The diurnal variation of leaf photosynthesis of alfalfa Gongnong No.1

Diurnal variations of leaf photosynthesis of alfalfa Gongnong No.1 were studied by Licor-6400 portable photosynthetic system in Beijing under natural condition.The results showed that the curve of diurnal variation in net photosynthetic rate(Pn) of the alfalfa leaves was dual-peaked with obvious midday depression of the photosynthesis efficiency.The diurnal variation trend of transpiration rate(E) was similar with that of Pn and the diurnal variation of internal cellular CO2 concentration(Ci) was just opposite to that of Pn.The diurnal variation between stomata conductance(Gs) and Pn were similar but not synchronism and their maximums appeared at the same time,the minimum of Gs was 2 hours later than Pn.Based on the analysis it was concluded that the midday depression of photosynthetic efficiency was mainly influenced by the non-stomatal limited factors.