Nitrogen (N) limits primary production across much of the land and ocean, and thus nitrogen cycling has been the focus of intense study for decades. Nevertheless, major pathways of N loss from ecosystems remain poorly constrained, in part because losses of dinitrogen (N2) are difficult to measure in a background atmosphere that is 80% N2. This is particularly true in the lowland tropics, which typically cycle N in excess of biological demand and thus have a high potential for N2 gas loss. If the amount of N loss from tropical soils is poorly constrained, so too is the chemical form of soil N emissions. Yet these forms have dramatically different effects. Nitric oxide (NO) is a precursor to smog in cities and a key component of acid rain. Nitrous oxide (N2O) is a powerful greenhouse gas and consumer of stratospheric ozone. Dinitrogen is inert and environmentally benign. The proportion of these gases emitted from soils probably varies across both space and time, and our inability to quantify this variation is a major obstacle to building a more robust understanding of tropical N cycling.
My thesis will focus on the amount, form, and controls of N gas losses from a tropical forest in Puerto Rico. I will use a new technique for measuring N gas emissions and chemistry to ask four fundamental questions:
1) How do ecosystem properties that drive variation in soil oxygen (O2) influence emissions of N2O and N2, and what are the estimated annual emissions of N2 produced from a tropical forest?
2) How do ecosystem properties that drive variation carbon (C) and N influence emissions of N2O and N2?
3) How will the ratio and/or magnitude of N2O and N2 emitted change in response to increased N deposition?
4) How will the ratio and/or magnitude of N2O and N2 emitted change in response to increased temperature?