Scaling Biogenic Trace Gas Emissions from Plots to Landscapes Using Airborne Spectroscopic Estimates of Canopy Nitrogen Content: Progress and Limitations.
Sharon J. Hall, Arizona State Univ., Ecol., Evol. and Environ. Sci., Box 874501, Life Sciences C-274, Tempe, AZ 85276-4501
Soils are estimated to be the largest natural source of nitrous oxide (N2O) globally, but annual and regional budgets for these gases are limited by large variability in fluxes over space and time. We sampled N2O fluxes and nitrogen transformations from soils influenced by an invasive, N-fixing tree (Morella faya) in HawaiiVolcanoesNational Park, and we used novel, airborne spectroscopic techniques and photon transport modeling to extrapolate emissions to the landscape scale. Field measurements of soil trace gases correlated well with canopy N content in wet tropical forest sites where M. faya has increased soil N2O emissions by an order of magnitude compared to native forest stands. In contrast, remotely based estimates of canopy N were not related to soil N-oxide emissions in tropical dry forests where water rather than nutrients limit primary production and soil biogeochemical cycling. Our results suggest that remote sensing techniques will help to refine regional estimates of N-oxide emissions from soils when combined with ground-based field measurements and modeling efforts, but the methods used will differ by ecosystem type.