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Nitrogen and phosphorus retranslocation from needles of douglas-fir growing on three site-types Parkinson, Joy Anne


Nitrogen and phosphorus retranslocation from needles of Douglas-fir growing on xeric, mesic and hygric sites of the drier subzone of the Coastal Western Hemlock Zone (Krajina, 1969) was estimated by comparing the content in current needles and in needle litter. Linear relationships between nutrient content in current needles and the amount retranslocated (absolute loss) were found to be site-specific and analysis of covariance was used to correct absolute loss for between-site differences in the content of current needles. The absolute loss of nitrogen was significantly higher (p=.05 for all tests) on the mesic sites than on the hygric or xeric sites. Phosphorus retranslocation was significantly different between the three site-types with the hygric having the highest and the xeric the lowest absolute loss. The differences may be explained by the balance between availability and demand for nitrogen and phosphorus on the respective sites. Several other possible reasons for the low retranslocation rates on xeric sites are discussed. No significant difference in needle nitrogen concentration was found between sites. Phosphorus content was lower in needles on the hygric sites than on the xeric or mesic, but for P concentration, an interaction between crown level, hygrotope and needle age prevented statistical analysis. For both elements, the interaction between crown level and needle age indicated that changes in nutrient content and concentration with needle age differed between crown levels. The literature contains a number of variations on the techniques used to evaluate internal cycling and, therefore, careful definition of terms is suggested when comparing between studies.

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