Effect of Soil-Moisture Content on the Rate of Photosynthesis and Respiration in Ladino Clover (Trifolium Repens L.).

Abstract

A special apparatus used for controlling the environment of plant material consisted essentially of a metal box which was provided with air exchange facilities, a plastic top for admitting light and a recess for a 3-liter soil container. Rates of photosynthesis were computed from the CO2 exchanged as measured titri-metrically. Plants irrigated when approximately 80% of the soil-moisture held between the moisture equivalent and the permanent wilting percentage had been extracted showed no change in photosynthetic activity preceding or following irrigations. No reduction in the rate of photosynthesis was detected as soil moisture was extracted, until the approximate time the first visible signs of wilting appeared. When plants were distinctly wilted, photosynthetic activity had been reduced to approximately 75% of its maximum value. Severely wilted plants showed 40 to 60% increases in rates of photosynthesis within six hours after irrigation. Experiments under continuous light supported these conclusions. Increases in respiration noted as wilting appeared were relatively much smaller than the accompanying changes in photosynthesis.