AUTHOR CONTRIBUTIONS
Z. Guo and S. Shi supervised the project. S. Shi, C. Zhong, X. Li, H. Lyu and N. C. Duke collected the samples. Z. Wang, H. Lyu and X. Li produced the data. Z. Wang and Z. Guo analyzed the data. Z. Guo and Z. Wang wrote the manuscript. S. Shi and N. C. Duke helped in improving the manuscript. All the authors read and approved the final manuscript.