Effect of high temperature on photosynthesis in potatoes

The effect of high temperatures on the rate of photosynthesis was studied in several potato varieties. Temperatures of up to 38 °C did not cause a reduction in the photosynthesis of plants that had been grown at these temperatures for long periods prior to measurement. Higher temperatures of 40-42 °C, or the transfer of plants from daytime temperature regimes of 22 °C to 32 °C, caused a reduction in net photosynthesis. This reduction was found to be essentially mesophyllic in origin. High temperature was found to be associated with a decrease in stomatal resistance, an increase in transpiration, and a larger difference between air and leaf temperatures. Dark respiration rates and compensation points for CO₂ concentration were also greater at the high temperatures. It was concluded that the potato crop can be adopted to grow and have an adequate rate of photosynthesis even at relatively high temperatures. Source-sink relationships, which were modified by the later formation of tubers at higher temperatures, did not affect photosynthesis in this study. Varietal differences in resistance to heat stress were observed, with the clone Cl-884 showing a more efficient capacity for photosynthesis at temperatures up to 40 °C than many commonly grown varieties.