Effects of Light, Carbon Dioxide, and Temperature on Photosynthesis, Oxygen Inhibition of Photosynthesis, and Transpiration in Solanum tuberosum

Abstract

Individual leaves of potato (Solanum tuberosum L. W729R), a C3 plant, were subjected to various irradiances (400-700 nm), CO2 levels, and temperatures in a controlled-environment chamber. As irradiance increased, stomatal and mesophyll resistance exerted a strong and some-what paralleled regulation of photosynthesis as both showed a similar decrease reaching a minimum at about 85 neinsteins·cm−2·sec−1 (about ½ of full sunlight). Also, there was a proportional hyperbolic increase in transpiration and photosynthesis with increasing irradiance up to 85 neinsteins·cm−2·sec−1. These results contrast with many C3 plants that have a near full opening of stomata at much less light than is required for saturation of photosynthesis.Inhibition of photosynthesis by 21% O2 was nearly overcome by a 2-fold increase in atmospheric levels of CO2 (about 1,200 ng·cm−3). Photosynthesis at 25 C, high irradiance, 2.5% O2 and atmospheric levels of CO2 was about 80% of the CO2-saturated rate, suggesting that CO2 can be rate-limiting even without O2 inhibition of photosynthesis. With increasing CO2 concentration, mesophyll resistance decreased slightly while stomatal resistance increased markedly above 550 ng·cm−3 which resulted in a significant reduction in transpiration.Although potato is a very productive C3 crop, there is substantial O2 inhibition of photosynthesis. The level of O2 inhibition was maximum around 25 C but the percentage inhibition of photosynthesis by O2 increased steadily from 38% at 16 C to 56% at 36 C. Photosynthesis and transpiration showed broad temperature optima (16-25 C). At higher temperatures, both the increased percentage inhibition of photosynthesis by O2 and the increased stomatal resistance limit photosynthesis, while increased stomatal resistance limits transpiration. Water use efficiency, when considered at a constant vapor pressure gradient, increased with increasing irradiance, CO2 concentration, and temperature.