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<p>Nitrogen (N) is an essential macronutrient that supports plant growth, yield, and metabolism, yet excessive agricultural use poses serious environmental risks. In tomato, improving nitrogen-use efficiency requires a deeper understanding of physiological responses to N limitation. This controlled-environment experiment with the plants grown in pots, conducted under greenhouse conditions (25/18°C, 55% R.H) provides mechanistic insights into how N limitation alters tomato yield and fruit quality independent of variable field conditions. Such controlled studies serve as a guiding reference for optimizing fertilization strategies and selecting genotypes with improved N use for regions with limited N availability. We used two N levels optimal (4 mM) and low (0.8 mM) and found that N deficiency markedly reduced vegetative growth and fruit yield, with declines in SPAD value, plant height, shoot and root biomass, and total yield by 38.6%, 36.5%, 28.7%, 29.3%, and 62.5%, respectively. Fruit quality traits such as firmness, total soluble sugars, starch, total free amino acids, and protein significantly decreased by 40.5%, 37.8%, 41.8%, 23.9%, and 10.2%, respectively. In contrast, nutritional compounds, including vitamin C, carotenoids, and lycopene significantly increased by 188.7%, 41.3%, and 38.2%, respectively. Enzymatic activities of glutamine synthetase (GS) and glutamate synthase (GOGAT) decreased by 38.8% and 72.2%. At the same time, expression of key genes including <i>PHOSPHOMANNOMUTASE (PMM)</i>,<i> GUANOSINE MONOPHOSPHATE SYNTHASE (GMP)</i>,<i> GDP-MANNOSE 3</i>,<i>5-EPIMERASE (GME)</i>,<i> GDP-L-GALACTOSE PHOSPHORYLASE (GGP)</i>,<i> VITAMIN C DEFECTIVE 4 (VTC4)</i>,<i> GLUTAMATE DEHYDROGENASE (GDH)</i>, and LACTATE DEHYDROGENASE (<i>LDH</i>), in the L-galactose ascorbate biosynthesis pathway were significantly upregulated. These findings highlight a metabolic reprogramming under N stress that shifts resources from growth to antioxidant accumulation. Despite yield reduction, N deficiency enhances fruit nutritional value and activates adaptive pathways. The findings elucidate the physiological and biochemical adjustments of tomato to N limitation and provide a theoretical basis for breeding cultivars with improved N adaptability and enhanced antioxidant potential, particularly suited for low-input and environmentally sensitive production regions.</p>

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Physiological and Metabolic Responses to Nitrogen Deficiency Reveal Trade-offs between Yield and Quality in Tomato

  • 期刊论文

  • 发表日期：

    2025年12月23日

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  • Andrew Nasa Thompson,
  • Mahmood Ul Hassan,
  • Yongqi Wang,
  • Xionggao Shi,
  • Chandni Iqbal,
  • Yanting Zhong,
  • Xiaoqiang Jiao,
  • Xuexian Li

摘要

Nitrogen (N) is an essential macronutrient that supports plant growth, yield, and metabolism, yet excessive agricultural use poses serious environmental risks. In tomato, improving nitrogen-use efficiency requires a deeper understanding of physiological responses to N limitation. This controlled-environment experiment with the plants grown in pots, conducted under greenhouse conditions (25/18°C, 55% R.H) provides mechanistic insights into how N limitation alters tomato yield and fruit quality independent of variable field conditions. Such controlled studies serve as a guiding reference for optimizing fertilization strategies and selecting genotypes with improved N use for regions with limited N availability. We used two N levels optimal (4 mM) and low (0.8 mM) and found that N deficiency markedly reduced vegetative growth and fruit yield, with declines in SPAD value, plant height, shoot and root biomass, and total yield by 38.6%, 36.5%, 28.7%, 29.3%, and 62.5%, respectively. Fruit quality traits such as firmness, total soluble sugars, starch, total free amino acids, and protein significantly decreased by 40.5%, 37.8%, 41.8%, 23.9%, and 10.2%, respectively. In contrast, nutritional compounds, including vitamin C, carotenoids, and lycopene significantly increased by 188.7%, 41.3%, and 38.2%, respectively. Enzymatic activities of glutamine synthetase (GS) and glutamate synthase (GOGAT) decreased by 38.8% and 72.2%. At the same time, expression of key genes including PHOSPHOMANNOMUTASE (PMM), GUANOSINE MONOPHOSPHATE SYNTHASE (GMP), GDP-MANNOSE 3,5-EPIMERASE (GME), GDP-L-GALACTOSE PHOSPHORYLASE (GGP), VITAMIN C DEFECTIVE 4 (VTC4), GLUTAMATE DEHYDROGENASE (GDH), and LACTATE DEHYDROGENASE (LDH), in the L-galactose ascorbate biosynthesis pathway were significantly upregulated. These findings highlight a metabolic reprogramming under N stress that shifts resources from growth to antioxidant accumulation. Despite yield reduction, N deficiency enhances fruit nutritional value and activates adaptive pathways. The findings elucidate the physiological and biochemical adjustments of tomato to N limitation and provide a theoretical basis for breeding cultivars with improved N adaptability and enhanced antioxidant potential, particularly suited for low-input and environmentally sensitive production regions.