1. College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, China
2. Key Laboratory of Plant Nutrition and the Agro-environment in Northwest China, Ministry of Agriculture, Yangling, Shaanxi 712100, China
3. School of Environmental Science and Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou 510006, China