Fig. 3: Geographical distributions and latitudinal variations of soil N-source contributions to terrestrial plants.

ƒNO3- (a, b), ƒNH4+ (c, d), and ƒEON (e, f) are fractional contributions of soil NO3-, NH4+, and EON to PUN, respectively. In panels (a), (c), and (e), gray areas are deserts, glaciers, perennial snow-covered areas, bare ground, and agricultural land etc. The mapping was conducted by ArcGIS version 10.8 (Esri Inc., USA) using the Kriging spatial interpolations based on the 0.1° (latitude) × 0.1° (longitude) grid-based data. The base map was downloaded from https://hub.arcgis.com/datasets/esri::world-countries-generalized. In panels (b), (d), and (f), red lines and gray areas show mean and SD values.