Phosphate Absorption Mechanism of plants’ Phosphorus Absorption Membrane Transport protein Ion channel Carrier Diffusion Active transport Ion channel Ion channel Ion channel Carrier Ion channel Carrier Ion channel Carrier Carrier Ion channel Carrier Membrane Transport protein Carrier Membrane Transport protein Ion channel Carrier Membrane Transport protein M O I H + -ATPase H + ATP+H 2 O ADP+Pi OH - + ADP H 2 O Phosphate Carrier OH - H 2 PO 4 - HPO 4 2- PO 4 3 - H 2 PO 4 - Ion channel Carrier Membrane Transport protein
Advantages of Duckweed for Phosphorus-Containing Wastewater Treatment Strong Phosphorus Absorptive Capacity; Fast Growth Rate; Easy for Reaping; High Protein Animal Feed; No Secondary Pollution.
In Vitro Experiment Factors affecting Pi uptake rate : Genotype ； Photon flux density ； Temperature ； pH; Phosphorus concentration.
Tab.1 Phosphorus absorbency comparison of different duckweed genotypes The English capital letter and lowercase expressed the mean difference is significant at the .01 and .05 level in the treats. Genotypes Biomass increase （ g ） Total Pi uptake （ mg ） Pi uptake rate (mgPi/gFW) L. aequinoctialis 3.197±0.327aA 3.382±0.010aA 1.066±0.112aA S. oligorrhiza 1.684±0.037bB 3.312±0.003bB 1.967±0.045bB S. polyrrhiza 1.663±0.063bB 3.336±0.005cC 2.008±0.077bB
Fig.1 The relationship between pi uptake rate and its concentration in solution （ a: L. aequinoctialis ， b: S. oligorrhiza ， c: S. polyrrhiza ） a b c
Tab.2 Kinetic parameters of Pi uptake by different genotypes of duckweed **: the siginificant were at 1% level. Genotypes Kinetic Equation R 2 K m (μmol/L) V max (μmol/gFW•hr) L. aequinoctialis S. oligorrhiza S. polyrrhiza I=5C/ (1.25+C) I=7.698C/ (2.186+C) I=9.606C/ (2.695+C) 0.971 ** 0.966** 0.987** 1.250 2.186 2.695 5.000 7.698 9.606
Fig. 2 Ultrastructure of chloroplasts in mesophyllic cells of different duckweed genotypes a b c （ a: L. aequinoctialis×18500 ， b: S. oligorrhiza ×26500 ， c: S. polyrrhiza ×26500 ）
Fig. 3 ACP activities of different duckweed genotypes
Spriodela had a higher phosphorus uptake capacity, though it’s growth rate was lower than the Lemna; Phosphorus uptake kinetics in duckweed were in accord with the Michaelis-Menten equation; Conclusions
The K m value for Pi uptake of Lemna aequinoctialis was less than that of Spirodela oligorrhiza and Spriodela polyrrhiza, making it a better candidate for treating wastewater with a lower Pi concentration ； The V m value of phosphorus uptake by Spriodela polyrrhiza was higher than that of the other two genotypes , which might lead to a better performance of Spriodela polyrrhiza in purifying wastewater with a higher Pi concentration; Conclusions
Compared with Lemna, leaf chloroplast morphology of Spriodela promoted the export of assimilation products; ACP activity of Spriodela was higher than that of Lemna, which also indicated Spriodela may have a higher phosphorus uptake capacity. Conclusions