Plant ammonium sensitivity is associated with the external pH adaptation, repertoire of nitrogen transporters, and nitrogen requirement.

Abstract

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. This study conducts a meta-analysis of 50 plant species and presents a new classification method based on the comparison of fresh biomass obtained under ammonium and nitrate nutrition. The classification uses the natural logarithm of 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 counteracting role of ammonium toxicity in species with a higher abundance of genes encoding NRT2-type proteins and fewer of the AMT2-type proteins. Additionally, the study confirms the reliability of the phytohormone balance and methylglyoxal content as indicators for anticipating ammonium toxicity.