Author contributions statement
GQX and LST conceived this study; GQX. and JM designed the experiments;
XJM. performed the experiments and analyzed the samples; JM provided
technical support in the field; GQX and XJM. process the data. The
manuscript was composed by GQX with constructive suggestions and
carefully editing by LST; all the authors contributed to writing and
revising the manuscript.
Conflict of interest The authors declare that they have no
conflict of interest.