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Plant Cell Environ ; 31(10): 1377-87, 2008 Oct.
Article in English | MEDLINE | ID: mdl-18643956

ABSTRACT

No single hypothesis or theory has been widely accepted for explaining the functional mechanism of global alpine/arctic treeline formation. The present study tested whether the alpine treeline is determined by (1) the needle nitrogen content associated with photosynthesis (carbon gain); (2) a sufficient source-sink ratio of carbon; or (3) a sufficient C-N ratio. Nitrogen does not limit the growth and development of trees studied at the Himalayan treelines. Levels of non-structural carbohydrates (NSC) in trees were species-specific and site-dependent; therefore, the treeline cases studied did not show consistent evidence of source/carbon limitation or sink/growth limitation in treeline trees. However, results of the combined three treelines showed that the treeline trees may suffer from a winter carbon shortage. The source capacity and the sink capacity of a tree influence its tissue NSC concentrations and the carbon balance; therefore, we suggest that the persistence and development of treeline trees in a harsh alpine environment may require a minimum level of the total NSC concentration, a sufficiently high sugar:starch ratio, and a balanced carbon source-sink relationship.


Subject(s)
Altitude , Carbon/metabolism , Nitrogen/metabolism , Trees/metabolism , Abies/growth & development , Abies/metabolism , Analysis of Variance , Carbohydrates/biosynthesis , China , Ecosystem , Geography , Photosynthesis , Picea/growth & development , Picea/metabolism , Trees/growth & development
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