Elevated CO2 accelerates polycyclic aromatic hydrocarbon accumulation in a paddy soil grown with rice.

The concentration of atmospheric carbon dioxide (CO2) and polycyclic aromatic hydrocarbons (PAHs) contents in the environment have been rising due to human activities. Elevated CO2 (eCO2) levels have been shown to affect plant physiology and soil microbes, which may alter the degradation of organic pollutants. Here, we study the effect of eCO2 on PAH accumulation in a paddy soil grown with rice. We collected soil and plant samples after rice harvest from a free-air CO2 enrichment (FACE) system, which had already run for more than 15 years. Our results show that eCO2 increased PAH concentrations in the soil, and we link this effect to a shift in soil microbial community structure and function. Elevated CO2 changed the composition of soil microbial communities, especially by reducing the abundance of some microbial groups driving PAH degradation. Our study indicates that elevated CO2 levels may weaken the self-cleaning ability of soils related to organic pollutants. Such changes in the function of soil microbial communities may threaten the quality of crops, with unknown implications for food safety and human health in future climate scenarios