Cumming J R, Brown S M
Department of Botany, University of Vermont, Burlington, VT 05405-0086, USA.
Tree Physiol. 1994 Jun;14(6):589-99. doi: 10.1093/treephys/14.6.589.
Acidic deposition in high-elevation forests in the Appalachian Mountains of the eastern United States has been implicated in the decline of red spruce (Picea rubens Sarg.). Elevated soil acidity may increase soil Al availability and toxicity to roots. Enhanced soil solution NO(3) (-) concentrations, resulting from precipitation inputs and enhanced soil organic matter mineralization, may exacerbate Al toxicity by increasing root Al uptake. We exposed red spruce seedlings to 350, 500, 800 or 1400 micro M NO(3) (-) and 0 or 200 micro M Al in a factorial design in sand-nutrient solution culture to test if increased NO(3) (-) concentrations enhance Al uptake and toxicity. In addition to significant reductions in seedling growth parameters resulting from Al exposure, we found significant interactions between NO(3) (-) and Al for seedling height growth rate, needle weight, shoot weight and root weight. Differences in these parameters between Al treatments became more pronounced as solution NO(3) (-) concentration increased and reflected an Al-mediated inhibition of seedling response to increasing NO(3) (-) concentration. Solution NO(3) (-) concentrations above 500 micro M induced root nitrate reductase (NR) activity, whereas shoot NR activity increased in response to NO(3) (-) up to 500 micro M and declined above that concentration. In contrast, exposure to Al depressed NR activity of roots but tended to stimulate needle NR activity. Foliar N concentrations increased in seedlings grown in cultures containing between 350 and 500 micro M NO(3) (-), with no change above 500 micro M. Increasing concentrations of NO(3) (-) depressed foliar P concentrations, with reductions being greatest in seedlings exposed to 1400 micro M NO(3) (-). Exposure to Al increased foliar Ca, K and Al concentrations, decreased foliar P concentrations, and inhibited increases in foliar Mg concentration in response to increasing NO(3) (-). The consistent interactions between NO(3) (-) and Al for growth, root NR activity and foliar Mg concentration were the result of an inhibition of seedling response to NO(3) (-) mediated by Al in solution, rather than enhanced Al toxicity resulting from growth in the presence of elevated NO(3) (-) concentrations.
美国东部阿巴拉契亚山脉高海拔森林中的酸性沉降被认为与红云杉（Picea rubens Sarg.）的衰退有关。土壤酸度升高可能会增加土壤中铝的有效性及其对根系的毒性。降水输入和土壤有机质矿化增强导致土壤溶液中硝酸根离子（NO₃⁻）浓度升高，这可能会通过增加根系对铝的吸收而加剧铝的毒性。我们在砂质营养液培养中采用析因设计，将红云杉幼苗暴露于350、500、800或1400微摩尔/升的NO₃⁻以及0或200微摩尔/升的铝中，以测试增加的NO₃⁻浓度是否会增强铝的吸收和毒性。除了铝暴露导致幼苗生长参数显著降低外，我们还发现NO₃⁻和铝在幼苗高度生长速率、针叶重量、地上部分重量和根系重量方面存在显著的交互作用。随着溶液中NO₃⁻浓度的增加，铝处理之间这些参数的差异变得更加明显，这反映了铝对幼苗对增加的NO₃⁻浓度反应的抑制作用。溶液中NO₃⁻浓度高于500微摩尔/升时会诱导根系硝酸还原酶（NR）活性，而地上部分NR活性在NO₃⁻浓度达到500微摩尔/升时会增加，高于该浓度则会下降。相比之下，铝暴露会降低根系的NR活性，但往往会刺激针叶的NR活性。在含有350至500微摩尔/升NO₃⁻的培养物中生长的幼苗叶片氮浓度会增加，高于500微摩尔/升时则没有变化。NO₃⁻浓度增加会降低叶片磷浓度，在暴露于1400微摩尔/升NO₃⁻的幼苗中降低幅度最大。铝暴露会增加叶片钙、钾和铝的浓度，降低叶片磷浓度，并抑制叶片镁浓度随NO₃⁻浓度增加而升高。NO₃⁻和铝在生长、根系NR活性和叶片镁浓度方面持续存在的交互作用是溶液中铝介导的对幼苗对NO₃⁻反应的抑制作用的结果，而不是在高浓度NO₃⁻存在下生长导致铝毒性增强的结果。
