Acclimatory responses of stomatal conductance and photosynthesis to elevated CO2 and temperature in wheat crops grown at varying levels of N supply, in a Mediterranean environment

The short and long-term responses of flag leaf stomatal conductance (gs) and rate of photosynthesis (An) to elevated CO2 (757 μmol mol), 4 oC warmer temperatures and N supply were investigated in spring wheat (Triticum aestivum L. cv. Alcalá) crops grown in two seasons in field conditions under temperature gradient tunnels, in a Mediterranean environment. Plants grown at elevated CO2 had lower gs and An measured at 700 μmol mol CO2 than ambient CO2-grown plants, indicating acclimatory responses to elevated CO2. N supply, which was lower in 2003 than 2002, reduced this acclimation in both years. Warmer temperatures at high nitrogen supply also decreased An acclimation. Acclimatory responses of An and gs were highly correlated. The analysis of the gs – An relationship indicated that both parameters are probably linked and respond in parallel to elevated CO2 at ambient temperatures, but non-parallel responses were observed at above-ambient temperatures. Abbreviations: An, net photosynthesis rate; Ca, atmospheric CO2 concentration; Ci, CO2 concentration in the intercellular air space of leaves; gs, leaf stomatal conductance; Hr, air relative humidity; PFD, photosynthetic flux density; Rubisco, Ribulose, 1-5, bisphosphate carboxylase oxygenase. Key-words: acclimation, elevated CO2, elevated temperature, gas exchange, nitrogen, photosynthetic capacity, stomatal conductance.