Submitted to: Photosynthesis Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 19, 1999
Publication Date: N/A
Interpretive Summary: Predictions of crop growth under the global change conditions of increased atmospheric carbon dioxide and increased temperature rely on accurate predictions of photosynthesis. A widely used model of photosynthesis incorporates temperature dependencies which are based on very limited data. The purpose of these experiments was to determine how much the temperature dependencies of parameters of the photosynthesis model vary among species adapted to different warm and cool climates, and how much the temperature dependencies vary with prior exposure to different temperatures. The results indicated that there was substantial variation in the temperature dependencies of the photosynthetic parameters. Plants adapted to cool and warm conditions differed systematically, and also differed consistently in their response to growth at different temperatures. These results will increase the accuracy of models of photosynthesis for use in predicting effects of global change on crops, and will be of use to crop physiologist and the modelling community.
Technical Abstract: To determine how parameters of a Farquhar-type photosynthesis model varied with measurement temperature and with growth temperature, several cool and warm climate herbaceous crop and weed species were grown at 15 and 25 C and single leaf carbon dioxide and water vapor exchange rates were measured over the range of 15 to 35 C. Photosynthetic parameters examined were the initial slope of the response of assimilation rate to substomatal carbon dioxide concentration, assimilation rate at high carbon dioxide, and stomatal conductance. In all species, stomatal conductance increased exponentially with temperature over the whole range of 15 to 35 C, even when assimilation rate 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 exhibited an optimum temperature which ranged from 20 to 30 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 assimilation rate at high carbon dioxide ranged from 25 to 30 C among species, but changed little with growth temperature. The absolute values of both the initial slope and assimilation rate at high carbon dioxide were increased by growth at the warmer temperature in the warm climate species, and decreased in the cool climate species.