Table I.

Key parameters involved in the calculation of photorespiratory rates for wild-type oilseed rape measured at different leaf temperatures

ParameterLeaf Temperature
15°C20°C25°C
CO2compensation point when oxygenation equals carboxylation  (Γ*, μmol mol−1)28.3 ± 1.1a 41.1 ± 2.9b 40.8 ± 0.3b
Non-photorespiratory respiration (Rd, μmol m−2s−1)0.65 ± 0.12a 0.91 ± 0.17b 1.42 ± 0.28c
Photosynthesis (A, μmol m−2s−1)* 5.26 ± 0.21a 8.08 ± 1.20b 11.84 ± 1.70b
Transpiration (E, mmol m−2s−1)* 2.04 ± 0.34a 2.97 ± 0.12b 4.50 ± 0.10c
Leaf conductance (g, mmol m−2s−1)* 78.4 ± 13.3a 70.2 ± 3.0a 79.3 ± 1.6a
Intercellular CO2 concentration (Ci, μmol mol−1)* 283.1 ± 8.8a 232.7 ± 12.2b 195.4 ± 18.3c
Specificity factor (oxygenation/carboxylation; Φ, dimensionless)0.20 ± 0.01a 0.31 ± 0.03b 0.42 ± 0.04b
Photorespiration*o/2, μmol m−2s−1)0.66 ± 0.05a 1.65 ± 0.46a 3.52 ± 0.75b
Photorespiration relative to photosynthesis12.5%20.4%29.7%

Parameters marked with an asterisk were obtained at a PPFD of 400 μmol m−2 s−1. Errors represent ±se. Values marked with the same letter are not significantly different (P > 0.05).