The influence of temperature, nutrient status, and short drought on seasonal initiation of primordia and shoot elongation in Pinusradiata

Abstract

Effects of temperature-related conditions on primordial initiation and shoot elongation were studied using rooted cuttings of mature Pinusradiata D. Don grown for 12 months in two field locations and three controlled environments. In two of the controlled environments, mean monthly temperatures of the respective field sites were simulated and in the third, a constant day–night temperature regime was set up. For each of the controlled environments there were four subtreatments: (i) frost, (ii) water deficit, (iii) supplementary nutrients, and (iv) control. Plants in relatively warm environments, both field and laboratory, produced more primordia, elongated more, and showed greater apical dominance than those in cool conditions. In the cooler environments, formation of lateral shoots tended to occur later in the growing season. Water deficit and supplementary nutrient subtreatments did not significantly affect growth. Exposure to light frosts reduced internode elongation of the leading shoots of plants grown at relatively warm temperatures. Quantitatively there were significant differences between field- and laboratory-grown plants. Annual primordial production in the field and shoot elongation were 2 and 3 times that obtained under controlled conditions, respectively. Apical dominance in the field was much more pronounced than in the controlled environment. However, the types and patterns of morphological response to temperature were similar in both field and laboratory plants.