Evolutionary interpretation of a high temperature growth response in five New Zealand forest tree species

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Abstract
A controlled environment experiment was undertaken to determine optimum growing temperatures for rimu (Dacrydiwn cupressinum Lamb.), kahikatea (Dacrycarpus dacrydioides (A.Rich.)DeLaub.), totara (Podocarpus totora G.Benn. ex Don), kauri (Agathis australis Salisb.), and mountain beech (Nothofagus solandri var. cliffortioides (Hook.f.)Poole) at three light intensities. Light intensity had no significant effect on the growth of any of the five species. All species achieved maximum growth at a day temperature of 27°C, and at night temperatures of 22°C or 27°C. Significant differences in growth occurred for all species between the five temperature regimes examined. All species showed a significant difference in net photosynthetic rate between temperature regimes. Rimu, kahikatea, totara, and kauri experienced maximum net photosynthetic rates in one of the 27°C regimes. Mountain beech had a maximum net photosynthetic rate in the 21°C regime. Both rimu andbeech allocated significantly more photosynthate to leaves at 27°C than at 21°C day temperatures. The optimal temperatures for photosynthesis and growth are much higher than reported for other temperate species. It is suggested that this attribute evolved in the subtropical climates of the Miocene, and has remained as a relic trait to the present. The significance of this is discussed, with particular reference to timberlines.