Differences in the Interacting Effects of Light and Temperature on Growth of Four Species in the Vegetative Phase

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Abstract
A comparative study, employing the concepts of growth analysis, has been made of the varying responses in the early vegetative phase of Gossypium hirsutum, Helianthus annuus, Phaseolus vulgaris, and Zea mays to combinations of light intensity (1.08, 2.16, 3.24, 4.32, and 5.4 × 104 lx—photoperiod 14 h) and constant diurnal air temperatures (10, 15, 20, 25, 30, and 35 °C). Depending on the combination of treatments, the temperature of the internal tissues departed from air temperature by 6.9 to 1.4 °C: so only the internal temperatures are cited here. For each species there are complex interactions between the effects of light and temperature on the net assimilation rate, the leaf-area ratio, and the relative growth-rates of plant weight and leaf area. The magnitude of the changes induced by the two factors vary both with the growth component and the species. The temperature responses are maximal up to 20–5 °C while at the highest temperatures they may be negative. The temperature coefficients for leaf-area ratio are consistently less than those of the other three components: here between species the coefficients over 10–20 °C vary by a factor of 9.6, 5.4, and 5.1 for the rates of gain in plant weight and leaf area and the net assimilation rate, while the ordering within each growth component is species dependent. Under conditions of optimal temperature the relative growth-rate and net assimilation rate progressively increase, according to the species, up to either 4.32 or 5.4× 104 lx. The leaf-area ratio is always largest at the lowest intensity. The level of light at which the rate of gain in leaf area reaches a maximum ranges from 2.16× 104 lx for Phaseolus to between 4.32 and 5.40× 104 lx for Gossypium. The highest relative growth-rate and net assimilation rate of Helianthus exceed those of Zea substantially. Indeed the maximal assimilation rate for Helianthus of 2.10 g dm−2 week−1 is the highest ever recorded under field or controlled conditions. Possible reasons for this reversal of the photosynthetic potentials of the two species observed by previous workers are discussed.

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