Characteristics of Photosynthesis in Wheat Cultivars with Different Sensitivities to Ozone Under O 3-Free Air Concentration Enrichment Conditions

Abstract

With the help of the Chinese Ozone-Free Air Concentration Enrichment (O 3FACE) platform, the responses of photosynthsis characteristics to elevated O 3 concentration were investigated using winter wheat ( Tritcium aestivum L.) cultivars Yannong 19 and Yangmai 16, which differ in sensitivities to O 3. Under O 3 treatment for 75 d, the net photosynthetic rate ( P n), stomtal conductance ( G s), and transpiration rate ( T r) decreased significantly in both cultivars, whereas the intercellular CO 2 concentration ( C i) changed slightly. The O 3-sensitive cultivar Yannong 19 had larger reductions in P n (61.1%), G s (68.0%), and T r (57.4%) than Yangmai 16 (27.9%, 37.5%, and 27.9%, respectively). This indicated that the reduction of P n mostly resulted from the nonstomatal factors in cooperation with stomal factors. In the chlorophyll fluorescence parameters, the maximal photochemical efficiency of PSII in the dark ( F v/ F m), the potential activity of PSII ( F v/ F o), the photochemical quenching ( q P), and the rate of photochemical reaction ( P rate) decreased in the O 3 treatment, but the nonphotochemical quenching (NPQ) and the rate of thermal dissipation ( D rate) showed a upward tendency. The change tendency of total soluble protein content and the amount of Rubisco was similar to that of chlorophyll fluorescence parameters and P n. The results implied that the major nonstomal factors responsible for the P n decrease under elevated O 3 concentration were the Ribulose-1,5-bisphosphate (RuBP) carboxylation limitation and the damage of PSII. The change extents of all the parameters were larger in Yannong 19 than in Yangmai 16. The high T r value and slow reduction of Rubisco amount in Yangmai 16 are probably crucial reasons for its high photosynthetic rate.