Plant Gene and Trait 2025, Vol.16, No.3, 133-141 http://genbreedpublisher.com/index.php/pgt 134 2 Nitrogen Uptake and Utilization in Tomato Plants 2.1 Mechanisms of nitrogen absorption and transport Tomatoes mainly absorb nitrogen from the soil through their root systems, mainly ammonium nitrogen and nitrate nitrogen. Whether the root system can efficiently absorb this nitrogen is related to the microorganisms around the roots, the amount of organic matter in the soil, and the type of nitrogen. Studies have found that if some beneficial bacteria, such as Bacillus pumilus, are added to the soil, it can help tomatoes absorb nitrogen better, and at the same time, it can also make the nitrogen in the soil transform faster and have a better absorption effect (Masood et al., 2020). In addition, soil additives such as biochar and humic acid can also improve soil quality, make roots more active and enhance their nitrogen absorption capacity (Qin et al., 2023; Zhang et al., 2023). The nitrogen absorbed by the plant is transported to parts such as leaves, stems and fruits through the plant’s conducting tissues (such as xylem and phloem) to meet the needs at different stages (Liu et al., 2020; Wang et al., 2025). 2.2 Role of nitrogen in vegetative and reproductive development Nitrogen is of great significance to tomatoes. It affects the size of leaves, the intensity of photosynthesis, the amount of dry matter accumulated by the plants, and ultimately determines the yield. If nitrogen is supplied just right, it will make the leaves grow faster, be greener in color and have a higher photosynthetic efficiency (Zhang et al., 2021a; Zhang et al., 2021b). When tomatoes start to flower and bear fruit, the demand for nitrogen will increase further. Sufficient nitrogen is conducive to more flowering and fruiting, and the yield will also increase accordingly (Wang et al., 2024a; Wang et al., 2025). However, if too much nitrogen is applied, not only will the output not continue to increase, but also the utilization rate of nitrogen will decrease, causing waste and even polluting the environment (Liu et al., 2020; Wang et al., 2025). Applying nitrogen fertilizer in stages can better meet the needs of tomatoes at each stage, improve the utilization rate of nitrogen, and make the yield more stable (Wang et al., 2025). 2.3 Nitrogen metabolism specific to indeterminate growth types Indeterminate tomatoes keep growing, flowering and bearing fruit. Their demand for nitrogen is phased and dynamically changing. During the seedling stage, it mainly relies on the original nitrogen in the soil. When it comes to flowering and fruit expansion, additional nitrogen needs to be supplemented externally (Wang et al., 2025). If there is not enough nitrogen at this time, tomatoes will recycle the nitrogen in their bodies through the mechanism of “autophagy”, for example, through the ATg6-dependent pathway to improve their adaptability to a low-nitrogen environment (Figure 1) (Cao et al., 2022). Some research has also found that grafting rootstocks with high nitrogen efficiency can help tomatoes absorb nitrogen better, increase the activity of key enzymes, make better use of nitrogen, and improve yield and quality accordingly (Zhang et al., 2021a; Zhang et al., 2021b). In addition, the forms of nitrogen (such as the ratio of ammonium to nitrate) and the environmental conditions around the roots, such as the distribution of soil salinity, also affect the effect of nitrogen absorption and utilization in tomatoes (Wang et al., 2024a; Wang et al., 2024b). 3 Limitations of Single-Dose Nitrogen Application 3.1 Risk of nitrogen loss: leaching and volatilization If nitrogen fertilizer is applied all at once, it is very likely to cause waste of fertilizer. Especially in cases of heavy rainfall or frequent irrigation, nitrogen will be washed by water to the deep soil, and the roots cannot absorb it (Nie et al., 2021; Sun et al., 2023). In addition, nitrogen may also volatilize and escape into the air, not only reducing the fertilizer efficiency but also polluting the environment. 3.2 Nutrient imbalance and excess vegetative growth Applying a large amount of nitrogen at one time may also cause tomatoes to grow too fast, with only leaves, no flowers or no fruits (Nie et al., 2021; Wang et al., 2025). In fact, tomatoes do not have a high demand for nitrogen during the seedling stage. If too much nitrogen is applied at this time, it will not only be ineffective but also easily cause the plants to grow excessively, affecting the subsequent fruiting and yield (Zhou et al., 2020; Wang et al., 2025).
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