A Small-Scale Outdoor Plant Growth Chamber with Modulated Enhancement of Solar UV-B Radiation

Abstract

An outdoor, solar illuminated growth chamber with modulated UV-B enhancement, is described and its performance characterized. The chamber was clad with Teflon film that transmitted both UV-A and UV-B with little absorption and whose transmission did not change significantly over 1 yr. An array of UV-B emitting fluorescent tubes with cellulose diacetate filters provided additional UV-B radiation inside the chamber with little additional UV-A, while a similar chamber with unenergized tubes provided an ambient control. Ambient and enhanced UV-B levels were measured using a pair of integrating broad band radiometers, and it was found that frequency modulation allowed control of lamp intensity over a range in excess of 100:1. Within the UV-B chamber, enhanced levels of integrated UV-B could be maintained at a constant ratio over ambient throughout the day. However, it was not sufficient simply to maintain a constant ratio of radiometer output voltages: the angular responses of the two radiometers had to be well matched. The shape of the UV-B portion of the enhanced spectrum closely followed that expected under ozone depleted skies, while the enhancement of UV-A was insignificant. The spectral profile obtained in the UV-B depended on the thickness of the cellulose diacetate filters used to block short wavelength UV radiation emitted by the fluorescent tubes. The number (thickness) of cellulose diacetate filters required to achieve this match varied with season. Although the filters did degrade with exposure to UV-B it was not necessary to replace them for several months. This was due to: (i) low rate of filter degradation because the lamps were rarely required to be run at full brilliance except at midsummer midday; and (ii) increased tube intensity compensated for reduced filter transmission.

Responses of photosynthetic properties and chloroplast ultrastructure of Bryum argenteum from a desert biological soil crust to elevated ultraviolet‐B radiation

“…UV-B supplementation may be supplied by either a square-wave system (Yang et al 2005) or a modulated system (i.e. variable supplemental irradiance over ambient throughout the day, Ryan and Ireland 1997). In addition, it is very important in such studies to ensure a realistic balance between PAR and UV-B (Caldwell et al 1994).…”

Influence of PAR and UV‐A in Determining Plant Sensitivity and Photomorphogenic Responses to UV‐B Radiation ¶†

“…[15] and Vincent and Roy [16]). Results from greenhouse or growth chamber studies and field studies on UV‐B effects are often conflicting (14,21) or difficult to interpret, because of unrealistically high UV irradiation levels, inadequate levels of UV‐A, low PAR or other technical difficulties (14,15,34–40). In general, one observes a reduction in total biomass and plant height with decreasing PAR and increasing UV‐B.…”

“…Outdoor supplementation systems have increased in popularity during the past few years because they provide a method of study that creates only small alterations in the microclimate (2,15,39,40). However, they differ greatly in their methods of operation, equipment, UV‐B exposure regime and experimental design (2,14,15,35,37–39,41–43).…”

Impacts of ambient solar uv (280-400 nm) radiation on three tropical legumes

“…A worldwide decrease of 25-30% in crop yield has also been predicted by UV-B radiation. But the results of UV-B enhancement studies are often difficult to interpret, because of the unrealistically high UV irradiation levels, inadequate levels of UV-A, low photosynthetic photons flux density (PPFD) or other *Corresponding author; fax +91-4562-281338 e-mail ayakuma_99@yahoo.com tPresent address; Research Department of Botany, VHNSN College, Virudhunagar G26 001, India technical difficulties (Edwards, 1992;Adamse et al, 1997;Ryan and Ireland, 1997).…”