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<p>Purpose: Alternate wetting and drying (AWD) mode can increase nitrous oxide (N<sub>2</sub>O) emissions compared to continuous flooding irrigation (CF). However, existing studies predominantly measured the emission flux, which is insufficient to elucidate the effects of AWD mode on N<sub>2</sub>O production and nitrogen transformation processes across soil profiles. Methods: Two rhizobox experiments employing in situ multi-layer sampling devices were conducted to simultaneously monitor N<sub>2</sub>O concentrations, soil physicochemical properties and nitrogen-cycling functional genes at the three soil depths (0–10, 10–20 and 20–30&#xa0;cm) throughout the entire growth stage of double-cropping rice (<i>Oryza sativa</i> L.). Results: Compared to CF mode, AWD mode significantly enhanced the cumulative N<sub>2</sub>O emissions (by 10.48 times for late-season rice and 14.66 times in early-season rice) and the abundances of elevated N-cycling functional gene. The wetting-drying cycles in AWD mode reduced soil water content while increasing oxygen content, thereby stimulating both soil nitrification and nitrate leaching into the 10–20&#xa0;cm soil layer. Subsequent re-flooding triggered anaerobic conditions, markedly amplifying denitrification activity, resulting in peak N<sub>2</sub>O concentration (315.74-352.37 µL·L<sup>− 1</sup>) and emission flux (360.60–380.34&#xa0;µg·m<sup>− 2</sup>·h<sup>− 1</sup>) in the 10–20&#xa0;cm soil layer during milking stage. The partial least squares path model (PLS-PM) revealed stronger correlations between soil N<sub>2</sub>O concentration and denitrification genes (particularly <i>nirK</i>, <i>r</i> = 0.61, <i>p</i> &lt; 0.01) than with emission flux in AWD mode. Water layer depth had a stronger effect on emission fluxes (direct effect = -0.57) than soil nitrogen metabolic activities (direct effect = -0.37 and 0.31) in AWD mode. Conclusions: Therefore, strategic regulation of water layer depth may mitigate the N<sub>2</sub>O emission without considering denitrification activity in the 10–20&#xa0;cm layer in AWD mode.</p>

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N2O Concentration and Nitrogen-Cycling Functional Genes as Affected by Alternate Wetting and Drying Irrigation

  • 期刊论文

  • 发表日期：

    2025年8月7日

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  • Jiafa Wu,
  • Shuang Wu,
  • Wei Xiao,
  • Han Long,
  • Yang Wu,
  • Fusheng Li

摘要

Purpose: Alternate wetting and drying (AWD) mode can increase nitrous oxide (N2O) emissions compared to continuous flooding irrigation (CF). However, existing studies predominantly measured the emission flux, which is insufficient to elucidate the effects of AWD mode on N2O production and nitrogen transformation processes across soil profiles. Methods: Two rhizobox experiments employing in situ multi-layer sampling devices were conducted to simultaneously monitor N2O concentrations, soil physicochemical properties and nitrogen-cycling functional genes at the three soil depths (0–10, 10–20 and 20–30 cm) throughout the entire growth stage of double-cropping rice (Oryza sativa L.). Results: Compared to CF mode, AWD mode significantly enhanced the cumulative N2O emissions (by 10.48 times for late-season rice and 14.66 times in early-season rice) and the abundances of elevated N-cycling functional gene. The wetting-drying cycles in AWD mode reduced soil water content while increasing oxygen content, thereby stimulating both soil nitrification and nitrate leaching into the 10–20 cm soil layer. Subsequent re-flooding triggered anaerobic conditions, markedly amplifying denitrification activity, resulting in peak N2O concentration (315.74-352.37 µL·L− 1) and emission flux (360.60–380.34 µg·m− 2·h− 1) in the 10–20 cm soil layer during milking stage. The partial least squares path model (PLS-PM) revealed stronger correlations between soil N2O concentration and denitrification genes (particularly nirK, r = 0.61, p < 0.01) than with emission flux in AWD mode. Water layer depth had a stronger effect on emission fluxes (direct effect = -0.57) than soil nitrogen metabolic activities (direct effect = -0.37 and 0.31) in AWD mode. Conclusions: Therefore, strategic regulation of water layer depth may mitigate the N2O emission without considering denitrification activity in the 10–20 cm layer in AWD mode.