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Physiology and Biochemistry

The Influence of Soil Fertility and Water Stress on the Ozone Response of Hybrid Poplar Trees. Ronald Harkov, Graduate student, Department of Plant Pathology, Cook College, Rutgers-The State University, New Brunswick, NJ 08903; Eileen Brennan, professor, Department of Plant Pathology, Cook College, Rutgers-The State University, New Brunswick, NJ 08903. Phytopathology 70:991-994. Accepted for publication 9 April 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-991.

Experiments were conducted to determine the role of soil fertility and water stress on the ozone response of hybrid poplar trees. Rooted cuttings of hybrid poplar clone #388 (Populus maximowiczii × P. trichocarpa) were grown in a filtered-air greenhouse in 4.73-L plastic pots containing a greenhouse potting mix. A slow release 18-6-12 NPK fertilizer was added to obtain four soil fertility levels. Although the nitrogen content of the foliage increased significantly, after 2 mo of growth, neither linear growth nor percent dry weight was affected by these amendments. Trees with a foliar content of approximately 2.69% N were found to be more susceptible to ozone fumigation of 196 μg/m³ for 6 hr than were trees with 1.53, 3.12, or 3.47% N. In the water stress experiment, withholding water from the test plants for 6–9 days reduced the relative water content in the foliage to 7–21%, respectively, below that of control plants, and protected the trees from a 6-hr fumigation at 196 μg/m³. Visible water stress symptoms were not evident in plants from which water had been withheld for 6 days. These results are discussed as they pertain to susceptibility of urban trees to ozone damage.