Photosynthesis in the Potato Under Field Conditions.

In spite of the importance of the potato as a food, little is known about the effect of environmental factors on photosynthesis in the plant. Studies with several other crops (1, 12, 16, 23, 24) have not only added to the knowledge of photosynthesis but have aided in understanding certain responses of these crops to environmental variations. VERDUIN and LooMIs (24) and GABRIELSON (10) have shown that saturation light intensity for single, fully exposed leaves is reached at about one-fourth of full sunlight (10,000 + f.c.). THOMAS and HILL (23), working under field conditions, found directly proportional increases in CO2 absorption with up to ten times normal (0.03%o) CO2 in the air. HOOVER, JOHNSTON, and BRACKETT (14) found increases in photosynthesis at light intensities less than 2,000 f.c. as the CO2 content of the air was increased, with indications that both light and CO2 supply may limit photosynthesis at low light intensities. The temperature curve for CO2 absorption under laboratory conditions indicates that the enzymatic reactions (Qlo = 2 or more) may limit the overall rate of the process (9, 17). In the field, however, Q,o values near 1.0 have been demonstrated for photosynthesis within the range of 20 to 400 C (1, 6, 8, 23, 24). Reduction in leaf hydration is assumed to check photosynth1esis. SCHNEIDER and CHILDERS (21) found that CO2 absorption of apple trees held in soil at the wilting percentage dropped to 13%o of optimum. Recovery of optimum rates of CO2 absorption occurred after a period of several days. VERDUIN and LooMIs, (24) observed reduction to 5% of optimum in temporarily wilted maize leaves. Recovery occurred within a few hours after rewatering. MITCHELL (18) found that changes in humidity of surrounding air had little or no effect on photosynthesis. Stomatal closure without wilting did not markedly decrease CO2 absorption. DASTUR (7) observed reductions in photosynthesis with a drop in water content of leaves. The study reported here was planned to measure the effects of physiological and environmental factors on photosynthesis in the potato (Solanum tuberosum L.) under dry-land and irrigation conditions in western Nebraska. Data from earlier experiments have been reported by CHAPMAN (6).