Photosynthetic Characteristics of Six Brassica campestris ssp.chinensis Varieties

The photosynthetic characteristics of six Brassica campestris ssp.chinensis varieties were studied and the results indicated that at the light intensity of 800 μmol·m~ -2 ·s~ -1 ,‘Zhengda kangre qing No.3’ had the highest net photosynthetic rate,which amounted to 16.37 μmol CO_2·m~ -2 ·s~ -1 ,and its apparent quantum yield,carboxylation efficiency and water use efficiency were the highest amounting to 0.044 2, 0.085 4 mol·m~ -2 ·s~ -1 and 6.20 μmol CO_2·mmol~ -1 H_2O;‘Luxing’ had the lowest dark respiration rate,which amounted to 2.24 μmol CO_2·m~ -2 ·s~ -1 .Pn-PFD curves indicated that where the light intensity was below 300 μmol·m~ -2 ·s~ -1 ,the varieties slightly differed in net photosynthetic rate and where the light intensity changed from 300 μmol·m~ -2 ·s~ -1 to 1 000 μmol·m~ -2 ·s~ -1 they quickly increased their net photosynthetic rates.‘Zhengda kangre qing No.3’ had the highest light saturation point amounting to 1 910.3 μmol·m~ -2 ·s~ -1 and its net photosynthetic rate was the highest reaching 20.2 μmol CO_2·m~ -2 ·s~ -1 at the light saturation point;The varieties showed similar daily net photosynthetic rate patterns which,no matter the photosynthetic rate was high or low,were a double peak curve that indicated remarkable midday depression.