Acclimation of Photosynthesis to Temperature in Eight Cool and Warm Climate Herbaceous C(3) Species: Temperature Dependence of Parameters of a Biochemical Photosynthesis Model

To determine how parameters of a Farquhar-type photosynthesis model varied with measurement temperature and with growth temperature, eight cool and warm climate herbaceous crop and weed species were grown at 15 and 25 degrees C and single leaf carbon dioxide and water vapor exchange rates were measured over the range of 15 - 35 degrees C. Photosynthetic parameters examined were the initial slope of the response of assimilation rate (A) to substomatal carbon dioxide concentration (C(i)), A at high C(i), and stomatal conductance. The first two measurements allow calculation of V(Cmax), the maximum rate of carboxylation of ribulose bisphosphate carboxylase and J(max), the maximum rate of photosynthetic electron transport, of Farquhar-type photosynthesis models. In all species, stomatal conductance increased exponentially with temperature over the whole range of 15 - 35 degrees C, even when A decreased at high measurement temperature. There were larger increases in conductance over this temperature range in the warm climate species (4.3 x) than in the cool climate species (2.5 x). The initial slope of A vs. C(i) exhibited an optimum temperature which ranged from 20 to 30 degrees C. There was a larger increase in the optimum temperature of the initial slope at the warmer growth temperature in the cool climate species than in the warm climate species. The optimum temperature for A at high C(i) ranged from 25 to 30 degrees C among species, but changed little with growth temperature. The absolute values of both the initial slope of A vs. C(i) and A at high C(i) were increased about 10% by growth at the warmer temperature in the warm climate species, and decreased about 20% in the cool climate species. The ratio of J(max) - V(Cmax) normalized to 20 degrees C varied by more than a factor of 2 across species and growth temperatures, but differences in the temperature response of photosynthesis were more related to variation in the temperature dependencies of J(max) and V(Cmax) than to the ratio of their normalized values.