Abstract: By using Li6400 portable photosynthesis system, the photosynthetic parameters of winter wheat (Triticum aestivum) during its heading stage in North China Plain were measured at air temperature 25 ℃ and 30 ℃ and at photosynthetically available radiation 1500 and 2000 mmol·m^-2·s^-1. The measured data were fitted with the modified rectangular hyperbola models of the photosynthetic responses to flag leaf intercellular CO₂ concentration (A/C_i) and air CO₂ concentration (A/C_a), aimed to approach the reasonability of the fitted results obtained from the models. The photosynthetic capacity and CO₂ compensation point estimated by the modified A/C_i curve and A/C_a curve were nearly the same, but the photorespiration and initial carboxylation efficiency estimated by them were completely different. The difference between the two modified curves came from the calculated but not the real intercellular CO₂ concentration. Modified A/C_a curve was more reasonable than the modified A/C_i curve, because the potorespiration rate estimated by the former was close to the measured value.

Key words: LAI, Chlorophyll content, MODIS VI, Correlation analysis