The effect of temperature on the growth of S.170 tall fescue (Festuca arundinacea). 2. Independent variation of day and night temperatures.
Young plants of S170 tall fescue were grown in different day/night temperature regimes in most combinations of 10, 15, 20, 25 and 30 deg C in 4 series of experimental treatments. Leaf width, number of externally visible leaves growing on a shoot at the same time, and N content of the plants were little affected by temperature. Tiller number and water-soluble carbohydrate content of the plants were increased by lowering either the day or the night temperature while holding the other constant at 20 deg . When the mean day/night temperature was maintained at 20 deg , higher values of these 2 parameters were reached in the 20 deg /20 deg regime than in any other. The duration of growth of an individual leaf and the time interval between the appearance of successive leaves were reduced equally by raising the temperature of either the day or night to 25 deg , but not 30 deg , while keeping the other at 20 deg . All but one of the remaining parameters (lamina length and area, sheath length, rate of leaf growth, LAR, specific leaf area, leaf weight ratio, NAR, relative rate of leaf area increase and RGR) achieved maximum values in the 25 deg /25 deg regime and were more affected by the day temperature than by that of the night. When the night temperature was held at 20 deg , the optimum day temperature for NAR, RGR and relative rate of leaf area increase was also about 20 deg , whereas for the other growth attributes it was about 29 deg . In a mean temperature of 20 deg all attributes achieved maximum values when the day temperature exceeded that of the night by 4-10 deg ; when the night temperature was kept below its optimum of 25 deg , a higher day temperature usually favoured growth, and when a suboptimum mean temperature was maintained, raising the day temperature favoured growth more than lowering the night temperature depressed it. When the day temperature was optimum at 25 deg , or slightly suboptimum at 20 deg , the optimum night temperature was equal to that of the day. When the day temperature was markedly suboptimum at 10 or 15 deg , a higher night temperature favoured growth. Only when the day temperature was supraoptimum at 30 deg was a lower night temperature beneficial. There was no evidence that this material, grown in these conditions, responded to temperature in accord with the concept of thermoperiodicity.