Global Patterns of the Isotopic Composition of Soil and Plant Nitrogen

From a societal perspective, soil N follows only soil C in the importance of soil to 21^st century environmental issues. Amundson et al (2003) developed a mass balance model for soil N and the ratio of ¹⁵N/¹⁴N, and provided the first global projections of the spatial patterns of soil and plant δ¹⁵N values. It was hypothesized that state factors, particularly climate, should drive broad patterns of soil and plant δ¹⁵N values in a manner analogous to the known patterns of total soil N (e.g. Post et al., 1984). At that time, the N isotope data available to explore the effect of individual factors was modest. In the past decade, numerous papers from a broad spectrum of locations have created a rich database that can be used to further refine the initial projections made more than a decade ago.

In this paper, hundreds of published measurements will be used to more deeply examine the climatic impacts on soil and plant δ¹⁵N values. Additionally, we will focus on the local controls of topography on ecosystem N cycling, which can create local isotopic variation that is similar in magnitude to the global effects of climate. The adoption of process-based models from the hillslope geomorphology community appears to be a powerful tool for explaining some existing data from toposequences, designing new studies of topographic controls on biogeochemistry, and particularly for parameterization in global models.

Amundson, R., A.T. Austin, E.A.G. Schuur, K. Yoo, V. Matzek, C. Kendall, A. Uebersax, D. Brenner, and W.T. Baisden. 2003. Global Biogeochemical Cycles 17(1):1031.