Document: RON-3-59-75

Global patterns of the isotopic composition of soil nitrogen.

AMUNDSON, R.* ¹, D.BRENNER ¹, W.T.BAISDEN ¹, A.MILLER ¹ and C.KENDALL ²

University of California, Berkeley, CA 94720 ¹
US Geological Survey, Menlo Park, CA ²

Abstract:
We compiled new and published data on the N isotope composition of soil organic matter from around the world. As previously reported, soil N isotope values decrease with increasing mean annual precipitation (MAP), but also show an increase with an increase of mean annual temperatures (MAT). Within any climatic zone, there can be a large observed range in delta 15N values due to variations in soil age, parent material, and topography. Because most undisturbed global soils are at or near N and N isotope steady state, it appears that (at a global scale) an increasing fraction of the annual N leaving soils is composed of ¹⁵N-depleted forms (NO₃, N₂O, N₂, etc.) with decreasing MAP and increasing MAT. This interpretation, based on mass balance considerations, suggests that wet ecosystems lose smaller fractions of their N over geological time spans in mineralized forms, implying that these ecosystems are efficient in conserving and recycling mineral N. In these ecosystems, the pervasive form of N loss must be in particulate or dissolved organic forms. In contrast, the N isotope data suggest that dry (or seasonally dry) and warm ecosystems appear to produce mineralized forms of N that exceed ecosystem biological demand.

Keywords: soil N, N isotopes, climate

This abstract is being presented at: 3:30 PM in session:
Poster Session #15: Nutrient Cycling.