EFFECT OF TEMPERATURE ON PHOTOSYNTHESIS AND RESPIRATION IN RED AND LOBLOLLY PINES

Abstract

Apparent photosynthesis and respiration were measured in seedlings of loblolly pine (Pinus taeda) and red pine (P. resinosa) at 20[degree], 30% and 40[degree] C. A light intensity of 4500 ft.-candles was used for the measurement of photosynthesis. The rates of apparent photosynthesis of the 2 spp. were approx. the same at 30[degree] as at 20[degree] C, but decreased about 45% when the temp, was increased from 30 to 40[degree]. The rate of respiration of both spp. doubled when the temp, was increased from 20[degree] to 30[degree] C and increased about 50% cent from 30 to 40[degree]. The ratio of photosynthesis to lespiration for both spp. was about 13 at 20% 6.8 at 30 and only 3 at 40[degree] C. Supplementary measurements of photosynthesis at a light intensity of 9300 ft.-candles and temps, of 19[degree] and 32[degree] C showed no significant difference in the behavior of the 2 spp. The ratios of photosynthesis to respiration showed the same proportional decrease with increasing temp, in both spp. There was no indication of a gross disturbance of the photosynthetic-respiratory balance of red pine at high temp. that might explain the retarded growth of this sp. south of its normal range.