Event Title

Elevated Stream Inorganic Nitrogen Impacts on a Dominant Riparian Tree Species: Results from an Experimental Riparian Stream System

Presenter Information

Kevin R. Hultine

Location

ECC 203

Event Website

https://water.usu.edu/

Start Date

3-31-2008 11:00 AM

End Date

3-31-2008 11:15 AM

Description

The release of inorganic nitrogen from intensive agricultural practices and urbanization has resulted in significant alterations of the aquatic nitrogen cycle in riparian ecosystems. Yet impacts of stream nitrogen inputs on the terrestrial nitrogen cycle, as well as water and carbon cycles are unclear. Information on terrestrial ecosystem responses to stream N loading is largely absent, in part due to the difficulty in controlling for temporal and spatial variation in streamflow, geomorphology, climate and vegetation. To address these issues, we constructed a dual-plot artificial stream riparian system within a 10-year old plantation of a dominant riparian tree species; box elder (Acer negundo). The dual-plot design allowed for varying concentrations of stream inorganic nitrogen between plots, while controlling for ecohydrologic and geohydrologic variability. The system was used to investigate elevated inorganic stream impacts on water use patterns, above ground productivity, and leaf chemistry of streamside box elder trees over two consecutive growing seasons (2006 and 2007). One plot received inorganic soluble fertilizer that brought the NO3 concentration of stream water from 5 mmol l-1 to about 100 mmol l-1, while the second plot received no additional nitrogen. Relative stem sap flux density (Js) did not vary between plots until near the conclusion of the 2006 growing season, when trees in the fertilized plot showed a steep upswing in Js relative to trees in the control plot. Sap flux in 2007 increased consistently by 0.4% day-1 in the fertilized plot relative to the control plot over a 75-day period, before leveling off near the conclusion of the growing season. At the onset of the experiment, leaf nitrogen per unit mass and leaf nitrogen per unit area, were significantly higher in the control plot and leaf C:N ratios were lower. In 2007, however, differences in leaf chemistry disappeared, suggesting that leaf nitrogen increased in the fertilized trees relative to the control trees. Stem diameter growth in 2007 was 25% greater in the fertilized trees, although there were no differences in either leaf area or canopy height growth throughout the experiment. Results from this investigation suggests that increases in stream inorganic nitrogen effect water use, litter quality, and productivity of dominant riparian vegetation. These effects may have important feedbacks on several ecohydrological processes.

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Mar 31st, 11:00 AM Mar 31st, 11:15 AM

Elevated Stream Inorganic Nitrogen Impacts on a Dominant Riparian Tree Species: Results from an Experimental Riparian Stream System

ECC 203

The release of inorganic nitrogen from intensive agricultural practices and urbanization has resulted in significant alterations of the aquatic nitrogen cycle in riparian ecosystems. Yet impacts of stream nitrogen inputs on the terrestrial nitrogen cycle, as well as water and carbon cycles are unclear. Information on terrestrial ecosystem responses to stream N loading is largely absent, in part due to the difficulty in controlling for temporal and spatial variation in streamflow, geomorphology, climate and vegetation. To address these issues, we constructed a dual-plot artificial stream riparian system within a 10-year old plantation of a dominant riparian tree species; box elder (Acer negundo). The dual-plot design allowed for varying concentrations of stream inorganic nitrogen between plots, while controlling for ecohydrologic and geohydrologic variability. The system was used to investigate elevated inorganic stream impacts on water use patterns, above ground productivity, and leaf chemistry of streamside box elder trees over two consecutive growing seasons (2006 and 2007). One plot received inorganic soluble fertilizer that brought the NO3 concentration of stream water from 5 mmol l-1 to about 100 mmol l-1, while the second plot received no additional nitrogen. Relative stem sap flux density (Js) did not vary between plots until near the conclusion of the 2006 growing season, when trees in the fertilized plot showed a steep upswing in Js relative to trees in the control plot. Sap flux in 2007 increased consistently by 0.4% day-1 in the fertilized plot relative to the control plot over a 75-day period, before leveling off near the conclusion of the growing season. At the onset of the experiment, leaf nitrogen per unit mass and leaf nitrogen per unit area, were significantly higher in the control plot and leaf C:N ratios were lower. In 2007, however, differences in leaf chemistry disappeared, suggesting that leaf nitrogen increased in the fertilized trees relative to the control trees. Stem diameter growth in 2007 was 25% greater in the fertilized trees, although there were no differences in either leaf area or canopy height growth throughout the experiment. Results from this investigation suggests that increases in stream inorganic nitrogen effect water use, litter quality, and productivity of dominant riparian vegetation. These effects may have important feedbacks on several ecohydrological processes.

https://digitalcommons.usu.edu/runoff/2008/AllAbstracts/4