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A fully mechanistic dynamical model for plant nitrate uptake is presented. Based on physiological and regulatory pathways and based on physical laws, we form a dynamic system mathematically described by seven differential equations. The model evidences the presence of a short‐term positive feedback on the high‐affinity nitrate uptake, triggered by the presence of nitrate around the roots, which induces its intaking. In the long run, this positive feedback is overridden by two long‐term negative feedback loops which drastically reduces the nitrate uptake capacity. These two negative feedbacks are due to the generation of ammonium and amino acids, respectively, and inhibit the synthesis and the activity of high‐affinity nitrate transporters. This model faithfully predicts the typical spiking behavior of the nitrate uptake, in which an initial strong increase of nitrate absorption capacity is followed by a drop, which regulates the absorption down to the initial value. The model outcome was compared with experimental data and they fit quite nicely. The model predicts that after the initial exposure of the roots with nitrate, the absorption of the anion strongly increases and that, on the contrary, the intensity of the absorption is limited in presence of ammonium around the roots. [ABSTRACT FROM AUTHOR]

The low bioavailability of nutrients, especially nitrogen (N) and phosphorus (P), is one of the most limiting factors for crop production. In this study, under N- and P-free nutrient solution (-N-P), nodulating white lupin plants developed some nodules and analogous cluster root structures characterized by different morphological, physiological, and molecular responses than those observed upon single nutrient deficiency (strong acidification of external media, a better nutritional status than -N+P and +N-P plants). The multi-elemental analysis highlighted that the concentrations of nutrients in white lupin plants were mainly affected by P availability. Gene-expression analyses provided evidence of interconnections between N and P nutritional pathways that are active to promote N and P balance in plants. The root exudome was mainly characterized by N availability in nutrient solution, and, in particular, the absence of N and P in the nutrient solution triggered a high release of phenolic compounds, nucleosides monophosphate and saponines by roots. These morphological, physiological, and molecular responses result from a close interplay between N and P nutritional pathways. They contribute to the good development of nodulating white lupin plants when grown on N- and P-free media. This study provides evidence that limited N and P availability in the nutrient solution can promote white lupin-Bradyrhizobium symbiosis, which is favourable for the sustainability of legume production. [ABSTRACT FROM AUTHOR]

The simultaneous presence of different N‐forms in the rhizosphere leads to beneficial effects on nitrogen (N) nutrition in plants. Although widely used as fertilizers, the occurrence of cross connection between urea and ammonium nutrition has been scarcely studied in plants. Maize fed with a mixture of urea and ammonium displayed a better N‐uptake efficiency than ammonium‐ or urea‐fed plants (Buoso et al., Plant Physiol Biochem, 2021a; 162: 613–623). Through multiomic approaches, we provide the molecular characterization of maize response to urea and ammonium nutrition. Several transporters and enzymes involved in N‐nutrition were upregulated by all three N‐treatments (urea, ammonium, or urea and ammonium). Already after 1 day of treatment, the availability of different N‐forms induced specific transcriptomic and metabolomic responses. The combination of urea and ammonium induced a prompt assimilation of N, characterized by high levels of some amino acids in shoots. Moreover, ZmAMT1.1a, ZmGLN1;2, ZmGLN1;5, ZmGOT1, and ZmGOT3, as well transcripts involved in glycolysis‐TCA cycle were induced in roots by urea and ammonium mixture. Depending on N‐form, even changes in the composition of phytohormones were observed in maize. This study paves the way to formulate guidelines for the optimization of N fertilization to improve N‐use efficiency in maize and therefore limit N‐losses in the environment. [ABSTRACT FROM AUTHOR]