The Effects Of Carbon Nanotubes On Respiration And Photosynthesis

With the wide applications of carbon nanotubes(CNTs) in various fields such us medicine,electronics,military operations and so on,the security problem has aroused close attention from all sectors of society.Photosynthesis and respiration of plants are two important physiological processes in the transformation of matter and energy,which are the basis of the survival of animals, plants and human beings.It is significant to study the effect of CNTs on photosynthesis and respiration in plants,and to evaluate the toxic effects and environmental risks.In this thesis,dissolved oxygen electrode was used to measure the respiration and photosynthetic rate of aloe vera and pteris vittata processed with different diameters and concentrations of multi-walled carbon nanotubes(MWCNTs) to study the impact of MWCNTs on plant photosynthesis and respiration.MWCNTs was purified before using,and no catalyst residue was found in XRD test. The different concentrations of MWCNTs suspensions were obtained by ultrasonic dispersion of MWCNTs in culture medium or pure water. Healthy aloe vera leaves,with the aloe vera gel removed,were cut into2 mm x 3 mm slices and then divided into four parts of equal mass.Three of them was treated with different MWCNTs suspensions, respectively, the remaining one was used as control. Both the experimental and the control were cultured in the same condition for 12 hours. For pteris vittata, select four pieces of pteris vittata of the same length,three of them were cultured in the pure water suspension of 20 mg/L MWCNTs for 24,48 and 72 hours, respectively. The remaining one was cultured in pure water as the control.After cultivation, pteris vittata was washed with pure water and transferred into BOD bottle.The dissolved oxygen concentration in the BOD bottle was measured every 30 min.For respiration,compared with the control,10 mg / L,40 mg / L and 90 mg / L MWCNTs-1(20 nm-30 nm in diameter) showed different degrees of promotion. MWCNTs-5(<8nmin diameter) with concentrations of 10 mg/L and 40 mg/L has a certain inhibitory effecton the respiration of Aloe Vera,when the concentration reached 90 mg/L, the effect is not obvious.Within the first 48 hours, the inhibitory effect of MWCNTs-1 on respiration increased with the increase of treatment time, but decreased for 72 hours treatment. The respiration of pteris vittata was inhibited when processd with MWCNTs-5 for 12 hours.When the processing time increased to 48 h, however, the respiration was promoted.When the processing time reached 72 hours, the respiration of pteris vittata was again significantly inhibited.For photosynthesis,MWCNTs-1 of 10mg/L and 40mg/L promoted the photosynthesis of aloe vera. When the concentration reached 90 mg/L, inhibitory effect was observed. MWCNTs-5 of 10 mg/L and 90 mg/L also promoted the photosynthesis of aloe vera.But when the concentration of MWCNTs-5 was 40 mg/L, the effect on photosynthesis was not significant.Within the first 48 hours, MWCNTs-1 promoted the photosynthesis of pteris vittata. When the treatment time reached 72 h, this promoting effect was weakened. For MWCNTs-5, 24 hours of treatment promoted the photosynthesis of pteris vittata, while 48 hours treatment inhibited the photosynthesis, but 72 hours treatment again inibitated the photosynthesis.All the above results showed that both the photosynthesis and respiration process of plants can be affected by MWCNTS, but the dependences of the effect of MWCNTs onthe Morphology, concentration and treatment time are very complex, no simple progressive increasing or decreasing was observed. The mechanism behind this complexity still needs further research.