Evaluation of the stem injection technique and subsequent 15 N partitioning in red alder crowns

Abstract

Red alder (Alnus rubra Bong.) trees were labeled with 15 NO 3 or 15 NH 4 using the stem-injection method. Leaves were sampled 3 and 15 months subsequent to injection within several crown positions, including top, bottom, proximal, medial, and distal. Stem injection of both 15 NH 4 and 15 NO 3 at levels approaching 1% of crown N effectively labeled red alder trees. Although more variable, 15 NO 3 may have been more efficient in initial labeling. The distribution of 15 N in the crown was uniform 3 months after labeling, but was diluted in the distal and top positions by the following year. In both years there was a clear increase in total N concentration toward the periphery of the tree. This increase became more pronounced with increasing crown size and crown closure. Crown position with respect to light availability may be the most important determinant in N allocation in red alder foliage.