Variation in foliar [sup 15]N abundance and the availability of soil nitrogen on Walker Branch Watershed
- ORNL, Oak Ridge, TN (United States)
Spatial patterns in natural [sup 15]N abundance ([sigma][sup 15]N) in soil, soil solutions, and non-N[sub 2]-fixing plants were studied in the deciduous forest on Walker Branch Watershed near Oak Ridge, Tennessee. This study was undertaken to test the hypothesis that foliar [sigma][sup 15]N values are related to the availability of inorganic nitrogen in mineral soil. Soils collected in or near valley bottoms on the watershed had higher levels of net nitrogen mineralization and net nitrification potential than those sampled from ridges and slopes. More positive foliar [sigma][sup 15]N values occurred in valley bottoms, which, relative to other positions on the watershed, were characterized by greater availability of soil nitrogen and lower C-to-N ratios in the O[sub 1]-horizon, in the surface mineral soil, and in autumn leaf fall. Although leaf nitrogen concentrations changed significantly over the course of the growing season, there was little seasonal variation in foliar [sigma][sup 15]N values. A hypothesis about the relative importance of different sources of nitrogen to the forest and how nitrogen cycling varies with topography in this nitrogen-deficient ecosystem was derived, in part, from spatial patterns in natural [sup 15]N abundance. There appear to be two processes affecting the topographic patterns in foliar [sup 15]N abundance on this watershed: (1) greater uptake from isotopically heavy pools of inorganic soil nitrogen by plants in valley bottoms, and (2) uptake of isotopically light ammonium-N in atmospheric deposition by plants on ridges and slopes (where the availability of inorganic soil nitrogen to plant roots is more limited). Results from this study indicate that foliar [sigma][sup 15]N values are positively correlated with net nitrification potential in surface soil. 34 refs., 13 figs., 8 tabs.
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 5978866
- Journal Information:
- Ecology; (United States), Vol. 74:7; ISSN 0012-9658
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
LEAVES
ABUNDANCE
NITROGEN
ECOLOGICAL CONCENTRATION
NITROGEN CYCLE
ECOSYSTEMS
SOILS
NITRIFICATION
TOPOGRAPHY
ENVIRONMENTAL EFFECTS
AVAILABILITY
PLANTS
ROOTS
SPATIAL DISTRIBUTION
TENNESSEE
CHEMICAL REACTIONS
DEVELOPED COUNTRIES
DISTRIBUTION
ELEMENTS
NONMETALS
NORTH AMERICA
USA
540210* - Environment
Terrestrial- Basic Studies- (1990-)