Effect of Pb stress on growth and photosynthetic characteristics in Rehmannia glutinosa
To clarify the effects of lead(Pb)stress on the growth and photosynthetic characteristics of Rehmannia glutinosa,and to explore the response mechanism of medicinal plants to heavy metal stress,a pot experiment was conducted using'Beijing No.3'as the experimental material to investigate growth mass leaf photosynthetic pigment content,photosynthetic parameters and chlorophyll fluorescence parameters as influenced by five exogenous Pb concentration(50,100,200,300,400 mg·kg-1).Soil without added Pb was used as the control(0 mg·kg-1).The results showed that high concentration of Pb treatment inhibited the growth of leaf number,leaf length,leaf width and leaf thickness of R.glutinosa.The photosynthetic pigment content and chlorophyll fluorescence parameters increased first and then decreased with the increase of Pb concentration during the whole growth period.Electron transport rate,photosynthetic quantum yield,maximum fluorescence and initial fluorescence were significantly decreased.With the increase of Pb concentration,the net photosynthetic rate,stomatal conductance and intercellular CO2 concentration of R.glutinosa leaves gradually decreased from the initial stage of R.glutinosa expansion to the early stage of R.glutinosa expansion,and increased first and then decreased from the middle stage to the harvest stage.The transpiration rate decreased with the increase of Pb concentration during the whole growth period.The tolerance of photosynthetic characteristics of R.glutinosa to Pb was 50 mg·kg-1 treatment＞100 mg·kg-1 treatment＞0 mg·kg-1 treatment＞200 mg·kg-1 treatment＞300 mg·kg-1 treatment＞400 mg·kg-1 treatment.This study compared the effects of different Pb concentrations on the growth and photosynthetic characteristics of R.glutinosa in different growth stages,and analyzed the resistance mechanism of R.glutinosa to Pb,in order to provide an important technical reference for the safe use of farmland soil and the planting management of R.glutinosa.
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