2018 ASHS Annual Conference

Detailed study in highly controlled environments featuring active temperature maintenance and supplemental lighting has helped explain the influence of light and temperature on lettuce primary productivity and secondary metabolite levels. However, crop responses in moderately and passively manipulated environments important to a large and increasing number of growers are less clear. Responses by high tunnel-grown baby red lettuce experiencing diurnal temperature fluctuations modified by day and/or night aerial coverings during the dynamic spring and fall periods are particularly under-investigated. In this study, twenty 4.47-m² wood-framed beds containing a soil-based medium within a 9.1 m x 24.4 m single-layer high tunnel at The OSU-OARDC in Wooster, OH, were seeded with ‘Outredgeous’ lettuce (Lactuca sativa) on October 27, 2017, and February 20, 2018. Each bed contained 14 rows (1.2 g seed/row) spaced 7 cm apart. One week after seeding, beds were assigned to one of four treatments (high day/high night - H/H, high day/ambient night - H/A, ambient day/high night - A/H, and ambient day/ambient night - A/A) arranged in a randomized complete block design with five replications. “High” daytime temperatures were achieved by covering beds with vented 0.1524-mm thick polyethylene film, while “high” nighttime temperatures were achieved by covering beds with 50-AG Agribon fabric, both supported by standard low tunnel hoops. Thus, individual beds were either uncovered or covered with film during the day (approx. 08:00 – 17:00; all treatments) and either uncovered (A/A) or covered with film (H/A), fabric (A/H) or both materials (H/H) during the night. Canopy temperature was recorded every 15 minutes in all beds using HOBO U23-Pro Data Loggers throughout the seven weeks of each experimental run, with spontaneous readings of canopy light intensity (PAR) taken eight times over the experimental period. All vegetative tissue 1 cm above the soil line was removed from a 0.25-m² area/bed four weeks after seeding and a 0.18-m² area/bed seven weeks after seeding for measures of fresh and dry weight, total soluble solids (⁰Brix), leaf area and total anthocyanin concentration (Week 7 only). Samples were also included in sensory panel evaluation (discrimination tests based on color only) beginning in Spring-2018. The experiment will be repeated in Fall-2018 and Spring-2019. Differential day- and nighttime coverings resulted in treatment differences in diurnal temperature profiles in Fall 2017. Preliminary analysis indicates a significant positive relationship between day and night temperatures and Week 7 sample fresh weight (g), dry weight (g) and leaf area (cm²).