Elevated CO and soil mercury stress affect photosynthetic characteristics and mercury accumulation of rice.

This is a novel study about responses of leaf photosynthetic traits and plant mercury (Hg) accumulation of rice grown in Hg polluted soils to elevated CO (ECO). The aim of this study was to provide basic information on the acclimation capacity of photosynthesis and Hg accumulation in rice grown in Hg polluted soil under ECO at day, night, and full day. For this purpose, we analyzed leaf photosynthetic traits of rice at flowering and grain filling. In addition, chlorophyll content, soluble sugar and Malondialdehyde (MDA) of rice leaves were measured at flowering. Seed yield, ear number, grain number per ear, 1000-grain weight, total mercury (THg) and methylmercury (MeHg) contents were determined after harvest. Our results showed that Hg polluted soil and ECO had no significant effect on leaf chlorophyll content and leaf mass per area (LMA) in rice. The contents of soluble sugar and MDA in leaves increased significantly under ECO. Mercury polluted soil treatment significantly reduced the light saturated CO assimilation rate (A) of rice leaves only at flowering, but not at grain filling. Night ECO greatly improved rice leaf water use efficiency (WUE). ECO greatly increased seed yield and ear number. In addition, ECO did not affect THg accumulation in rice organs, but ECO and Hg treatment had a significant interaction on MeHg in seeds, husks and roots.