Elevated CO2 exacerbates effects of TiO2 nanoparticles on rice (Oryza sativa L.) leaf transcriptome and soil bacteria

Elevated CO2 affects the plant rhizosphere and can therefore affect the fate and toxicity of soil contaminants. However, little is known about how the effects of nanoparticles on plants and soil bacteria will change under future CO2 levels. A free-air CO2 enrichment system with two CO2 levels (ambient, 390 mu mol mol-1; elevated, 590 mu mol mol-1) was used to investigate the responses of rice (Oryza sativa L.) and soil bacteria to titanium dioxide nanoparticles (nano-TiO2, 0 and 200 mg kg-1). Results showed that nano-TiO2 alone did not significantly affect rice growth but affected soil bac-teria involved in the carbon and sulfur cycles. Elevated CO2 alone increased rice plant biomass and up-regulated genes related to ribosomes, but its combination with nano-TiO2 down-regulated genes related to photosynthesis and photo-synthetic antennae. Elevated CO2 also exacerbated the disturbance by nano-TiO2 to soil bacteria involved in carbon and nitrogen cycles, and consequently inhibited the rice growth. These findings provide a reference for the comprehen-sive evaluation for the risk of soil pollution.