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.