Figure 8
Carbon and nitrogen isoscapes. (a) Modern P. australis showing the sharp, 2.0‰ contrast in mean δ13C between eastern and western clusters and the two-tailed Student’s t-test p-value from Table 2. (b) Ancient Great Wall Phragmites have more homogenous δ13C values across eastern and western clusters, with western samples being 0.5‰ lighter than their eastern counterparts on average. Also shown is the two-tailed Student’s t-test p-value for all ancient Phragmites from eastern (Sites 1–7) and western (Sites 8–14) clusters. Although both p-values are < 0.05, (a) and (b) demonstrate the large 2.5 ‰ difference between modern and ancient samples from the western cluster following 21st Century warming. (c) Highly variable δ15N values likely suggest evidence of fertilization in some sites, specifically Milan Castle (Site 8) and Sishilidadun Tower (Site 14). Maps were created using the Kriging feature in ArcGIS Pro, whereby color variation in the surface reflects the spatial correlation between δ13C or δ15N values.
