The influence of growing temperature on photosynthesis and respiration of Pinus radiata seedlings

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Abstract
Rates of photosynthesis at five light intensities and rates of respiration at four temperatures, 9°, 16°, 24° and 30°C were measured in three P. radiata seedlings from each of the growing conditions 15°/10°, 24°/19°, and 33°/28°C day/night temperatures. Net photosynthesis at 30° and 9°C was reduced in seedlings grown under the cold and the two warmer preconditioning treatments respectively. Sixteen degrees appeared to be the optimum temperature for net photosynthesis in seedlings grown at 15°/10° and 24°/19°C, with 24°C being the optimum for the plants raised at 33°/28°C. Photosynthesis per seedling increased by almost 35% and rates of respiration were approximately halved within two days of the seedlings being transferred from 15°/10° to 33°/28°C. In that transfer (and also the reverse of it, i.e. 33°/28° to 15°/10°C in which photosynthesis dropped by some 25%) most of the adaptation of each seedling occurred within two days, and within a few days more the seedlings were similar in behaviour to seedlings which had been raised entirely under the changed temperature conditions.