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<p>Metal salts-modified sewage sludge (SS) biochar is increasingly used in agricultural soil remediation, although its effects on available phosphorus (P) species, plant growth and microbial communities remain unclear. This study prepared CaO, CaCl<sub>2</sub>, MgO and MgCl<sub>2</sub>-modified hydrochars derived from SS at 260 °C for 2&#xa0;h. Then the available P characteristics of the hydrochars and their effects on the growth of <i>Vigna radiata</i> (mung bean) and soil microorganisms were comprehensively evaluated by chemical extraction, pot experiments and the diffusive gradients in thin-films (DGT) technique. Results indicated that Ca-based hydrochars contained more slow-release apatite P (AP) compounds (e.g., Ca<sub>5</sub>(PO<sub>4</sub>)<sub>3</sub>OH, Ca<sub>5</sub>(PO<sub>4</sub>)<sub>3</sub>Cl and Ca<sub>2</sub>PO<sub>4</sub>Cl), with a 48.6%–86.3% increase in AP content compared to the control at 260&#xa0;°C. In contrast, Mg-based hydrochars were richer in easy-release AP compounds (e.g., Mg<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> and Ca<sub>3</sub>Mg<sub>3</sub>(PO<sub>4</sub>)<sub>4</sub>), with a lower AP increase of 0–50.7%. Compared with Ca salts modified hydrochars, Mg-modified hydrochars (especially MgO) were more effective for the promotion of rapid growth, chlorophyll synthesis and photosynthesis in <i>V. radiata</i> plants, resulting in more P accumulation within mung beans, which was consistent with the P release results obtained by DGT. The addition of Ca-modified hydrochars promoted the enrichment of bacterial communities such as <i>Skermanella</i> and <i>RB41</i>, which was helpful for improving the mineralization and circulation of P in soil. While the addition of Mg-modified hydrochars to soils enhanced the activity of P-solubilizing bacteria such as <i>Pseudomonas</i> and <i>Bacillus</i>, which was conducive to the dissolution and utilization of P. This highlights Ca-based hydrochars as a stable long-term P source and Mg-based hydrochars for rapid plant uptake, offering a novel strategy for P fertilizer application.</p> Graphical Abstract <p></p>

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Soil–plant-microbial evidence for the available phosphorus generation and utilization of Ca/Mg salts conditioned hydrochar from sewage sludge

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年9月17日

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  • Qian Zhao,
  • Wei Guo,
  • Yuhan Zhu,
  • Dongyue Li,
  • Xiaohui Liu,
  • Minda Yu,
  • Dongyang Li,
  • Xiang Gao,
  • Xishi Tai,
  • Jun Li

摘要

Metal salts-modified sewage sludge (SS) biochar is increasingly used in agricultural soil remediation, although its effects on available phosphorus (P) species, plant growth and microbial communities remain unclear. This study prepared CaO, CaCl2, MgO and MgCl2-modified hydrochars derived from SS at 260 °C for 2 h. Then the available P characteristics of the hydrochars and their effects on the growth of Vigna radiata (mung bean) and soil microorganisms were comprehensively evaluated by chemical extraction, pot experiments and the diffusive gradients in thin-films (DGT) technique. Results indicated that Ca-based hydrochars contained more slow-release apatite P (AP) compounds (e.g., Ca5(PO4)3OH, Ca5(PO4)3Cl and Ca2PO4Cl), with a 48.6%–86.3% increase in AP content compared to the control at 260 °C. In contrast, Mg-based hydrochars were richer in easy-release AP compounds (e.g., Mg3(PO4)2 and Ca3Mg3(PO4)4), with a lower AP increase of 0–50.7%. Compared with Ca salts modified hydrochars, Mg-modified hydrochars (especially MgO) were more effective for the promotion of rapid growth, chlorophyll synthesis and photosynthesis in V. radiata plants, resulting in more P accumulation within mung beans, which was consistent with the P release results obtained by DGT. The addition of Ca-modified hydrochars promoted the enrichment of bacterial communities such as Skermanella and RB41, which was helpful for improving the mineralization and circulation of P in soil. While the addition of Mg-modified hydrochars to soils enhanced the activity of P-solubilizing bacteria such as Pseudomonas and Bacillus, which was conducive to the dissolution and utilization of P. This highlights Ca-based hydrochars as a stable long-term P source and Mg-based hydrochars for rapid plant uptake, offering a novel strategy for P fertilizer application.

Graphical Abstract