Broadley M R, Escobar-Gutiérrez A J, Burns A, Burns I G
1 Department of Soil & Environment Sciences, Horticulture Research International, Wellesbourne, Warwick CV35 9EF, UK.
New Phytol. 2000 Sep;147(3):519-526. doi: 10.1046/j.1469-8137.2000.00715.x.
Relationships between nitrogen (N) content and growth are routinely measured in plants. This study determined the effects of N on the separate morphological and physiological components of plant growth, to assess how N-limited growth is effected through these components. Lettuce (Lactuca sativa) plants were grown hydroponically under contrasting N-supply regimes, with the external N supply either maintained continuously throughout the period of study, or withdrawn for up to 14 d. Richards' growth functions, selected using an objective curve-fitting technique, accounted for 99.0 and 99.1% of the variation in plant dry weight for control and N-limited plants respectively. Sublinear relationships occurred between N and relative growth rates under restricted N-supply conditions, consistent with previous observations. There were effects of treatment on morphological and physiological components of growth. Leaf weight ratio increased over time in control plants and decreased in N- limited plants. Shoot:root ratio followed a similar pattern. On a whole-plant basis, assimilation of carbon decreased in N-limited plants, a response paralleled by differences in stomatal conductance between treatments. Changes in C assimilation, expressed as a function of stomatal conductance to water vapour, suggest that the effects of N limitation on growth did not result directly from a lack of photosynthetic enzymes. Relationships between plant N content and components of growth will depend on the availability of different N pools for remobilization and use within the plant.
植物中氮（N）含量与生长之间的关系常被测定。本研究确定了氮对植物生长的形态和生理组成部分的单独影响，以评估氮限制生长是如何通过这些组成部分产生影响的。生菜（Lactuca sativa）植株在不同的氮供应模式下进行水培生长，外部氮供应在整个研究期间要么持续维持，要么停止供应长达14天。使用客观曲线拟合技术选择的理查兹生长函数分别解释了对照植株和氮限制植株干重变化的99.0%和99.1%。在氮供应受限的条件下，氮与相对生长速率之间呈现亚线性关系，这与之前的观察结果一致。处理对生长的形态和生理组成部分有影响。对照植株的叶重比随时间增加，而氮限制植株的叶重比下降。地上部与地下部的比值也呈现类似模式。从整株植物来看，氮限制植株的碳同化作用降低，这种反应与处理间气孔导度的差异相平行。以对水蒸气的气孔导度为函数表示的碳同化变化表明，氮限制对生长的影响并非直接源于光合酶的缺乏。植物氮含量与生长组成部分之间的关系将取决于植物体内不同氮库用于再利用和利用的可用性。
