Nitrogen Forms and Silicon Sources in Tomato Plant Growth

Silicon (Si) is known to alleviate several abiotic stresses in plants, including ammonium (NH4+) toxicity. However, the availability of Si in the nutrient solution depends on factors such as the Si source and NH4+ concentration. This study evaluated the effects of two Si sources, stabilized silicic acid (ASiE) and potassium silicate (SiK), on Micro-Tom tomato grown under NH4+ toxicity. In the first experiment, plants were supplied with 0.0, 0.2, 0.4, 0.6, and 0.8 mmol L−1 Si from either SiK or ASiE. NH4+ toxicity was induced at a NO3−:NH4+ ratio of 3.8:11.2 mmol L−1. In the second experiment, plants received 0.0, 1.0, 2.0, and 2.5 mmol L−1 Si supplied as SiK. NH4+ toxicity was induced by 5.9 mmol L−1 NH4+, while 5.9 mmol L−1 NO3− was used as the control treatment. In the first experiment, Si supply did not increase shoot Si content or Si accumulation, and NH4+ toxicity was not alleviated. In contrast, in the second experiment, Si supply increased shoot Si content and Si accumulation, resulting in greater shoot and root dry weight under NH4+ toxicity. Similarly, plants supplied with NO3− also showed increased shoot and root dry weight in response to Si application. In conclusion, low concentrations of Si supplied as either SiK or ASiE were ineffective in alleviating NH4+ toxicity. However, SiK at 1.29 mmol L−1 Si alleviated NH4+ toxicity induced by 5.9 mmol L−1 NH4+ alone.