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A Supplemental Ultraviolet-B Radiation System for Open-Top Field Chambers

USDA-ARS/North Carolina State Univ. Air Quality Res. Lab. and Dep. of Botany, Box 7632, North Carolina State Univ., Raleigh, NC 27695

E.L. Fiscus and J.E. Miller

USDA-ARS and Dep. of Crop Science, North Carolina State Univ.

R.B. Philbeck

USDA-ARS, North Carolina State Univ.

A.S. Heagle

USDA-ARS and Dep. of Plant Pathology, North Carolina State Univ.

W.W. Heck

USDA-ARS and Dep. of Botany, North Carolina State Univ.

^* Corresponding author.

ABSTRACT

Studies suggest that increased ultraviolet-B (UV-B) radiation at the earth's surface due to stratospheric ozone (O₃) depletion may affect crop production. Current levels of tropospheric O₃ are known to decrease crop yields. To assess the combined effects on plants of increased UV-B radiation and chronic exposure to O₃, a commonly used constant-addition supplemental UV-B radiation system was modified for use in open-top field chambers. Lamp banks containing 14 filtered UV-B-313 fluorescent lamps were suspended in 33 chambers to which either charcoal-filtered, nonfiltered, or nonfiltered air plus O₃ was added. Lamp banks provided ample levels and distribution of biologically effective UV-B (UV-B_BE) radiation for stimulating up to a 29% loss of column O₃, according to a radiative transfer model. However, ground-based measurements of solar UV-B_BE radiation provided a more realistic base than the model for simulations of column O₃ loss using supplemental UV-B radiation. Shading by the lamp bank and chamber assembly reduced the daily solar UV-B_BE, UV-A, and visible irradiances inside the chamber on average by 24% ± 5% compared with ambient levels. Biweekly adjustments of the supplemental UV-B_BE irradiance level and exposure period provided treatments that were proportional to the seasonal trend in solar UV-B_BE radiation. Control of supplemental UV-B_BE irradiance in proportion to solar UV-B_BE irradiance during the day would better simulate the effects of stratospheric O₃ depletion. However, the constant-addition system was a simpler and less expensive method than the proportional-addition system for examining the relative sensitivity of plants to the combined effects of increased UV-B radiation and O₃ under field conditions.