Effects of chronic low-level N additions on foliar elemental concentrations, morphology, and gas exchange of mature montane red spruce

Abstract

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 n1 ·year n1 . 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. Resume : Les auteurs ont OvaluO liinfluence diune fertilisation prolongOe avec de faibles niveaux diazote (N) sur 29 paramtres morphologiques, physiologiques et chimiques mesurOs sur des Opinettes rouges ( Picea rubens Sarg.) matures croissant dans 10 parcelles-Ochantillons sur le mont Ascutney dans le Vermont. Pendant 8 annOes consOcutives antOrieures ‡ cette Otude, chaque parcelle a reAu un des cinq traitements suivants : 0, 15,7, 19,8, 25,6 ou 31,4 kg N·ha n1 ·an n1 . Comparativement au matOriel vOgOtal provenant des parcelles tOmoins, les arbres qui avaient reAu une fertilisation azotOe