Analysis of Major Effecting Factors on Diurnal Changes of Photosynthetic Rate for Leaves of Alfalfa

During fine weather,daily changes in photosynthetic rate(Pn) and its effecting factors were determined by Portable LI-6400 Photosynthesis System under dry farming for alfalfa species at the flowering after the first cutting in the fourth growth year.The relationships between diurnal changes of photosynthetic rate(Pn) and its factors were analyzed with correlation analysis and path analysis.The result as follows.The curves of diurnal change in photosynthetic rate(Pn) of alfalfa leaves all had two peaks, and the first peak value appearing around ten o'clock was higher than the second around fourteen o'clock.In addition,there was an obvious midday around 12:00 o'clock.During 6:00-10:00 o'clock period,climbing of photosynthetic rate(Pn) was primarily caused by photosynthetic active radiation(PAR),leaf temperature(Ti),relative humid(RH).Descending photosynthetic rate(Pn) from 10:00 o'clock to 14:00 o'clock,especially middy depression was mostly caused by stomata factor.During 14:00-18:O0 o'clock,non-stomata factors were primary reason of descending of photosynthetic rate(Pn).