Figure 7. Lack of relationship between climate and soil δ¹⁵N after accounting for variation in clay concentrations.

Relationship between (A) clay concentrations in soil and residual soil δ¹⁵N after accounting for the relationship between soil δ¹⁵N and soil [C] (y = 1.71 + 2.01 × log(x), r² = 0.22, P < 0.001; n = 355). Also shown are relationships between (B) mean annual temperature (MAT), (C) mean annual precipitation (MAP) and residual soil δ¹⁵N after accounting for variation in soil [C], clay concentrations, and soil depth. Non-significant relationships are shown in gray. All points represent soil values averaged to 0.1° latitude and longitude.