Acknowledgements
This work was supported by the National Natural Science Foundation of
China (grant No. 31830015), the National Key Research and Development
Program of China (grant No. 2016YFA0600801) and the Strategic Priority
Research Program of the Chinese Academy of Sciences (grant No.
XDB15010301). We are grateful to Wei Zhang, Shunzhong Wang, Edith Bai,
Zongwei Xia, Jiabing Wu, Longchi Chen, Bing Fan and Qingui Wang for
their helps during collecting soil samples.