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<p>Alkaline fly ash (FA) has potential as a soil amendment for acidic forest soils, leading to improved soil conditions and tree growth. Such improvements may be reflected in the stable isotope ratios of N (δ<sup>15</sup>N) and carbon (δ<sup>13</sup>C) in tree tissues, which serve as time-integrated indicators of N availability and photosynthetic gas exchange, respectively. This study examined δ<sup>15</sup>N and δ<sup>13</sup>C of needles from red pine (<i>Pinus densiflora</i> f. <i>aggregate</i> Nakai) saplings grown for 25 weeks in artificially acidified soils (pH 3.5) with and without FA. Sapling growth increments were measured, and both soil and needle samples were collected. Soil samples were assessed for pH, exchangeable cations, and mineral N concentrations. Needle samples were analyzed for δ<sup>13</sup>C, N concentration, δ<sup>15</sup>N, and cations concentrations. FA application significantly enhanced (<i>P</i> &lt; 0.001) tree growth by increasing soil pH (by &gt; 4.0 units) and Ca<sup>2+</sup> concentration (by over two-fold). FA also reduced soil NH<sub>4</sub><sup>+</sup> levels (<i>P</i> &lt; 0.001), accompanied by a corresponding increase in NO<sub>3</sub><sup>−</sup> concentration, which indirectly indicates enhanced nitrification. The increase in needle δ<sup>15</sup>N values (<i>P</i> &lt; 0.05), from 4.3–4.6‰ without FA to 5.4–5.7‰ with FA, further indirectly supported increased N availability and losses associated with nitrification. In contrast, needle δ<sup>13</sup>C values were unaffected by FA treatment, suggesting that stomatal conductance and carboxylation rate increased proportionally. Our findings demonstrate that FA can serve as a soil amendment for remediating acidic forest soils to improve tree growth by enhancing N cycling and alleviating soil acidity.</p>

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δ15N and δ13C of pine sapling needles as indicators of enhanced N cycling and ameliorated acidity by alkaline fly ash application in artificially acidified soils

  • 期刊论文

  • 发表日期：

    2025年12月11日

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  • Hyun-Jin Park,
  • Kwang-Seung Lee,
  • Nuri Baek,
  • Seo-Woo Park,
  • Eun-Seo Shin,
  • Jiyu Lee,
  • Woo-Jung Choi

摘要

Alkaline fly ash (FA) has potential as a soil amendment for acidic forest soils, leading to improved soil conditions and tree growth. Such improvements may be reflected in the stable isotope ratios of N (δ15N) and carbon (δ13C) in tree tissues, which serve as time-integrated indicators of N availability and photosynthetic gas exchange, respectively. This study examined δ15N and δ13C of needles from red pine (Pinus densiflora f. aggregate Nakai) saplings grown for 25 weeks in artificially acidified soils (pH 3.5) with and without FA. Sapling growth increments were measured, and both soil and needle samples were collected. Soil samples were assessed for pH, exchangeable cations, and mineral N concentrations. Needle samples were analyzed for δ13C, N concentration, δ15N, and cations concentrations. FA application significantly enhanced (P < 0.001) tree growth by increasing soil pH (by > 4.0 units) and Ca2+ concentration (by over two-fold). FA also reduced soil NH4+ levels (P < 0.001), accompanied by a corresponding increase in NO3− concentration, which indirectly indicates enhanced nitrification. The increase in needle δ15N values (P < 0.05), from 4.3–4.6‰ without FA to 5.4–5.7‰ with FA, further indirectly supported increased N availability and losses associated with nitrification. In contrast, needle δ13C values were unaffected by FA treatment, suggesting that stomatal conductance and carboxylation rate increased proportionally. Our findings demonstrate that FA can serve as a soil amendment for remediating acidic forest soils to improve tree growth by enhancing N cycling and alleviating soil acidity.