AUTHOR CONTRIBUTIONS
Qingmin Pan, Hao Zhang, and Mengli Zhao conceived the ideas and designed the study. Mengli Zhao and Guodong Han designed the grazing experiment. Yang Yang and Hao Zhang conducted the field sampling and laboratory analysis. Yang Yang, Wei Liu, and Jiamei Sun analyzed the data. Yang Yang, Hao Zhang, and Qingmin Pan led writing of this manuscript. All authors contributed to the draft and revision and gave the final approval for publication.