The 2011 ASHS Annual Conference

Ultraviolet light in the 280-315 nm waveband (UV-B) is a documented stressor of plants. Several studies have documented UV stress responses, including darker, thicker leaves, increased secondary metabolite production, and plant stunting. In greenhouse production, UV-B is eliminated and UV-A (315-400 nm waveband) is reduced. We sought to determine if short-term doses of UV-A + UV-B on seedlings have a predictable long-term response in altering plant growth and form. Pansy plants with extremely high doses (191 kJ UV-B compared to 18.7 kJ for a summer day of the same duration in Toledo, OH) showed severe and immediate reduction in plant growth and photosystem II efficiency, and in some cases could not recover long-term. However, plants with midrange doses from 40 kJ UV-B to 163 kJ UV-B showed an overall reduction in mass and canopy cover, while maintaining desirable overall plant form; no long-term leaf malformation or discoloration was found. Further, growth and photosynthetic efficiency began to recover approximately 2 weeks after treatment, often catching up to the control groups by the termination of the experiment. Lettuce undergoing the same treatments had similar responses. Based on these results, we believe brief intense doses of UV-A + UV-B lead to immediate changes in plant growth and function, but the effects are largely reversible after several weeks which may have potential in modifying plant growth in greenhouse production.