* Corresponding authors

^a Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China
E-mail: fxh73@mail.hzau.edu.cn
Fax: +86 27 87288618
Tel: +86 27 87280271

^b Department of Ecosystem Science and Management, University of Wyoming, Laramie, WY, USA

^c Physical Chemistry and Soft Matter, Wageningen University, Dreijenplein 6, 6703 HB Wageningen, Netherlands

^d Key Laboratory of Surficial Geochemistry, Ministry of Education, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China

^e Department of Chemistry, Brookhaven National Lab, Upton, New York 11973, USA

^f Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039, China

^g State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

^h Function Laboratory for Marine Geology, National Oceanography Laboratory, Qingdao 266061, China

ⁱ Environmental Soil Chemistry Group, Delaware Environmental Institute and Department of Plant and Soil Sciences, University of Delaware, Newark, Delaware, USA