Document: AMY-3-33-17

Differential utilization of N by co-occurring alpine tundra species: Field and greenhouse evidence.

MILLER, A.E.* and W.D.BOWMAN

University of Colorado, Boulder, CO, USA ¹

Abstract:
The degree to which species within a single plant community vary in their patterns of N utilization is not well understood. In N-limited environments such as the alpine tundra, plants may utilize a diversity of N sources (organic and inorganic) in order to meet their nutritional requirements. To characterize species-level differences in traits related to N acquisition and use, we analyzed foliar tissue from 10 alpine species for ¹⁵N, N concentration, and in vivo nitrate reductase activity (NRA). Roots were examined for mycorrhizal infection, and depth of root activity was estimated from recovery of a Rb tracer injected at two depths. Results of this work and a previous ¹⁵N tracer addition conducted in the greenhouse indicate that co-occurring species differ significantly in isotopic signature, NRA, and N uptake patterns, and that these differences may be more closely related to root morphology and mycorrhizal associations than to growth form. Species exhibiting the most negative ¹⁵N signatures in the field also showed relatively high NRA and approximately 50% greater uptake of NO₃^- than NH₄⁺, whereas species exhibiting the most positive ¹⁵N signatures tended to show a disproportionate uptake of NH₄⁺. Uptake of organic N (glycine) appeared to be intermediate for most species. These data indicate that co-occurring species are capable of using divergent N sources, and may represent one mechanism by which plants partition a limited N pool.

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This abstract is being presented at: 8:15 AM in session:
Oral Session #61: Plant Responses to Nutrients.