charcoal filtered air, ambient air, or ambient air + O₃) lasted from 1 June to 2 Nov. 1989. The mean 12-h [0800–2000 h Pacific Daylight Time (PDT)] O₃ partial pressures measured in the open-top chambers during the experimental period were 0.038, 0.060, and 0.112 µPa Pa^–1 O₃ in the charcoal filtered, ambient, and ambient + O₃ treatments, respectively. Leaf net CO₂ assimilation, trunk cross-sectional area growth, and root, trunk, foliage, and total dry weight of Nonpareil were reduced by increased atmospheric O₃ partial pressures. Mission was unaffected by O₃ and Butte, Carmel, and Sonora were intermediate in their responses. Foliage of Nonpareil also abscised prematurely in the ambient and ambient + O₃ treatments. The results indicate that there are almond cultivars that are sensitive to O₃ exposure.

¹ This study was funded in part by grants from the Almond Board of California and the California State Air Resources Board. The statements and conclusions of this report are those of the Univ. of California and not necessarily those of the Almond Board of California and/or the California State Air Resources Board. The mention of commercial products, their source, or their use in connection reported herein is not to be construed as either an actual or implied endorsement of said products.

Received for publication June 18, 1991.