Translocation of TiO2 nanoparticles enhances phosphorus uptake by wetland plants: Evidence from Pistia stratiotes and Alisma plantago-aquatica

Abstract

Titanium dioxide nanoparticles (nTiO₂) and phosphorus (P) are widely present in sewages. To verify the hypothesis and the associated mechanisms that root-to-shoot translocation of nTiO₂ can enhance plant P uptake thus P removal during sewage treatment, two wetland plants (Pistia stratiotes and Alisma plantago-aquatica) with different lateral root structures were used to examine the effect of nTiO₂ (89.7% anatase and 10.3% rutile) on plant growth and P uptake in a hydroponic system. Inductively coupled plasma-optical emission spectroscopy and transmission electron microscopy-energy dispersive spectroscopy showed that P. stratiotes with well-developed lateral roots translocated 1.4-16 fold higher nTiO₂ than A. plantago-aquatica with poorly developed roots, indicating P. stratiotes is efficient in nTiO₂ uptake. In addition, nTiO₂ root-to-shoot translocation in P. stratiotes increased with increasing nTiO₂ concentration, while the opposite occurred in A. plantago-aquatica. Corresponding to the stronger nTiO₂ translocation in P. stratiotes, its P uptake efficiency (I_max) and P accumulation were greater than that in A. plantago-aquatica, with I_max being increased by 35.8% and -16.4% and shoot P concentrations being increased by 16.2-64.6% and 11.4%, respectively. The strong positive correlation between Ti and P concentrations in plant tissues (r = 0.72-0.89, P < 0.01) indicated that nTiO₂ translocation enhanced P uptake. Moreover, nTiO₂-enhanced P uptake promoted plant growth and photosynthetic pigment synthesis. Therefore, wetland plants with well-developed lateral roots like P. stratiotes have potential to be used in P removal from nTiO₂-enriched sewages.

Keywords: P uptake; Physiological effects; TiO(2) nanoparticles; Translocation; Wetland plant.