Nitrogen fertilizer is a key input for ensuring high crop yields, but excessive nitrogen application is widespread in China’s agricultural production. This not only increases production costs but also causes a series of environmental problems, including water eutrophication, soil acidification, and increased greenhouse gas emissions. Therefore, improving crop nitrogen use efficiency (NUE) has become one of the core goals of sustainable agriculture. Although existing studies have indicated differences in NUE among flue-cured tobacco cultivars, the underlying physiological mechanisms remain unclear. In particular, how nitrogen allocation among different functional fractions within the plant regulates these differences has long lacked systematic analysis.
The flue-cured tobacco cultivars Hongda and K326 are widely used in production. The former is known for its superior leaf quality, while the latter is known for its strong stress resistance. The two cultivars also show clear divergence in NUE, making them ideal materials for studying the mechanisms of nitrogen efficiency.
Against this background, the team led by Zhengxiong ZHAO and Shaoming LI at Yunnan Agricultural University published a research paper titled “Nitrogen allocation to biochemical fractions shapes functional traits and N use efficiency in tobacco cultivars” in ENGINEERING Agriculture (DOI: 10.15302/J-FASE-2026681). The study systematically explored the allocation patterns of nitrogen among different biochemical fractions, revealed the intrinsic mechanisms underlying cultivar differences in biomass accumulation and NUE in flue-cured tobacco, and provided an important physiological basis for breeding nitrogen-efficient crop cultivars and optimizing nitrogen management.
Through a pot experiment, the research team set three nitrogen application levels (0, 4, and 8 g pure N per plant) and collected samples every 25 days throughout the growth period of the two cultivars. This was done to reveal how nitrogen allocation to specific functional fractions in the previous period directly affects biomass and nitrogen accumulation rates in the subsequent period. At the same time, plant nitrogen was finely divided into four solubility fractions: water-soluble nitrogen, SDS-soluble nitrogen, SDS-insoluble nitrogen, and non-protein nitrogen. These were further integrated into four functional categories: photosynthetic nitrogen, respiratory nitrogen, structural nitrogen, and storage nitrogen. Through stepwise regression analysis, the team found that the key nitrogen fractions affecting biomass and nitrogen accumulation differed markedly under different nitrogen application levels.
Under nitrogen-deficient conditions, the allocation proportions of photosynthetic nitrogen and respiratory nitrogen were crucial for maintaining continued plant growth. Under moderate nitrogen input, structural nitrogen (SDS-insoluble nitrogen) in stems became the dominant factor promoting leaf biomass accumulation. When nitrogen application reached 8 g per plant, water-soluble nitrogen in roots became the main contributor to increasing total biomass. Notably, under low and moderate nitrogen conditions, the high-NUE cultivar Hongda consistently allocated more nitrogen preferentially to functional fractions related to the photosynthetic apparatus and respiratory metabolism, rather than to inert storage pools. This “active investment” allocation strategy enabled it to accumulate more biomass and nitrogen than K326 under the same nitrogen application rate.
The value of this study lies in its functional and quantitative resolution of the within-plant nitrogen allocation process that has traditionally been regarded as a “black box”, breaking through the previous limitation of focusing only on total nitrogen uptake. The key physiological indicators identified in the study, such as photosynthetic nitrogen and structural nitrogen, can serve directly as selection targets for breeding high-NUE crops. At the same time, the study revealed that the optimal nitrogen allocation strategy differs significantly under different nitrogen application levels, meaning that precision fertilization strategies need to be customized according to cultivar-specific nitrogen allocation characteristics. For high-NUE cultivars such as Hongda, moderate nitrogen reduction may not only avoid substantial yield loss but may also promote more efficient use of endogenous nitrogen.
Although this study focused on flue-cured tobacco, functional nitrogen pools such as photosynthetic nitrogen and structural nitrogen are ubiquitous in major crops such as maize, rice, and wheat, and their biological functions are highly conserved. Therefore, the regulatory logic of nitrogen allocation revealed in this study has significant cross-species reference value. If future research further clarifies the commonalities and specificities of these mechanisms across different crops, it will provide a more solid theoretical foundation for breeding “low-fertilizer, high-yield” green cultivars and constructing environmentally friendly fertilization systems. This study also provides a clear physiological model for shifting breeding thinking from “pursuing total nitrogen uptake” to “optimizing nitrogen allocation”.
DOI: 10.15302/J-FASE-2026681