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 wa rm 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 measu red over the range of 15 - 35 degrees C. Photosynthetic parameters examined were the initial slope of the response of assimilation rate (A) to substom atal carbon dioxide concentration (C-i), A at high C-i, and stomatal conduc tance. 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 photosy nthesis models. In all species, stomatal conductance increased exponentiall y with temperature over the whole range of 15 - 35 degrees C, even when A d ecreased at high measurement temperature. There were larger increases in co nductance over this temperature range in the warm climate species (4.3 x) t han in the cool climate species (2.5 x). The initial slope of A vs. C-i exh ibited an optimum temperature which ranged from 20 to 30 degrees C. There w as 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 cli mate species. The optimum temperature for A at high C-i ranged from 25 to 3 0 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 we re increased about 10% by growth at the warmer temperature in the warm clim ate 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 temper ature response of photosynthesis were more related to variation in the temp erature dependencies of J(max) and V-Cmax than to the ratio of their normal ized values.