1. Key Laboratory of Urban Agriculture (North China) Ministry of Agriculture and Rural Affairs of the People's Republic of China/College of Bioscience and Resource Environment Beijing University of Agriculture Beijing 102206 P. R.China
2. Beijing Key Laboratory of Detection and Control of Spoilage Microorganisms and Pesticide Residues in Agricultural Products Beijing University of Agriculture Beijing 102206 P. R. China
3. Agricultural Clean Watershed Research Group Institute of Environment and Sustainable Development in Agriculture Chinese Academy of Agricultural Sciences Beijing 100081 P. R. China