The study region is located in the southeast to northwest (~400 km) hilly transect of loess plateau in northern Shaanxi province of China (107°39′-109°15′E, 34°4′-37°31′N, altitude: 415–1,633 m a.s.l.). The region is characterized by semi-arid continental climate with an average annual rainfall of 513 mm. The mean annual air temperature is ~8.8°C. Soils in the study area are mainly derived from loess, according to the soil classification system of the Food and Agriculture Organization of the United Nations (FAO) and further classified as Calcic Cambisols (IUSS Working group WRB, 2014 (link)) with silty loam texture. A transitional environment from south to north is represented by forest, forest-grassland, and grassland to dessert grassland vegetation belts. Qingling (QL) and Ziwuling (ZWL) represent locations of mountain forests; Liandaowan (LDW) represents sites from grassland township; Guanzhong (GZ), Luanchuan (LC) and Weibei (WB) refer to agricultural areas from three Loess tablelands, respectively (Figure S1 ); while Ansai county (AS) and Jingbian county (JB) from regions of forest steppes (Figure S1 ). The codes of A, B and C following the above-mentioned site abbreviations represent various biological replicates at landscape scales. The geographical and typical vegetation characteristics of the investigated sites are as given in Table 1 . In each site, three replicate subplots were randomly selected with an area of 15 m × 15 m and six replicate soil subsamples were collected from each subplot and at the soil depths of 0–10 cm using auger boring with a drill size of 20 cm length and 2 cm diameter. 6 subsamples of identical soil depths were sieved through a 2 mm mesh and then mixed to form a composite sample of ~100 g. A 10 g subsample from each plot was immediately wrapped in aluminum foil, quenched with liquid N2, and stored at −80°C laboratory conditions until the extraction of soil DNA.
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