BUSCADOR RECOLECTA

Modern crops exhibit diverse sensitivities to ammonium as the primary nitrogen source, influenced by environmental factors such as external pH and nutrient availability. Despite its significance, there is currently no systematic classification of plant species based on their ammonium sensitivity. We conducted a meta-analysis of 50 plant species and present a new classification method based on the comparison of fresh biomass obtained under ammonium and nitrate nutrition. The classification uses the natural logarithm of the biomass ratio as the size effect indicator of ammonium sensitivity. This numerical parameter is associated with critical factors for nitrogen demand and form preference, such as Ellenberg indicators and the repertoire of nitrogen transporters for ammonium and nitrate uptake. Finally, a comparative analysis of the developmental and metabolic responses, including hormonal balance, is conducted in two species with divergent ammonium sensitivity values in the classification. Results indicate that nitrate has a key role in counteracting ammonium toxicity in species with a higher abundance of genes encoding NRT2-type proteins and fewer of those encoding the AMT2-type proteins. Additionally, the study demonstrates the reliability of the phytohormone balance and methylglyoxal content as indicators for anticipating ammonium toxicity. This study emphasizes the importance of ecophysiological requirements and the repertoire of nitrogen transporters in understanding plant sensitivity to ammonium, and enhances our knowledge of plant nitrogen nutrition., MR-M received funding from a PhD fellowship through the Public University of Navarra. IA was supported by an MCIN RyC Programme MCIN/AEI/10.13039/501100011033 and by the 'European Union Next Generation EU/PRTR' under grant no. RYC2021-032345-I. This work was supported by the AEI under grant no. PID2019-107463RJ-I00/AEI/10.13039/501100011033, and the Regional Research and Development Programme of the Government of Navarre (calls 2019 and 2020, projects NitroHealthy2, PC068, and HORTA0,0; PC106-107). Open Access funding was provided by Universidad Publica de Navarra.

The use of ammonium-based fertilizers together with nitrification inhibitors could be a possible alternative to limit N losses, currently derived from nitrate enrichment of soil and water, which are detrimental to the environment. However, prolonged application of ammonium as the main N source can result in development disorders in most plants, commonly referred to as 'ammonium syndrome'. Even if the origin of plants' sensitivity to ammonium is not fully understood, important biological components related to this syndrome have been unraveled over the last years. These components could constitute key targets to develop tools to counteract ammonium toxicity in crops. Thus, this chapter describes structural and metabolic components of root cells related to plant sensitivity to ammonium and how they could be key targets to combat ammonium toxicity by the use of fortification elements, such as silicon. Si is a beneficial element for plants as it increases their resistance to several stresses, including ammonium. New experimental evidences show specific role of Si in alleviating ammonium toxicity of several crops., MR was supported by a UPNa PhD Scholarship. IA was supported by a MCIN RyC Programme MCIN/AEI/10.13039/501100011033 and by 'European Union Next Generation EU/PRTR' under grant Nº. RYC2021-032345-I. This work was supported by the AEI under grant Nº. PID2019-107463RJ-I00 AEI/10.13039/501100011033