Nitrogen and carbon source-sink relationships in trees at the Himalayan treelines compared with lower elevations
Mai-He Li1, Wen-Fa Xiao, Peili Shi
1Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland. maihe.li@wsl.ch
Plant, Cell & Environment
|July 23, 2008
Summary
Alpine treeline formation is not limited by nitrogen. Trees may face winter carbon shortages, suggesting a need for sufficient non-structural carbohydrates (NSC) and a balanced carbon source-sink relationship for survival.
Area of Science:
- Ecology
- Plant Physiology
- Biogeography
Background:
- The mechanisms driving alpine and arctic treeline formation remain poorly understood, with no single unifying hypothesis.
- Existing theories often focus on factors like photosynthesis, carbon balance, and nutrient availability.
Purpose of the Study:
- To investigate the primary determinants of alpine treeline formation.
- To test hypotheses related to nitrogen content, carbon gain, source-sink ratios, and carbon-nitrogen ratios in treeline trees.
Main Methods:
- Analysis of needle nitrogen content in Himalayan treeline trees.
- Assessment of non-structural carbohydrate (NSC) levels, including sugar and starch concentrations.
- Evaluation of carbon source-sink relationships within treeline tree physiology.
Main Results:
- Nitrogen availability was found not to limit the growth of trees at Himalayan treelines.
- Non-structural carbohydrate levels exhibited species-specific and site-dependent variations, indicating no consistent carbon or growth limitation.
- Combined data from three treelines suggested a potential for winter carbon shortage in treeline trees.
Conclusions:
- Treeline formation is not solely dictated by nitrogen content or simple carbon gain limitations.
- Sufficient non-structural carbohydrate reserves, a high sugar-to-starch ratio, and a balanced carbon source-sink relationship are crucial for treeline tree persistence in harsh alpine environments.
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