Aims Ozone is a prominent gas pollutant that adversely affects vegetation, including visible leaf injury, growth and yield reduction. Our objective was to assess photosynthesis, growth and yield responses of field-grown wheat to increased ozone.
Methods We planted winter wheat (Triticum aestivum cv. Jia 403) in 12 plots of 2 m×2 m on 7 November 2005. After the wheat greened, we established 12 open-top octagonal (2.2 m high, 2 m diameter) chambers on 1 March 2006. Except rainy days, wheat was exposed to charcoal-filtered air, unfiltered air, and two treatments with ozone addition (DO100, DO150) from 13 March to 28 April 2006, for 8 h per day, for a total of 30 days. We measured diurnal gas exchange and P_n-PAR response curves of flag leaves at the early grain filling stage (after 25 days exposure to ozone) and components of yield at harvest.
Important findings High concentration of ozone altered gas exchange parameters, including stomatal conductance (G_s), leaf photosynthetic rate (P_n), transpiration rate (T_r) and intercellular CO₂ concentration (C_i). Apparent quantum yield (AQY), light saturation point (LSP) and light compensation point (LCP) were significantly decreased, suggesting photosynthetic capacity could also be changed, characterized as reduced photon-saturated photosynthetic rate (P_max). The decrease of photosynthetic activity was probably dominated by non-stomatal factors in combination with stomatal closure. In addition, ozone exposure caused leaf aging and decreases in plant height, ear length and number of grains per ear. Although similar responses were observed in plants exposed to ambient ozone concentration, we found no statistically significant differences at current concentration. We concluded that dynamic ozone exposure detrimentally affects photosynthesis, growth and yield of winter wheat.