Bench-grafter Fuji/M.26 apple (Malus domestica Borkh.) trees were fertigated for 45 d with different nitrogen concentrations in modified Hoagland's solutions. A wide range of leaf N content was noted in recently fully expanded leaves (from 0.9-4.4 g m~(-2)). Apparent quantum efficiency for CO_2 assimilation was relatively constant except for a slight decrease at the lower end of the leaf N range. The light saturation point for CO_2 assimilation increased with increasing leaf N. Curvilinear relationships were found between leaf N and 1) light-saturated CO_2 assimilation at ambient CO_2 2) the initial slope of the response of CO_2 assimilation to intercellular CO_2 concentration, and 3) CO_2 saturated photosynthisis. All three initially increased linearly with increasing leaf N, then reached a plateau at a leaf N content of approximately 3 g m~(-2). The relationship between leaf N and stomatal conductance was similar to that of CO_2 assimilation with leaf N. Calculated intercellular CO_2 concentration, however, tended to decrease with increases in leaf N, indicating that stomatal conductance did not limit photosynthesis in leaves with low N content. Light-saturated CO_2 assimilation, expressed on a leaf N basis, decreased with increasing leaf N. A curvilinear relationship existed between leaf N content and photosynthetic capacity in apple leaves. Photosynthetic N use efficiency decreased with increasing leaf N content.
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机译：在改良的Hoagland's溶液中，用不同的氮素浓度将富士/M.26苹果（Malus domestica Borkh。）台式嫁接树施肥45 d。在最近完全膨大的叶片中，叶片的氮含量范围很广（从0.9-4.4 g m〜（-2））。除了在叶片N范围的下端略有降低外，CO_2同化的表观量子效率相对恒定。 CO_2同化的光饱和点随叶片N的增加而增加。在叶片N和1）在环境CO_2处的光饱和CO_2同化之间存在曲线关系; 2）CO_2同化对细胞间CO_2浓度的响应的初始斜率，以及3） CO_2饱和光合作用。这三个叶片最初均随叶N的增加呈线性增加，然后在叶N含量约为3 g m〜（-2）时达到平稳状态。叶片氮与气孔导度之间的关系类似于与叶片N吸收CO_2的关系。但是，计算得出的细胞间CO_2浓度会随着叶片N的增加而降低，这表明气孔导度不会限制低氮含量叶片的光合作用。以叶N为基础表达的光饱和CO_2同化随着叶N的增加而降低。苹果叶片中叶N含量与光合能力之间存在曲线关系。随着叶片氮含量的增加，光合氮的利用效率降低。
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