The Effect of Temperature on the Occurrence of O2 and CO2 Insensitive Photosynthesis in Field Grown Plants

Abstract

The sensitivity of photosynthesis to O2 and CO2 was measured in leaves from field grown plants of six species (Phaseolus vulgaris, Capsicum annuum, Lycopersicon esculentum, Scrophularia desertorum, Cardaria draba, and Populus fremontii) from 5.degree. C to 35.degree. C using gas-exchange techniques. In all species but Phaseolus, photosynthesis was insensitive to O2 in normal air below a species dependent temperature. CO2 insensitivity occurred under the same conditions that resulted in O2 insensitivity. A complete loss of O2 sensitivity occurred up to 22.degree. C in Lycopersicon but only up to 6.degree. C in Scropularia. In Lycopersicon and Populus, O2 and CO2 insensitivity occurred under conditions regularly encountered during the cooler portions of the day. Because O2 insensitivity is an indicator of feedback limited photosynthesis, these results indicate that feedback limitations can play a role in determining the diurnal carbon gain in the field. At higher partial pressures of CO2 the temperature at which O2 insensitivity occurred was higher, indicating that feedback limitations in the field will become more important as the CO2 concentration in the atmosphere increases.