Carbon-nitrogen interactions in CO(2)-enriched white oak: physiological and long-term perspectives
Richard J. Norby1, John Pastor, Jerry M. Melillo
1Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Elevated atmospheric carbon dioxide (CO(2)) significantly increased white oak seedling growth and nitrogen-use efficiency. However, reduced translocatable nitrogen may limit future gains and impact soil nutrient cycling.
Area of Science:
- Forestry
- Plant Physiology
- Ecology
Background:
- Forest tree responses to elevated atmospheric CO(2) are influenced by carbon-nutrient dynamics.
- Understanding short-term physiological responses provides insights into long-term ecological consequences of CO(2) enrichment.
Purpose of the Study:
- To investigate the physiological responses of white oak (Quercus alba L.) seedlings to elevated CO(2) under nitrogen-limited conditions.
- To assess the impact of elevated CO(2) on growth, nitrogen uptake, and nutrient allocation in white oak seedlings.
Main Methods:
- One-year-old white oak seedlings were cultivated in controlled chambers for 40 weeks.
- Seedlings were exposed to either ambient (362 µL L⁻¹) or elevated (690 µL L⁻¹) CO(2) levels.
- Measurements included dry weight, nitrogen content, bud weight, and leaf litter composition.
Main Results:
- Seedling dry weight increased by 85% under elevated CO(2) without increased nitrogen uptake, indicating enhanced nitrogen-use efficiency.
- Elevated CO(2) led to greater bud weight, suggesting increased future shoot growth.
- Less translocatable nitrogen was found in woody tissues under elevated CO(2), potentially limiting further nitrogen-use efficiency gains.
Conclusions:
- Elevated CO(2) enhances white oak seedling growth and nitrogen-use efficiency, but this effect may be constrained by internal nitrogen availability.
- Changes in leaf litter composition (higher sugars, tannin; lower lignin) under elevated CO(2) could alter soil decomposition and nitrogen return rates.
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