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<p>Nitrogen and calcium are essential nutrients that strongly influence plant photosynthesis, yield, and quality. However, their synergistic effects and underlying photosynthetic physiological mechanisms in pakchoi (<i>Brassica chinensis</i> L.) remain unclear. In this study, a pot experiment was conducted to systematically investigate the physiological responses of pakchoi under different nitrogen (0 and 0.4&#xa0;g N kg<sup>− 1</sup> dry soil) and Ca (0, 0.03, 0.06, 0.09&#xa0;g CaO kg<sup>− 1</sup> dry soil) application levels. The study analyzed differences in leaf photosynthetic performance, photosynthetic nitrogen allocation, chlorophyll fluorescence parameters, anatomical structure, and quality characteristics to elucidate the response patterns and internal mechanisms of nitrogen-calcium interactions. The results showed that combined nitrogen and calcium application (N0.4Ca0.06 treatment) maximized leaf area (1087 cm<sup>2</sup> plant<sup>− 1</sup>) and dry weight (8.02&#xa0;g plant<sup>− 1</sup>), while significantly increasing chlorophyll <i>a</i> and <i>b</i> contents by 19.8% and 37.5%, respectively. Further analysis indicated that nitrogen-calcium co-application enhanced photosynthetic capacity by increasing photosynthetic nitrogen content in both the carboxylation system (PNcb) and the light-harvesting system (PNcl) and by improving leaf anatomical traits, particularly the thickening of palisade tissue, which collectively promoted mesophyll conductance (gₘ). Additionally, nitrogen-calcium interaction markedly improved chlorophyll fluorescence parameters (Fv/Fm, ΦPSII, qP, ETR) and the activities of key carbon and nitrogen metabolism enzymes (NR, GS, GOGAT, SPS). Partial least squares path modeling (PLS-PM) revealed that nitrogen primarily influenced photosynthesis through regulating photosynthetic nitrogen allocation, while calcium mainly acted by modifying leaf structure. Quality analysis showed that although nitrogen application increased nitrate content, supplementary calcium effectively reduced nitrate accumulation while enhancing soluble sugar and vitamin C contents. In conclusion, coordinated nitrogen and calcium management enhances pakchoi photosynthesis by simultaneously improving biochemical capacity and CO<sub>2</sub> transport, thereby increasing yield and nutritional quality. This study provides a theoretical foundation for precise nutrient management to achieve yield and quality improvement in leafy vegetables represented by pakchoi.</p>

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Enhancing Yield and Quality of Pakchoi through Improved Photosynthetic and Enzyme Activity under Combined Nitrogen and Calcium Application

  • 期刊论文

  • 发表日期：

    2026年5月26日

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  • Li Ren,
  • Meng Li,
  • Chunyan Xu,
  • Yilun Wang,
  • Hehe Gu,
  • Shuntao Zhang,
  • Tongchao Wang,
  • Lantao Li

摘要

Nitrogen and calcium are essential nutrients that strongly influence plant photosynthesis, yield, and quality. However, their synergistic effects and underlying photosynthetic physiological mechanisms in pakchoi (Brassica chinensis L.) remain unclear. In this study, a pot experiment was conducted to systematically investigate the physiological responses of pakchoi under different nitrogen (0 and 0.4 g N kg− 1 dry soil) and Ca (0, 0.03, 0.06, 0.09 g CaO kg− 1 dry soil) application levels. The study analyzed differences in leaf photosynthetic performance, photosynthetic nitrogen allocation, chlorophyll fluorescence parameters, anatomical structure, and quality characteristics to elucidate the response patterns and internal mechanisms of nitrogen-calcium interactions. The results showed that combined nitrogen and calcium application (N0.4Ca0.06 treatment) maximized leaf area (1087 cm2 plant− 1) and dry weight (8.02 g plant− 1), while significantly increasing chlorophyll a and b contents by 19.8% and 37.5%, respectively. Further analysis indicated that nitrogen-calcium co-application enhanced photosynthetic capacity by increasing photosynthetic nitrogen content in both the carboxylation system (PNcb) and the light-harvesting system (PNcl) and by improving leaf anatomical traits, particularly the thickening of palisade tissue, which collectively promoted mesophyll conductance (gₘ). Additionally, nitrogen-calcium interaction markedly improved chlorophyll fluorescence parameters (Fv/Fm, ΦPSII, qP, ETR) and the activities of key carbon and nitrogen metabolism enzymes (NR, GS, GOGAT, SPS). Partial least squares path modeling (PLS-PM) revealed that nitrogen primarily influenced photosynthesis through regulating photosynthetic nitrogen allocation, while calcium mainly acted by modifying leaf structure. Quality analysis showed that although nitrogen application increased nitrate content, supplementary calcium effectively reduced nitrate accumulation while enhancing soluble sugar and vitamin C contents. In conclusion, coordinated nitrogen and calcium management enhances pakchoi photosynthesis by simultaneously improving biochemical capacity and CO2 transport, thereby increasing yield and nutritional quality. This study provides a theoretical foundation for precise nutrient management to achieve yield and quality improvement in leafy vegetables represented by pakchoi.