ACKNOWLEDGEMENTS
This study was jointly financed by the State Key and General Programs of National Natural Science Foundation of China (Nos. 41571130043, 41571251). This study was conducted at the Puding Karst Ecosystem Station of Chinese Academy of Sciences. We thank the field station staff for their assistance with sampling. We thank Professor David Powlson of Rothamsted Research, UK, for helpful scientific discussion and for improving the English language of this paper.