Geographic background of East Central Asia and division of the sampling transect.

<p>A–northern slope of the Qinling Mountains, central China; B–Loess Plateau, north China, which is dichotomy between the south (B₁) and north (B₂); C—central and east Ningxia Autonomous Region and southwest edge of the Mu Us sandy land, north China; D—northwest Ordos plateau, Yellow River valley and the southern slope of Yinshan mountains, north China; E—northern slope of the Yinshan Mountains, north China; F—Gobi desert in north China and south Mongolia; G—north Mongolia. The dots, circles, squares and triangles in various colors in the transect indicate the sampling sites. Insert above: study area in the Eurasia continent, the white arrows indicate the advancing directions of maritime air-masses; Insert below: elevation changes in the transect in meters above sea level (a.s.l.).