Bedrock weathering controls on terrestrial carbon-nitrogen-climate interactions

Anthropogenic nitrogen deposition is widely considered to increase
CO2 sequestration by land plant communities on a global scale.
Here, we suggest that bedrock nitrogen weathering contributes
significantly more to nitrogen-carbon interactions than anthropogenic
nitrogen deposition. This working hypothesis is based on the application
of empirical results into a global biogeochemical simulation model from
the mid-1800s to the end of the 21st century. We demonstrate that rock
nitrogen inputs have contributed roughly 2 to 11 times more to net primary
productivity gains than nitrogen deposition since pre-industrial times.
Projections based on RCP 8.5 show that rock nitrogen inputs and biological
nitrogen fixation contribute 2 to 5 times more to terrestrial carbon
uptake than anthropogenic nitrogen deposition through year 2101. The
enhancement of carbon uptake via rock nitrogen weathering partially
resolves nitrogen-carbon discrepancies in Earth system models and offers
an alternative explanation for lack of progressive nitrogen limitation in
the terrestrial biosphere. We conclude that natural N inputs
impart major control over terrestrial CO2 sequestration in Earth’s
ecosystems.