Photosynthetic Traits in Wheat Grown under Decreased and Increased CO2 Concentration, and after Transfer to Natural CO2 concentration

Wheat plants were grown from sowing to day 18 in 26-dm3 chambers at three different CO2 concentrations: 150 (-CO2), 350 (C, control), 800 (+CO2) μmol mol-1. Afterwards, plants of the three variants were grown at the same natural CO2 concentration. Plant characteristics were measured just before the transfer (0 days after CO2 treatment, DAT), and at 5 - 8 DAT on the 1st leaf, and at 12 - 22 DAT on the 4th leaf. Decreased or increased CO2 concentrations caused acclimations which persisted after transplantation to natural CO2 concentration. At 5 - 8 DAT, stomatal density, stomatal conductance (gs), CO2 saturated net photosynthetic rate (PNsat0), radiation saturated net photosynthetic rate (PNsat1), and carboxylation efficiency (τ) were higher in -CO2 plants and lower in +CO2 plants than in C plants. As compared with C plants, the photochemical efficiency (α) was lower in -CO2 and higher in -CO2 plants, however, chlorophyll (Chl) a, Chl b, Chl a-b and carotenoid contents were lower in both -CO2 and +CO2 plants. On the 4th leaf, which emerged on plant after finishing CO2 treatments, at 12 - 22 DAT, no differences in stomatal density and g, between treatments were observed. In -CO2 plants, pigment content and PNsat0 were higher, α was lower, and PNsat1 and τ were not different from C plants. In contrast, in +CO2 plants, pigment content, PNsat1 and τ were lower, and PNsat0 and α were unchanged. Leaf area, dry mass, and tiller development increased in +CO2 plants and decreased in -CO2 plants. In the interval between 8 and 22 DAT, lower net assimilation rate in +CO2 than in -CO2 plants was observed.