Abstract Epiphytic bromeliads are subjected to intermittent nutrient availability while at the same time having a small root system that absorb a small amount of nutrients. These bromeliads possess adaptations, such as a tank formation and a higher trichome density, that contribute to their acquisition of water and nutrients. However, little is known about the nitrogen metabolism in epiphytic tank bromeliads or how ammonium reaches the leaf apex before its assimilation, and nothing has been described about the functioning of the low- and high-affinity nitrogen transporters in epiphytic plants whose leaves play a key role in nutrient uptake. In this context, we conducted a controlled experiment with Guzmania monostachia to investigate its nutritional preference when nitrate, ammonium and urea are offered at the same time, its nitrogen assimilation along the leaf blade, and whether the high-affinity nitrogen transporters (NRT2.5, AMT1.2, DUR3) present the highest gene expressions under low nitrogen availability. Our results revealed that the leaf base was responsible for nitrogen absorption and ammonium production through urease and NR activities and showed an upregulation of the high-affinity transporters of nitrate and ammonium (NRT2.5, AMT1.2), together with the urea transporter genes (DUR3, aquaporin TIP2.1). On the other hand, the leaf apex presented remarkable characteristics relating to GS activity and showed the highest gene expression of low-affinity nitrate (NRT1.2) and ammonium (AMT3.1, aquaporin PIP1.2) transporters. These results suggest that nitrogen absorption and assimilation occurred in a single leaf in G. monostachia as its leaves played the role of a whole plant regarding nitrogen metabolism. The leaf base was essential in nitrogen absorption, nitrate reduction, and urea hydrolysis. In this leaf portion, the upregulation of the high-affinity transporters could ensure efficient nitrogen uptake even in low concentrations. In an epiphytic environment, with extremely limited nutrient availability, the bromeliad leaves seem to be the main organ that guarantees plant survival.

中文翻译：

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将叶子视为整株植物：在吸收叶面养分的植物中，氮代谢是如何发生的？

摘要 附生凤梨科植物具有间歇性的养分可用性，同时具有吸收少量养分的小根系。这些凤梨科植物具有适应性，例如水箱形成和更高的毛状体密度，这有助于它们获取水分和营养。然而，关于附生罐凤梨科植物中的氮代谢或铵如何在其同化之前到达叶尖知之甚少，并且没有任何关于附生植物中低亲和力和高亲和力氮转运蛋白的功能的描述，这些植物的叶子起着关键作用养分吸收中的作用。在这种情况下，我们对 Guzmania monostachia 进行了一项对照实验，以研究同时提供硝酸盐、铵和尿素时的营养偏好，它沿叶片的氮同化，以及高亲和力氮转运蛋白（NRT2.5、AMT1.2、DUR3）是否在低氮可用性下表现出最高的基因表达。我们的结果表明，叶基通过尿素酶和 NR 活性负责氮吸收和铵的产生，并显示出硝酸盐和铵的高亲和力转运蛋白（NRT2.5，AMT1.2）以及尿素转运蛋白基因的上调（DUR3，水通道蛋白 TIP2.1）。另一方面，叶尖呈现出与 GS 活性相关的显着特征，并显示出低亲和力硝酸盐 (NRT1.2) 和铵 (AMT3.1，水通道蛋白 PIP1.2) 转运蛋白的最高基因表达。这些结果表明氮吸收和同化发生在 G 的单叶中。monostachia 作为它的叶子在氮代谢方面起到了整株植物的作用。叶基对氮吸收、硝酸盐还原和尿素水解至关重要。在这个叶部分，高亲和力转运蛋白的上调可以确保即使在低浓度下也能有效吸收氮。在附生环境中，营养供应极其有限，凤梨科植物的叶子似乎是保证植物生存的主要器官。