Figure 1

Sampling locations and climate conditions across China. Map A shows locations of 58 soil samples (orange) collected by Wang²⁷ and Xiao²⁹ from northeast China (group IV), 102 soil samples (green) collected by Wang²⁷ and Xiao²⁹ from northern China (group V), 42 soil samples (blue) collected by Ding³⁰ and Xiao²⁹ from Qinghai-Tibetan Plateau of China (group IV), 52 soil samples (purple) collected by Yang³² and lei³¹ from central China (group III), 13 soil samples (dark red) collected by Lei³¹ from Yunnan Plateau, southwest China (group II), and 47 soil and bog samples (bright red) collected by this study from southern China (group I). Map B illustrates spatial variations of mean annual temperature (C°) measured between 1971 and 2000. (C) Map C denotes the spatial variations of mean annual precipitation (mm) measured between 1971 and 2000. The MAP A was produced using ArcGIS, version number 10.5, http://esrichina.hk/ (The HKU has purchased the copyright of ArcGIS 10.5. The satellite imagery in map A were obtained from Google Earth, version number 7.3.1.4507, https://www.google.com/earth/download/gep/agree.html). Map data: Google, DigitalGlobe. The MAT and MAP data sets are provided by the Data Center for Resources and Environmental Sciences, Chinese Academy of Sciences (http://www.resdc.cn MAT: http://www.resdc.cn/data.aspx?DATAID=154 MAP: http://www.resdc.cn/data.aspx?DATAID=153).