Titanium dioxide nanoparticle(nano-TiO2),as an excellent UV absorbent and photo-catalyst,has been widely applied in modern industry,thus inevitably discharged into environment.We proposed that nano-TiO2 in soil can promote crop yield through photosynthetic and metabolic disturbance,therefore,we investigated the effects of nano-TiO2 exposure on related physiologic-biochemical properties of rice(Oryza sativa L.).Results showed that rice biomass was increased ＞30％at every applied dosage(0.1-100 mg/L)of nano-TiO2.The actual photosynthetic rate(Y(Ⅱ))significantly increased by 10.0％and 17.2％in the treatments of 10 and 100 mg/L respectively,indicating an increased energy production from photosynthesis.Besides,non-photochemical quenching(Y(NPQ))significantly decreased by 19.8％-26.0％of the control in all treatments respectively,representing a decline in heat dissipation.Detailed metabolism fingerprinting further revealed that a fortified transformation of monosaccharides(D-fructose,D-galactose,and D-talose)to disaccharides(D-cellobiose,and D-lactose)was accompanied with a weakened citric acid cycle,confirming the decrease of energy consumption in metabolism.All these results elucidated that nano-TiO2 promoted rice growth through the upregulation of energy storage in photosynthesis and the downregulation of energy consumption in metabolism.This study provides a mechanistic understanding of the stress-response hormesis of rice after exposure to nano-TiO2,and provides worthy information on the potential application and risk of nanomaterials in agricultural production.