title: Influence of rice straw amendment on mercury methylation and nitrification in paddy soils.
abstract: Currently, rice straw return in place of burning is becoming more intensive in China than observed previously. However, little is known on the effect of returned rice straw on mercury (Hg) methylation and microbial activity in contaminated paddy fields. Here, we conduct a microcosm experiment to evaluate the effect of rice straw amendment on the Hg methylation and potential nitrification in two paddy soils with distinct Hg levels. Our results show that amended rice straw enhanced Hg methylation for relatively high Hg content soil, but not for low Hg soil, spiking the same additional fresh Hg. methylmercury (MeHg) concentration was significantly correlated to the dissolved organic carbon (DOC) content and relative abundance of dominant microbes associated with Hg methylation. Similarly, amended rice straw was found to only enhance the potential nitrification rate in soil with relatively high Hg content. These findings provide evidence that amended rice straw differentially modulates Hg methylation and nitrification in Hg contaminated soils possibly resulting from different characteristics in the soil microbial community. This highlights that caution should be taken when returning rice straw to contaminated paddy fields, as this practice may increase the risk of more MeHg production.
  
  
  RESULTS
  Rice straw amendment enhanced both Hg methylation and nitrification potential in the relatively high, but not low, Hg soil.
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Electronic address: yrliu@rcees.ac.cn.
authors.forename: Yu-Rong
authors.initials: YR
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Ji-Xin
authors.initials: JX
authors.lastname: Dong
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Li-Li
authors.initials: LL
authors.lastname: Han
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Yuan-Ming
authors.initials: YM
authors.lastname: Zheng
authors.affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; Faculty of Veterinary and Agricultural Sciences, the University of Melbourne, Parkville 3010, Victoria, Australia.
authors.forename: Ji-Zheng
authors.initials: JZ
authors.lastname: He
mesh_terms: D000327:Adsorption; D002681:China; D004787:Environmental Pollution; D052918:Environmental Restoration and Remediation / Q000295:instrumentation / Q000379:methods*; D008745:Methylation; D008767:Methylmercury Compounds / Q000737:chemistry*; D058465:Nitrification; D012275:Oryza / Q000737:chemistry*; D018547:Plant Stems / Q000737:chemistry; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry*
chemical_list: D008767:Methylmercury Compounds; D012987:Soil; D012989:Soil Pollutants
keywords: Dissolved organic carbon; Environmental risk; Methylmercury; Microbial community; Nitrification