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`Ostinata' Butterhead lettuce (Lactuca sativa L.) was used to study lettuce production at varied shoot (air) and root (pond) temperatures. A floating hydroponic system was used to study the influence of pond temperature on lettuce growth for 35 days. Pond water temperature setpoints of 17, 24, and 31 °C were used at air temperatures of 17/12, 24/19, and 31/26 °C (day/night). Pond temperature affected plant dry mass, and air temperature significantly affected growth over time. Maximum dry mass was produced at the 24/24 °C (air/pond temperature) treatment. Final dry mass at the 31/24 °C treatment did not differ significantly from the 24/24 °C treatment. The 24 °C pond treatment maintained market quality lettuce head production in 31 °C air. Using optimal pond temperature, lettuce production was deemed acceptable at a variety of air temperatures outside the normal range, and particularly at high air temperatures.

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The medicinal plant industry is under increasing scrutiny due to wide variance in active ingredient (AI) concentration from values claimed on labels. Reasons for this disparity include environmental and genotypic variation which influence AI concentration. St. John's wort (Hypericum perforatum) is a popular herbal remedy which also exhibits marked variance in AI concentration among products. This study evaluated concentration changes of three biologically active metabolites of H. perforatum after exposure to UV light while plants were still vegetative. Treatments were performed with 55-day-old plants grown under 400 μmol m(-2) s(-1) PAR for 16 h a day. Three UV light treatments were evaluated: a single dose, a daily dose and an increasing daily dose. Concentrations of hyperforin, pseudohypericin and hypericin were monitored for 7 days after each treatment. A daily dose and an increasing daily dose did not produce significantly greater increases in secondary metabolites compared to single dose treatments. These results suggest the small but significant transient metabolite concentration increases in H. perforatum can be induced by UV light exposure. Information from this study can be useful in optimizing total biomass and metabolite production in controlled environments.