Analysis of Photosynthesis Efficiency of Maize Hybrids with Different Yield in the Later Growth Stage

The photosynthetic efficiency of maize hybrids with different yield in the later growth stage was investigated through measurements of photosynthetic rate and chlorophyll fluorescence parameters of photosystem Ⅱ using a portable CIRAS 1 photosynthetic gas analysis system and portable fluorescence monitoring system (FMS2). In the field condition, photon flux density(PFD) had greater influence on net photosynthetic rate (P n) than CO 2 concentration (C a) in two hybrids, and there existed difference between the response of P n to PFD and C a in the same hybrid. The declines in maximal photochemical efficiency of PSⅡ in the darkness(Fv/Fm), actual photochemical efficiency of PSⅡ in the light (ΦPSⅡ) and photochemical quenching co efficient(qP) were observed at midday strong sunlight. The 3 indexes in the milky stage were higher than that in the doughy stage. On the other hand, photosynthetic rate (P n) and non photochemical quenching (NPQ) amounted to maximum value at midday. The value of NPQ in the doughy was higher than that in the milky. All the 5 indexes showed different between two hybrids. Higher yield hybrid YY23 had higher Fv/Fm, ΦPSⅡ, qP, P n and lower NPQ when compared with lower yield hybrid YY5. The difference of those parameters at midday was especially obvious, and larger difference displayed in the doughy than in the milky stage.