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Background <p>Smooth vetch, a legume, is often used as a green manure in citrus orchards. However, the potential for competition or partitioning of nitrogen forms (NH<sub>4</sub><sup>+</sup> vs. NO<sub>3</sub><sup>−</sup>) between citrus and smooth vetch during overlapping phenological stages remains unclear, as do shifts in their uptake strategies.</p> Methods <p>An in situ <sup>15</sup>N isotope injection method was employed to investigate the changes in inorganic N uptake forms and their regulatory factors across different phenological stages under fertilization and no fertilization.</p> Results <p>Under fertilization, citrus plants preferentially took up NH<sub>4</sub><sup>+</sup> during shoot sprouting (CS) and fruit enlargement stage II (CYII), whereas smooth vetch plants preferentially took up NO<sub>3</sub><sup>−</sup>. Conversely, during fruit enlargement stages I (CYI) and III (CYIII), citrus preferentially took up NO<sub>3</sub><sup>−</sup>, whereas smooth vetch preferentially took up NH<sub>4</sub><sup>+</sup>. However, during the leaf expansion (CL) and flowering stages (CF), both citrus and smooth vetch showed a preference for NO<sub>3</sub><sup>−</sup>, suggesting that targeted nitrate–N fertilization may be beneficial during the CL stage. N uptake by citrus and smooth vetch was significantly positively correlated. Under no fertilization, during the CS, CF, CYI stages, both citrus and smooth vetch exhibited a preference for NH<sub>4</sub><sup>+</sup> uptake; in the subsequent phenological stages, both species shifted their preference towards NO<sub>3</sub><sup>−</sup> uptake, and N uptake by citrus and smooth vetch showed a significant negative correlation.</p> Conclusion <p>Nitrogen uptake strategies of citrus and smooth vetch vary dynamically across phenological stages, fertilization partially alleviated the nitrogen competition between the two species. These results reveal dynamic, stage-dependent nitrogen uptake strategies in citrus and smooth vetch, providing a scientific basis for timing and form-specific nitrogen fertilization in legume-covered citrus orchards. Future research should quantify nitrogen release during smooth vetch residue decomposition and its synchrony with citrus nitrogen demand.</p> Graphical Abstract <p></p>

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Nitrogen uptake strategies associated with phenological processes in a citrus orchard covered with smooth vetch

  • 期刊论文

  • 发表日期：

    2026年1月16日

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  • Xin Yang,
  • Jiajia Zhang,
  • Lei Lei,
  • Qiuling Zhou,
  • Yichen Li,
  • Hongbing Yang,
  • Lixiong Zeng,
  • Wenfa Xiao

摘要

Background

Smooth vetch, a legume, is often used as a green manure in citrus orchards. However, the potential for competition or partitioning of nitrogen forms (NH4+ vs. NO3−) between citrus and smooth vetch during overlapping phenological stages remains unclear, as do shifts in their uptake strategies.

Methods

An in situ 15N isotope injection method was employed to investigate the changes in inorganic N uptake forms and their regulatory factors across different phenological stages under fertilization and no fertilization.

Results

Under fertilization, citrus plants preferentially took up NH4+ during shoot sprouting (CS) and fruit enlargement stage II (CYII), whereas smooth vetch plants preferentially took up NO3−. Conversely, during fruit enlargement stages I (CYI) and III (CYIII), citrus preferentially took up NO3−, whereas smooth vetch preferentially took up NH4+. However, during the leaf expansion (CL) and flowering stages (CF), both citrus and smooth vetch showed a preference for NO3−, suggesting that targeted nitrate–N fertilization may be beneficial during the CL stage. N uptake by citrus and smooth vetch was significantly positively correlated. Under no fertilization, during the CS, CF, CYI stages, both citrus and smooth vetch exhibited a preference for NH4+ uptake; in the subsequent phenological stages, both species shifted their preference towards NO3− uptake, and N uptake by citrus and smooth vetch showed a significant negative correlation.

Conclusion

Nitrogen uptake strategies of citrus and smooth vetch vary dynamically across phenological stages, fertilization partially alleviated the nitrogen competition between the two species. These results reveal dynamic, stage-dependent nitrogen uptake strategies in citrus and smooth vetch, providing a scientific basis for timing and form-specific nitrogen fertilization in legume-covered citrus orchards. Future research should quantify nitrogen release during smooth vetch residue decomposition and its synchrony with citrus nitrogen demand.

Graphical Abstract