Data from: Isotopic evidence for oligotrophication of terrestrial ecosystems

Human societies depend on an Earth System that operates within a
constrained range of nutrient availability, yet the recent trajectory of
terrestrial nitrogen (N) availability is uncertain. Examining patterns of
foliar N concentrations ([N]) and isotope ratios (15N) from more than
42,000 samples acquired over 37 years, here we show that foliar [N]
declined by 8% and foliar 15N declined by 0.8 – 1.9 ‰. Examining patterns
across different climate spaces, foliar 15N declined across the entire
range of MAT and MAP tested. These results suggest declines in N supply
relative to plant demand at the global scale. In all, there are now
multiple lines of evidence of declining N availability in many
unfertilized terrestrial ecosystems, including declines in 15N of tree
rings and leaves from herbarium samples over the past 75-150 years. These
patterns are consistent with the proposed consequences of elevated
atmospheric CO2 and longer growing seasons. These declines will limit
future terrestrial C uptake and increase nutritional stress for
herbivores.