Dose-Response Studies Assessing the Impact of Atmospheric Ozone On Greenhouse Crops

Worldwide the horticulture industry has become increasingly threatened by air pollutants, especially the pervasive and highly oxidizing gaseous pollutant ozone (O₃) which detrimentally impacts forest, agronomic and horticultural crops. Our prior work documented dangerously elevated levels of ozone exceeding 50 ppb within commercial greenhouses; indoor levels often were greater by up to 1.7-fold that of outdoor ambient air. Here we report biological-assessment results of dose-response studies evaluating the effects of ozone on the growth and development of economically important greenhouse crops. Also reported is the engineering design and implementation of the specialized plant-growth research facility required for these studies. It consists of ten sealed acrylic plant chambers (107 L each) which can be fumigated with ozone-laden air (42 L/min) at prescribed concentrations (0, 40, 80, 120 & 160 ppb O₃). Individual chambers are supplied with conditioned air proportionally blended with ozonated air drawn from a central plenum which is maintained at a fixed concentration (± 5%) over week-long intervals by electronic feedback control of an ozone generator/monitor instrumentation system. The plant chambers, with automated subsurface irrigation, are installed within a 2.7 m x 2.7 m phytotron room which controls lighting, temperature and relative humidity. Studies in the facility have documented the effects of ozone on the development of selected plants, viz., petunia, marigold, impatiens, tomato and lettuce. Parameters evaluated were plant dry-matter accumulation, leaf area, shoot-to-root mass ratios, chlorophyll fluorescence, flowering, and appearance of foliar lesions. Studies assessed ozone effects during plug production (from sown seed to plug size), and for production of plants from plugs to 10-cm pots.