Effects of Full-Season Temperature Free-Air-Controlled Enhancement (T-FACE) Ecosystem Warming on Leaf Gas Exchange Properties and Water Relations of Spring Wheat.

Atmospheric CO₂ concentration is rising and it is predicted to cause global warming and to alter precipitation patterns, thereby affecting plant physiological processes.  Because variations in air temperature can significantly influence gas exchange properties and the internal water status of agronomic crops, our objective was to quantify the ecophysiological response of spring wheat (Triticum aestivum L. cv. Yecora Rojo) to any potential concomitant rise in ambient temperatures associated with Global Change.  Pursuant to this aim a T-FACE apparatus was implemented to facilitate full-season infrared-based ecosystem warming of a spring wheat canopy by 3 and 1.5 ^oC during the diurnal and nocturnal periods, respectively.  The experimental design was a completely randomized latin square (3x3) consisting of 3 ecosystem warming treatments (i.e., heaters, control, reference) replicated 3 times over 3 planting dates (i.e., January, March, September) during  2007 and 2008.  The net photosynthetic rates of wheat leaves were measured across a wide range of leaf temperatures and compared to those derived from a theoretical-based Arrhenius temperature response function.  Good agreement occurred between the actual- and theoretical-based results, thereby supporting the utility of the Arrhenius-based temperature response function to predict rates of reactions in crop growth models.  This exercise has increased our knowledge on how to improve models which are used to devise strategies to mitigate the adverse effects of global warming, whilst maximizing those that are beneficial.   Furthermore, our results have enabled more efficient use of our water resources, thereby helping to sustain cereal crop production in a future high-CO₂ world - especially, under dryland conditions.