Cold acclimation inhibits CO2-dependent stimulation of photosynthesis in spring wheat and spring rye

We assessed the effects of short-term elevated CO2 on the light-saturated rates of photosynthesis (A(sat)) of spring ('SR4A', cKatepwa') and winter ('Musketeer', 'Norstar') wheat (Triticum aestivum L.) and rye (Secale cereale L.) cultivars grown at ambient CO2 (380 mu mol C.mol(-1)) at either 20/16 degrees C (nonacclimated, NA) or 5/5 degrees C (cold acclimated, CA). In spring wheat-rye, cold acclimation decreased CO2-stimulation of A(sat) by 45%-60% relative to NA controls following a short-term (80 h) shift of plants from ambient to elevated CO2 (700 mu mol C.mu mol(-1)). In contrast, in winter wheat-rye, cold acclimation enhanced CO2-stimulation of A(sat) by 15%-35% relative to NA controls upon a shift to elevated CO2. The stimulation observed for CA spring cultivars was about 60% less than that of CA winter cultivars. We conclude that a short-term exposure of spring cultivars to elevated CO2 cannot compensate for the cold acclimation-induced inhibition of A(sat). Cold acclimation of spring cultivars appeared to exacerbate Rubisco CO2 substrate limitations present under ambient CO2. Furthermore, CA spring cultivars were unable to adjust their short-term temperature sensitivity of A(sat) under elevated CO2 compared with the winter cultivars.