Effects of Light, Carbon Dioxide, and Temperature on Photosynthesis, Oxygen Inhibition of Photosynthesis, and Transpiration in Solanum tuberosum.
Individual leaves of potato (Solanum tuberosum L. W729R), a C(3) plant, were subjected to various irradiances (400-700 nm), CO(2) 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 (1/2) 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 C(3) 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% O(2) was nearly overcome by a 2-fold increase in atmospheric levels of CO(2) (about 1,200 ng.cm(-3)). Photosynthesis at 25 C, high irradiance, 2.5% O(2) and atmospheric levels of CO(2) was about 80% of the CO(2)-saturated rate, suggesting that CO(2) can be rate-limiting even without O(2) inhibition of photosynthesis. With increasing CO(2) 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 C(3) crop, there is substantial O(2) inhibition of photosynthesis. The level of O(2) inhibition was maximum around 25 C but the percentage inhibition of photosynthesis by O(2) 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 O(2) 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, CO(2) concentration, and temperature.
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Departments of Horticulture and Soil Science, University of Wisconsin, Madison, Wisconsin 53706.
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Tanner
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