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- Author or Editor: James E. Shelton x
Seedlings of flame azalea [Rhododendron calendulaceum (Michx.) Torr] were grown for 12 weeks under long-day conditions with days at 18, 22, 26, or 30C for 9 hours in factorial combination with nights at 14, 18, 22, or 26C for 15 hours. Total plant dry weight, top dry weight, leaf area, and dry weights of leaves, stems, and roots were influenced by day and night temperatures and their interactions. Dry matter production was lowest with nights at 14C. Root, leaf, top, and total dry weights were maximized with days at 26C in combination with nights at 18 to 26C. Stem dry weight was maximized with days at 26 to 30C and nights at 22C. Leaf area was largest with days at 18 and 26C in combination with nights at 18 or 26C. Within the optimal, day/night temperature range of 26 C/18-26C for total plant dry weight, there was no evidence that alternating temperatures enhanced growth. Shoot: root ratios (top dry weight: root dry weight) were highest with days at 18 and 30C. Leaf area ratio (total leaf area: total plant dry weight) was highest and specific leaf area (total leaf area: leaf dry weight) was largest when days and nights were at 18C and were lower at higher temperatures. Regardless of day/night temperature, leaf weight ratio (leaf dry weight: total plant dry weight) was higher than either the stem weight ratio (stem dry weight: total plant dry weight) or root weight ratio (root dry weight: total plant dry weight). Net leaf photosynthetic rate increased with day temperatures up to 30C.
Seedlings of mountain laurel (Kalmia latifolia L.) were grown for 16 weeks under long-day conditions with days at 18, 22, 26, or 30C for 9 hours in factorial combination with nights at 14, 18, 22, or 26C for 15 hours. Total plant dry weight, top dry weight, and dry weights of leaves, stems, and roots were influenced by day and night temperatures. The night optimum for all dry weight categories was 22C. Dry matter production was lowest with nights at 14C. Total plant dry weight and dry weights of tops, leaves, and stems were maximized with days at 26C, but for roots the optimum was 22C. Dry weight accumulation was lower with days at 18 or 30C. Responses of leaf area were similar to that of total plant dry weight, with optimum days and nights at 26 and 22C, respectively. Within the optimal day/night temperature range of 22-26/22C for dry weights, there was no evidence that alternating temperatures enhanced growth. Shoot: root ratios (top dry weight: root dry weight) increased with day temperatures up to 30C and were highest with nights at 14 or 26C. Leaf weight ratio (leaf dry weight: total plant dry weight) decreased with increasing night temperature, and increased curvilinearly in response to day temperature with the minimum at 26C. Stem weight ratio (stem dry weight: total plant dry weight) increased with increasing day or night temperature. Root weight ratio (root dry weight: total plant dry weight) was highest with nights at 18 or 22C and decreased with days >22C. Net leaf photosynthetic rate was maximized with days at 26C.