Departamento de Ecología, Facultad de Ciencias, Universidad de Alcalá, ctra N-II 33,500 Alcalá de Henares, 28871 Madrid, Spain.
Tree Physiol. 2010 Feb;30(2):257-63. doi: 10.1093/treephys/tpp115. Epub 2009 Dec 18.
The relative contribution of nitrogen (N) reserves from seeds or uptake by the roots to the growth and N content of young seedlings has received little attention. In this study, we investigated the contribution of N from the acorn or uptake by the roots to the N content of holm oak (Quercus ilex L.) seedlings and determined if remobilization of acorn N was affected by nutrient availability in the growing media. Q. ilex seedlings were cultivated for 3 months, until the end of the second shoot flush of growth, with three N fertilization rates: 8.6 mM N, 1.4 mM N or no fertilization. Fertilizer N was enriched in (15)N. Between 62 and 75% of the N contained in high and low fertilized seedlings, respectively, at the end of the second flush of growth was derived from the acorn. However, the dependence on acorn N was greater during the early root growth and first shoot flush of growth and decreased during the second shoot flush of growth, with root uptake contributing 32-54% of plant new N in this latter developmental stage in high and low fertilized plants, respectively. Fertilization rate did not affect the amount of N taken up during the earliest developmental stages, but it increased it during the second shoot flush of growth. Fertilization increased the mass of the shoot segment formed during the second shoot flush of growth and reduced the root mass, with no effect on whole plant growth. Remobilization of acorn N was faster in unfertilized plants than in fertilized plants. It is concluded that the holm oak seedlings depend greatly upon acorn N until the end of the second shoot flush of growth, that significant root N uptake starts at the beginning of the second shoot flush of growth and that acorn N remobilization is a plastic process that is accelerated under extremely low substratum nutrient content.
橡子或根系吸收的氮（N）储备对幼苗生长和 N 含量的相对贡献一直受到关注。在这项研究中，我们研究了橡子中的 N 对欧洲栓皮栎（Quercus ilex L.）幼苗 N 含量的贡献，并确定了在生长介质中养分可用性是否会影响橡子 N 的再利用。Q. ilex 幼苗在三种 N 施肥率下培养了 3 个月，直到第二次生长高峰期结束：8.6 mM N、1.4 mM N 或不施肥。肥料 N 用 (15)N 进行了富集。在第二次生长高峰期结束时，高和低施肥的幼苗中分别有 62-75%的 N 来自橡子。然而，在早期根系生长和第一次生长高峰期，对橡子 N 的依赖程度更大，在高和低施肥的植物中，根系吸收分别在这一后期发育阶段为植物新 N 的 32-54%。施肥率不会影响早期发育阶段的 N 吸收量，但会在第二次生长高峰期增加。施肥增加了第二次生长高峰期形成的芽段的质量，减少了根的质量，但对整个植物的生长没有影响。与施肥植物相比，未施肥植物的橡子 N 再利用速度更快。研究结论为，欧洲栓皮栎幼苗在第二次生长高峰期结束前高度依赖橡子 N，在第二次生长高峰期开始时，根系吸收大量 N，橡子 N 再利用是一个可塑的过程，在极低的基质养分含量下会加速。
