High night temperature tolerance zones: Modeling, predicting, and investigating the effects of high night temperatures on ornamental plant adaptation

The Arnold Zone Map and USDA Hardiness Zone Map are basically used to determine northern limits of plant adaptation within the United States. Similar maps to determine southern limits of plant performance do not exist. Many northern species perform poorly when moved to southern climates and adapt more easily to areas where rapid cooling occurs at night. Night (2000 to 0500 HR) temperature data from four physiographic areas of North Carolina were used to develop threshold temperature curves (May through October). Curves displayed a smooth, continuously differentiable, sigmoid shape between asymptotes at 5 and 30C. Temperature curves were described mathematically using a five-parameter asymptotic model. The mean threshold temperature exceeded by not more than 10% of the maximum threshold hours during June, July, and August was calculated. These values and threshold curves were used to develop a classification scheme for plant high night temperature tolerance zones. Studies were conducted to characterize color loss during the summer of red-leafed seedlings of Acer palmatum Thunb. (Japanese maple), and to determine to what extent night temperatures affect the dark respiration, growth, and anthocyanin expression of A. palmatum 'Bloodgood'. The percentage of seedlings within each of five color classes was determined for five dates from spring to early fall. Shifts in class distribution occurred on every evaluation date. Dark respiration increased 0.09 mg CO...