Effects of chronic low-level N additions on foliar elemental concentrations, morphology, and gas exchange of mature montane red spruce
1997
Schaberg, P.G. | Perkins, T.D. | McNutty, S.G.
We evaluated the influence of protracted low-level nitrogen (N) fertilization on 29 morphological, physiological, or chemical parameters measured on mature red spruce (Picea rubens Sarg.) growing within 10 study plots on Mount Ascutney, Vermont. For 8 consecutive years prior to this study, each plot received one of five treatments: 0, 15.7, 19.8, 25.6, or 31.4 kg N.ha-1.year-1. In comparison to plant material from control plots, trees that received N fertilization had fewer but longer and heavier needles, and higher rates of shoot water loss than trees from control plots. N fertilization resulted in increased foliar N concentrations, and reductions in foliar Ca and Mg concentrations to potentially deficient levels. Although no differences in chlorophyll content, chlorophyll fluorescence, or net photosynthesis were evident, N fertilization was associated with increased levels of respiration. Respiration rates were not correlated with foliar N concentrations, suggesting that the influence of N treatment on respiration was indirect. In contrast, respiration levels were negatively correlated with foliar Ca and Mg concentrations. Although we have no direct evidence that they are related, the N-induced alterations in foliar cation and respiration levels that we found may help account for N-induced reductions in tree growth and increases in mortality previously reported for this site.
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