ABSTRACT

This project involves basic research of controls on nitrogen (N) weathering rates from bedrock across an array of terrestrial ecosystems and conditions ? spanning molecular techniques to global scale modeling. This study is motivated by the need to understand how biogeochemical cycles shape integrated Earth systems and has key implications for the pace and magnitude of climate change in the face of rising fossil fuel CO2 emissions. Bedrock lithologies house >99% of all reactive N compounds (i.e., all N forms other than N2 gas) on the planet; yet, the biogeochemical importance of this vast N reservoir has been overlooked. Textbook paradigms hold that new N enters ecosystems solely from the atmosphere via biochemical fixation or as N in deposition. However, these N input pathways are incapable of explaining the high rates of N accumulation observed for many terrestrial ecosystems, constituting a major unknown in the global N budget.

As an alternative, the principal investigators suggest that the geosphere plays a major role in terrestrial N biogeochemistry ? imparting large effects on terrestrial carbon (C) cycling and climate change. They propose research to test the hypothesis that rocks of sedimentary origin represent a broadly significant source of N to the terrestrial biosphere. The research team includes geologists, biologists, pedologists, biogeochemists, and Earth system scientists. They will examine bedrock N weathering at molecular-, soil pedon-, watershed-, regional-, and global-scales. The proposed combination of state-of-the-art tools, involving lab, field, and modeling components, is novel. The molecular-scale research is focused on geobiology; it emphasizes ?rock-eating-fungi? effects on N weathering reactions, using controlled laboratory experiments and NanoSIMS (Nanometer-scale Secondary Ion Mass Spectrometry) across field sites. The soil pedon, watershed and regional analyses will estimate physical and chemical weathering of nitrogen across an array of lithologies, tectonic conditions, and climates. Linkages between weathering rates and the terrestrial nitrogen cycle will be empirically investigated regionally through measures of natural nitrogen stable isotopes, and carbon, nitrogen, and phosphorus chemistry. The global analyses will emphasize a new modeling scheme that couples a global biogeochemical model with a weathering model to scale the amount of rock-derived nitrogen that is available to store terrestrial carbon worldwide.

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