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Atmosphere × Canopy Interactions of Nitric Acid Vapor in Loblolly Pine Grown in Open‐Top Chambers
Author(s) -
Taylor G. E.,
Owens J. G.,
Grizzard T.,
Selvidge W. J.
Publication year - 1993
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq1993.00472425002200010010x
Subject(s) - trace gas , chemistry , context (archaeology) , environmental chemistry , atmosphere (unit) , nitrogen , water vapor , canopy , environmental science , atmospheric sciences , horticulture , botany , meteorology , geology , biology , paleontology , physics , organic chemistry
Many studies that address the impact of tropospheric O 3 on agricultural and forested ecosystems utilize the open‐top chamber. During the production of O 3 using electrical discharge generators fed with dry air, there is an inadvertent addition of HNO 3 vapor, a highly reactive trace gas. While several studies have proposed that HNO 3 vapor introduces artifacts, none has measured concentrations of the odd‐N 2 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 O 3 treatments consisted of charcoal‐filtered or subambient (0.96 µ mol m −3 , 24‐h mean), ambient (1.62 µ mol m −3 , 24‐h mean), and elevated (2.36 µ mol m −3 , 24‐h mean) concentrations, the last being accomplished by proportional O 3 addition over the diurnal period. Measurements of the HNO 3 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 O 3 ), an 8.4‐fold range. For every 100 mol of O 3 added to the chamber, 28 mol of HNO 3 vapor were inadvertently added; this ratio is several times higher than that previously reported. This result, taken with published estimates of leaf conductance to HNO 3 vapor, indicates a maximum N deposition in the form of HNO 3 vapor ranging from 19.5 pmol N cm −2 leaf area h −1 (subambient O 3 ) to 171.9 pmol N cm −2 h −1 (elevated O 3 ). Given the nutrient content of the seedlings and knowledge of the fate of HNO 3 vapor on the leaf surface and leaf interior, the degree to which N deposition via HNO 3 vapor met the N requirements of the loblolly pine seedlings was estimated. Seedlings in the elevated O 3 treatment had an upper‐limit estimate of 3.5% for the needles and 1.8% for the whole plant of N derived from HNO 3 vapor. The concentration of HNO 3 vapor in the chambers, site of HNO 3 vapor deposition, N requirements of the loblolly pine seedlings, and estimated threshold for phytotoxic effects of HNO 3 vapor indicate that the inadvertent production of this odd‐N 2 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 O 3 ‐exposure scenarios recognize the potential for inadvertent N deposition, particularly in trees grown in N‐deficient substrate.