Suppression of photorespiration by low O2 concentrations (Method 1) and simultaneous measurements of gas exchange and chlorophyll fluorescence (Method 2) are often used to estimate leaf photorespiration rate (Rp) of C3 plants. However, it is largely unknown whether Method 1 and Method 2 can be used equivalently in estimating Rp. Using a field experiment on two wheat cultivars (T. aestivum JM22 and T. aestivum Z39-118) whose leaf gas exchange and chlorophyll fluorescence at low and normal O2 concentrations (2% versus 21% O2) were simultaneously measured across a wide range of light intensities (I), this study assessed the impacts of the two measures on Rp and its response under changing irradiance conditions. All the above quantities increased with the increasing I until reaching the cultivar-specific maximum values and the corresponding saturation light intensities. However, there were significant differences between Rp estimated by Method 1 and Method 2 at the I range from 150 to 2000 μmol m-2 s-1 for T. aestivum JM22 and from 150 to 1000 μmol m-2 s-1 for T. aestivum Z39-118. These findings demonstrated that the two methods cannot be used equivalently under changing irradiance conditions.
Keywords: Electron flow; Light response; Photoprotection; Photorespiration; Photosynthesis; Saturation light intensity.
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