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Abstract
This study measured the amount of uptake of labeled nitrogen (15N) of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm) seedlings, at three different phenological stages, in a growth chamber experiment. Thirty days after 15N application, the amount of 15N recovered in seedlings as a percentage of the total 15N fertilizer applied was 4% in early spring, 43% in summer and 33% in autumn. The total 15N recovered in the plant–pot system ranged from 80 to 96%, and is higher than reported in other studies. Total 15N recovered from the pot compartment alone ranged from 48 to 95%, suggesting that substantial pools of N remain in the soil. Results suggest that low 15N uptake in the spring was associated with limited development of new root as a result of low spring soil temperatures. The lack of unsuberized roots in spring could be a key factor decreasing the effectiveness of early spring fertilization in the boreal forest.
Acknowledgments
We thank Dr Thompson Nunifu for field assistance; Kevin Bladon, Wolf Liu, Lynn Reich, Bryn Jonson, Nicola Wilson and Heather Fish for laboratory assistance; and Laki Goonewardene and Emmanuel Mapafumo for statistical advice. We thank Clive Figueiredo for the 15N analysis. Seedlings were provided by Weldwood of Canada. Funding for this research was generously provided by Weldwood of Canada, Weyerhaeuser Canada and the National Sciences and Engineering Research Council of Canada. We thank the Faculty of Graduate Studies and Research for financial support through Graduate Research assistantship. We also thank the Editor and three anonymous referees for the suggestions and comments on the manuscript.