Effects of nitrogen fertilisation: on morphological and physiological responses

This study evaluates the influence of different forms of nitrogen (NO¿¿, NH¿¿, or a combination of both) on the tomato's response to cadmium stress. The results show that ammonium reduces growth due to its effects on pH, mineral nutrition, photosynthesis, and gas exchange. However, in the presence of cadmium, plants fertilized with ammonium exhibit greater tolerance than those receiving only nitrate, with less pronounced photoinhibition of photosystem II. Cadmium disrupts nitrate uptake and assimilation by inhibiting the NR, NiR, and GS enzymes, whereas Fd-GOGAT activity is better preserved under ammonium nutrition. Conversely, NADH-GDH is strongly stimulated, compensating for the inhibition of the GS/GOGAT pathway and promoting ammonium detoxification as well as the synthesis of glutamate and proline. The high accumulation of proline, particularly under ammonium nutrition, is associated with greater tolerance to cadmium. Finally, the removal of cadmium allows for a more rapid resumption of growth in ammonium-fed plants, confirming the protective effect of this form of nitrogen.