Growth, nutrition, and nitrogen fixation in grey alder at varied rate of nitrogen addition [Alnus incana]
1980
Ingestad, T. (Sveriges Lantbruksuniversitet, Uppsala. Section of Forest Ecophysiology)
Seedlings of grey alder (Alnus incana Moench), nodulated or unnodulated, were investigated at varied relative addition rate of nitrogen. The nitrogen fixation rate was strongly stimulated by increasing nitrogen addition rate up to high levels. The fixation rate decreased rapidly close to optimum (maximum relative growth rate) and was negligible at maximum growth. A feed-back of mineral nitrogen on photosynthesis increased fixation rate with time, and the relative importance of fixation over mineral nitrogen nutrition increased. However, nitrogen fixation, also at maximum rate, supplied only a small proportion of the nitrogen amount required for maximum growth. The optimum nutrient solutions contained comparatively high nitrogen concentrations to secure free access to nitrogen. The nodules were damaged by this treatment, and it is concluded that the nitrogen additions must be adjusted to the current consumption of the plants to avoid an increased external nitrogen concentration. Strong linear regressions were found between relative growth rate, nitrogen status expressed as percentage content of fresh weight, and relative growth rate in unnodulated seedlings. There was a greater variability in nodulated seedlings than in unnodulated ones, because of the nitrogen fixation. The reactions of unnodulated grey alder were largely the same as previously reported for birch seedlings, but the maximum growth capacity was lower in grey alder. During an initial period of change in the internal nitrogen status, deficiency symptoms appeared, especially in unnodulated seedlings. As in birch, the leaves turned green again at stable nitrogen status, independent of level
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