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Journal of Environmental Quality Abstract -

Atmosphere × Canopy Interactions of Nitric Acid Vapor in Loblolly Pine Grown in Open-Top Chambers


This article in JEQ

  1. Vol. 22 No. 1, p. 70-80
    Received: Jan 20, 1992

    * Corresponding author(s):
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  1. G. E. Taylor Jr. *,
  2. J. G. Owens,
  3. T. Grizzard and
  4. W. J. Selvidge
  1. Biological Sciences Center, Desert Res. Inst., P.O. Box 60220, Reno, NV 89506, and Dep. of Environ. and Resour. Sci., Univ. of Nevada-Reno;
    Environ. Sciences Division, Oak Ridge National Lab., P.O. Box 2008, Oak Ridge, TN 37831.



Many studies that address the impact of tropospheric O3 on agricultural and forested ecosystems utilize the open-top chamber. During the production of O3 using electrical discharge generators fed with dry air, there is an inadvertent addition of HNO3 vapor, a highly reactive trace gas. While several studies have proposed that HNO3 vapor introduces artifacts, none has measured concentrations of the odd-N2 trace gas in the chamber or investigated the fate of the N in the context of whole-plant physiology and growth. These questions were investigated using open-top chambers containing seedlings of loblolly pine (Pinus taeda L.) during the 1988 growing season in Oak Ridge, TN. The O3 treatments consisted of charcoal-filtered or subambient (0.96 µmol m−3, 24-h mean), ambient (1.62 µmol m−3, 24-h mean), and elevated (2.36 µmol m−3, 24-h mean) concentrations, the last being accomplished by proportional O3 addition over the diurnal period. Measurements of the HNO3 vapor concentration during dry periods only (no rainfall or ground-level fog) averaged 28.6 nmol m−3 (subambient), 55.4 nmol m−3 (ambient air), and 240.0 nmol m−3 (elevated O3), an 8.4-fold range. For every 100 mol of O3 added to the chamber, 28 mol of HNO3 vapor were inadvertently added; this ratio is several times higher than that previously reported. This result, taken with published estimates of leaf conductance to HNO3 vapor, indicates a maximum N deposition in the form of HNO3 vapor ranging from 19.5 pmol N cm−2 leaf area h−1 (subambient O3) to 171.9 pmol N cm−2 h−1 (elevated O3). Given the nutrient content of the seedlings and knowledge of the fate of HNO3 vapor on the leaf surface and leaf interior, the degree to which N deposition via HNO3 vapor met the N requirements of the loblolly pine seedlings was estimated. Seedlings in the elevated O3 treatment had an upper-limit estimate of 3.5% for the needles and 1.8% for the whole plant of N derived from HNO3 vapor. The concentration of HNO3 vapor in the chambers, site of HNO3 vapor deposition, N requirements of the loblolly pine seedlings, and estimated threshold for phytotoxic effects of HNO3 vapor indicate that the inadvertent production of this odd-N2 trace gas is important in understanding the atmospheric chemistry within the chambers, but that the level of N loading in this study is unlikely to affect physiology or growth. However, we recommend that studies that employ higher O3-exposure scenarios recognize the potential for inadvertent N deposition, particularly in trees grown in N-deficient substrate.

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