Growth temperature influences the underlying components of relative growth rate: an investigation using inherently fast- and slow-growing plant species

We examined the effect of growth temperature on the underlying components of growth in a range of inherently fast- and slow-growing plant species. Plants were grown hydroponically at constant 18, 23 and 28 degreesC. Growth analysis was conducted on 16 contrasting plant species, with whole plant gas exchange being performed on six of the 16 species. Inter-specific variations in specific leaf area (SLA) were important in determining variations in relative growth rate (RGR) amongst the species at 23 and 28 degreesC but were not related to variations in RGR at 18 degreesC. When grown at 18 degreesC, net assimilation rate (NAR) became more important than SLA for explaining variations in RGR. Variations in whole shoot photosynthesis and carbon concentration could not explain the importance of NAR in determining RGR at the lower temperatures. Rather, variations in the degree to which whole plant respiration per unit leaf area acclimated to the different growth temperatures were responsible. Plants grown at 28 degreesC used a greater proportion of their daily fixed carbon in respiration than did the 18 and 23 degreesC-grown plants. It is concluded that the relative importance of the underlying components of growth are influenced by growth temperature, and the degree of acclimation of respiration is of central importance to the greater role played by NAR in determining variations in RGR at declining growth temperatures.