Tropical forests and the global nitrous oxide budget
Jerry
M.
Melillo, Marine Biological Laboratory, jmelillo@mbl.edu
(Presenting)
Carlos
Clemente
Cerri, Centro de Energia Nuclear na Agricultura, cerri@cena.usp.br
Paul
A.
Steudler, Marine Biological Laboratory, steudler@mbl.edu
Diana
C.
Garcia-Montiel, Woods Hole Research Center, dgarcia@whrc.org
Christopher
Neill, Marine Biological Laboratory, cneill@mbl.edu
Brigitte
J.
Feigl, Centro de Energia Nuclear na Agricultura, beduardo@cena.usp.br
Nitrous oxide (N2O) is a long-lived and powerful greenhouse gas and its atmospheric concentration has been increasing over the past century. In recent decades, the annual rate of increase has been 0.25 ± 0.05%. Most of the increase in atmospheric N2O is currently unexplained although there is strong evidence that that the cause of the N2O trend appears to be a combination of a growing tropical source and a growing northern mid-latitude source. There is speculation that growth in the tropical source is related to tropical land-use disturbance. Here we offer a new explanation for part of the growing tropical source that involves tropical forests and an interaction between the cycles of carbon and nitrogen. We hypothesize that the growing tropical N2O source is in part a result of carbon dioxide (CO2) fertilization of tropical forests. The increase in atmospheric CO2 concentration stimulates forest productivity and the production of labile carbon compounds that move from the trees to the soil along several pathways. Once in the soil, these labile carbon compounds stimulate N2O production by soil microorganisms. We present data from our own field and modeling studies and data for other relevant research, including field measurements, remote sensing and modeling, to support this hypothesis.