The classif ication of C3 and C4 plant functional types has become an important issue in global change research

but the mechanism of using remote sensing data remains unclear.In this paper

a diurnal variation experiment was designed for soybean（C3 plant functional type） and maize（C4 plant functional type） to acquire canopy spectra under different illumination and temperature conditions

and chlorophyll fluorescence（ChlF） signals and photochemical reflectance index（PRI） were extracted from the canopy spectra.The results showed that:（1） the amplitudes of the diurnal variation in ChlF between soybean and maize were signif icantly different

as the relative ChlF of soybean increased rapidly under heat and high irradiance stresses in the afternoon

but the increasing trend was not found in maize;（2） there was also an apparent increase in the ratio f688/f760of ChlF intensities of soybean in the afternoon

but this did not appear in maize;（3） the midday photosynthetic depression occurred in C3 crops owing to the stressed light and temperature

with a rapid increase in PRI.However

there was no apparent noon depression in C4 crops.Based on the different characteristics between the responses of C3 and C4 crops to high irradiance and temperature stressws

we proposed a potential method to discriminate C3 and C4 plants by multitemporal and hyper spectral remote sensing data.