Document: CAR-3-76-5

The influence of nitrogen availability on the establishment of Fremont cottonwood seedlings along the Yampa River.

ADAIR, E.C.* and D.BINKLEY

Colorado State University, Fort Collins, CO 80523 USA ¹

Abstract:
Nutrient availability strongly affects the species composition and productivity of most upland ecosystems, but the importance of nutrient availability is largely undefined for riparian ecosystems in arid regions of the western United States. The establishment and persistence of cottonwood (Populus spp.) seedlings is dependent principally on an intact flooding regime. This major role of water does not preclude an important role for nutrient availability. The uptake and efficient use of water may depend on nutrient supply. First year cottonwood seedlings typically extend only about 30cm into the soil. If nutrient supply regulates seedling root growth, higher nutrient availability might allow deeper root penetration, and shorten the 3 to 5 year period required for roots to reach the seasonal water table. To investigate how nitrogen availability influences the composition and productivity of riparian communities, we tested the hypothesis that the development of first year Fremont cottonwood seedlings is limited by soil nitrogen availability. Plots of naturally germinated cottonwood seedlings were randomly assigned one of four treatments: Water only, nitrogen only, water and nitrogen, or control. ANOVA analysis of the plots indicated that N was significant for total seedling length (p = 0.05), shoot length (p = 0.01), and root length (p = 0.07). Water addition increased shoot length (p = 0.02) and total length (p = 0.10), but not root length (p = 0.21). Cottonwood seedling establishment therefore appears to be limited by nitrogen availability. Altering the hydrologic regime of a river affects the rates and timing of nutrient cycles. The resulting changes in the patterns of nutrient availability and accumulation could therefore affect ecosystem composition and productivity.

Keywords: riparian vegetation, cottonwood, seedling establishment, Colorado, nitrogen

This abstract is being presented at: 11:15 AM in session:
Oral Session #41: N Dynamics: Additions, Retention and Transformations.