Effect of elevated CO2 concentration on photosynthesis and flowering in three wheat species belonging to different ploidies

Diploid, tetraploid and hexaploid species of wheat were grown at ambient (375 μl l−1) or elevated (550 μl l−1) CO2 concentration [CO2] in a mid Free-Air CO2 Enrichment (FACE) facility, to study their differential response to CO2 enrichment. It was observed that elevated [CO2] consistently reduced the activity of Photosystem I (PS I) and PS II in all three wheat species investigated. Down regulation of photosynthesis may be attributed to feed back inhibition due to significantly higher accumulation of starch and total soluble sugars in grains and leaves. In spite of photosynthetic acclimation, dry weight of plants at harvest significantly increased in all the three species. CO2 enrichment also delayed the date of ear emergence and anthesis. Highest reduction in activity of PS I, and maximum accumulation of carbohydrates along with increase in biomass, was observed in Triticum dicoccoides. Maximum delay in ear emergence and anthesis was also observed in this species. Minimum reduction in the activity of PS I and PS II, and least increase in biomass, were observed in T. aestivum. The study reports, for the first time, a correlation between the altered carbohydrate composition and activity of the two photosystems and flowering time in wild and cultivated species of wheat grown in FACE facility.