PARENT SESSION
Oral Session #35: Nitrogen cycling: Response to inputs, variation in time and space. Presiding: M. Fenn.
Tuesday, August 7, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.

Effects of N additions on N-oxide emissions and soil N dynamics across a matrix of land use, elevation, soil age, and soil type on Mt. Kinabalu, Borneo (Malaysia).

HALL, SHARON¹, ASNER, GREGORY¹, KITAYAMA, KANEHIRO², ^{1 2}

ABSTRACT- Concentrations of nitrous oxide (N₂O) and nitric oxide (NO_x = NO + NO₂) are increasing in the atmosphere primarily due to fossil fuel emissions and fertilized agriculture. In addition, increased atmospheric N deposition may increase soil N-oxide emissions from soils in the future, particularly in highly-weathered systems in the tropics. We explored the effects of N additions, land-use, elevation, soil age, and soil type on the emissions of N₂O and NO_x from soils in humid tropical systems on Mt. Kinabalu, Borneo (Malaysia). In forests, N-oxide emissions after a range of N additions were significantly correlated with activity of nitrifying microorganisms and N availability (r² = 0.6 - 0.9, p ≤ 0.01-0.1). Fluxes after N additions ranked as following (from highest to lowest): Low elevation sedimentary ≥ high elevation sedimentary (young substrate) > high elevation sedimentary (old substrate) > low elevation serpentine > high elevation serpentine. Background emissions from forests were largest on sedimentary substrates and decreased with elevation up to 3100 m. As expected, N-oxide emissions from agricultural systems were controlled by irrigation and fertilizer management rather than by substrate type.

KEY WORDS: nitrous oxide, nitrification, tropical forest, SE Asia