Nitrogen cycling in dense plantings of hybrid poplar and black alder |
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Authors: | B Côté C Camiré |
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Institution: | (1) Département des sciences forestières, Faculté de foresterie, Université Laval, G1K 7P4 Ste-Foy, Qué., Canada |
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Abstract: | Summary Nitrogen cycling was studied during the third growing season in pure and mixed plantings (33×33 cm spacing) of hybrid poplar and black alder in southeastern Canada. After 3 years, hybrid poplar growth and N content of living tissues in a plot and of individual hybrid poplar plants increased with the proportion of black alder in a planting. No differences were detected among N contents of individual alder plants regardless of plot treatment. Black alder allocated a larger portion of its N to roots than hybrid poplar. Symbiotic nitrogen fixation was estimated to account for 80% of the nitrogen in aboveground alder tissues in the pure treatment using natural15N dilution. N return in leaf litter was estimated to be 70kg ha–1 in the pure alder treatment and decreased to a minimum of 20 kg ha–1 in the pure hybrid poplar plots. No difference was detected among treatments for throughfall N content. Nitrogen concentration in roots and leaf litterfall of black alder was higher than hybrid poplar. Significant soil N accretion occurred in mixed plantings containing two alders to one poplar and pure black alder plantings. Nitrogen availability (NO3–N) increased with the amount of black alder in a plot. Results suggest that the early increase in nitrogen accumulation of hybrid poplar in mixed treatments can be attributed to an increase of total soil N availability resulting from the input of large amounts of N from easily mineralizable alder tissue. |
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Keywords: | Alnus glutinosa Black alder Dinitrogen fixation Hybrid poplar Nitrogen Nitrogen cycling Short-rotation plantation |
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