Sadras V O, Hall A J, Connor D J
IFEVA, Facultad de Agronomia, Universidad de Buenos Aires, Av San Martin 4457, 1417, Buenos Aires, Argentina.
Oecologia. 1993 Oct;95(4):488-494. doi: 10.1007/BF00317432.
In vegetative canopies of many species, the vertical gradient of lamina nitrogen concentration (NW) parallels the profile of light distribution in such a way that the actual nitrogen partitioning approaches the optimum pattern for canopy photosynthesis. This paper evaluates the hypothesis that a strong sink for nitrogen, viz. growing grain, affects the pattern of lamina nitrogen distribution usually described for vegetative canopies. The light and NW profiles of sunflower (Helianthus annuus L.) crops were characterised from anthesis to physiological maturity. The factorial combination of two plant populations (2.4 and 4.8 plants m) and two levels of nitrogen supply (0 and 5 g N m) were the sources of variation for NW and light profiles. Before the onset of nitrogen accumulation in grain, the pattern of NW was similar to that described for other species and it was related to the distribution of light in the canopy. Important changes in the profile of NW occurred during grain filling that were unrelated to the light regime. Nitrogen was mobilised from leaves in all positions in the canopy and the rate of NW change was greater in leaves closer to the grain, which were also the leaves where nitrogen was more concentrated. It is concluded that the physiological mechanisms involved in determining the distribution of leaf nitrogen in vegetative canopies do not apply to sunflower during grain filling.
在许多物种的营养冠层中，叶片氮浓度（NW）的垂直梯度与光分布曲线平行，使得实际的氮分配接近冠层光合作用的最佳模式。本文评估了以下假设：一个强大的氮库，即正在生长的籽粒，会影响通常描述的营养冠层叶片氮分布模式。对向日葵（Helianthus annuus L.）作物从开花到生理成熟阶段的光和NW曲线进行了表征。两个植株密度（2.4株/m和4.8株/m）和两个氮供应水平（0和5 g N/m）的析因组合是NW和光曲线变化的来源。在籽粒开始积累氮之前，NW模式与其他物种描述的模式相似，并且与冠层中的光分布有关。在籽粒灌浆期间，NW曲线发生了重要变化，这些变化与光照条件无关。冠层中各个位置的叶片都有氮素被转运出来，靠近籽粒的叶片中NW变化速率更大，而这些叶片也是氮素更集中的叶片。得出的结论是，决定营养冠层叶片氮分布的生理机制不适用于籽粒灌浆期的向日葵。
