Walker R L, Burns I G, Moorby J
Horticulture Research International, Wellesbourne, Warwick CV35 9EF, UK.
J Exp Bot. 2001 Feb;52(355):309-17.
This paper investigates the effects of uptake of nitrate and the availability of internal N reserves on growth rate in times of restricted supply, and examines the extent to which the response is mediated by the different pools of N (nitrate N, organic N and total N) in the plant. Hydroponic experiments were carried out with young lettuce plants (Lactuca sativa L.) to compare responses to either an interruption in external N supply or the imposition of different relative N addition rate (RAR) treatments. The resulting relationships between whole plant relative growth rate (RGR) and N concentration varied between linear and curvilinear (or possibly bi-linear) forms depending on the treatment conditions. The relationship was curvilinear when the external N supply was interrupted, but linear when N was supplied by either RAR methods or as a supra-optimal external N supply. These differences resulted from the ability of the plant to use external sources of N more readily than their internal N reserves. These results show that when sub-optimal sources of external N were available, RGR was maintained at a rate which was dependent on the rate of nitrate uptake by the roots. Newly acquired N was channelled directly to the sites of highest demand, where it was assimilated rapidly. As a result, nitrate only tended to accumulate in plant tissues when its supply was essentially adequate. By comparison, plants forced to rely solely on their internal reserves were never able to mobilize and redistribute N between tissues quickly enough to prevent reductions in growth rate as their tissue N reserves declined. Evidence is presented to show that the rate of remobilization of N depends on the size and type of the N pools within the plant, and that changes in their rates of remobilization and/or transfer between pools are the main factors influencing the form of the relationship between RGR and N concentration.
本文研究了硝酸盐吸收和植物体内氮储备的可用性对供应受限时期生长速率的影响，并考察了植物中不同氮库（硝酸盐氮、有机氮和总氮）介导这种响应的程度。使用生菜幼苗（Lactuca sativa L.）进行水培实验，以比较对外部氮供应中断或施加不同相对氮添加率（RAR）处理的响应。根据处理条件，整株植物相对生长速率（RGR）与氮浓度之间的关系在线性和曲线（或可能是双线性）形式之间变化。当外部氮供应中断时，关系呈曲线形，但当通过RAR方法或作为超最佳外部氮供应提供氮时，关系呈线性。这些差异源于植物比其内部氮储备更易利用外部氮源的能力。这些结果表明，当有次优的外部氮源时，RGR维持在一个取决于根系硝酸盐吸收速率的水平。新获取的氮直接输送到需求最高的部位，并在那里迅速被同化。因此，只有当硝酸盐供应基本充足时，它才会在植物组织中积累。相比之下，被迫仅依靠其内部储备的植物，随着其组织氮储备下降，永远无法足够快地在组织间调动和重新分配氮以防止生长速率降低。有证据表明，氮的再调动速率取决于植物体内氮库的大小和类型，并且它们在库之间的再调动和/或转移速率的变化是影响RGR与氮浓度之间关系形式的主要因素。
