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Background and aims <p>Monoculture plantations cover 56.5% of the total plantation area on Loess Plateau, China. Their uniform stand structure leads to lower soil carbon sequestration efficiency compared to mixed plantations. However, the mechanisms by which mixed plantations influence stand architecture, soil organic carbon (SOC) and its stability across different vegetation zones remain unclear. Moreover, how the quantity and quality of SOC sources affecting SOC and carbon fractions are poorly understood. These gaps lead to underestimating the contributions of mixed plantations for better carbon sequestration.</p> Methods <p>This study focused on <i>Robinia pseudoacacia</i> monocultures and mixed plantations (<i>R. pseudoacacia</i> with <i>Pinus tabuliformis</i>, <i>Prunus sibirica</i>, or <i>Platycladus orientalis</i>) in forest and forest-steppe zones on the Loess Plateau. We examined the relationships among stand structure, understory vegetation diversity, litter composition, SOC content, and its stabilization (particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) fractions).</p> Results <p><i>R. pseudoacacia</i> mixed with <i>P. tabuliformis</i> or <i>P. orientalis</i> significantly increased SOC content in both zones, suggesting that conifer-broadleaf mixed plantations have the potential to enhance SOC stocks. Redundancy analysis showed that tree leaf biomass was positively correlated with SOC (50.1% variance explained), whereas tree leaf C/N ratio was negatively correlated with SOC (29.5% variance explained), indicating their coupled regulation on SOC dynamics. Mixed plantations enhanced understory herb layer diversity in both forest and forest-steppe zones. In forest zones, herb layer diversity was positively correlated with SOC, POC, and MAOC, indicating that herb layer diversity drives SOC accumulation and stabilization.</p> Conclusions <p>This study reveals the role of mixed plantations in regulating SOC in both zones, thereby providing clear evidence of carbon-efficient afforestation on the Loess Plateau.</p> Graphical abstract <p></p>

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Conifer-broadleaf mixed plantations enhance soil organic carbon in vegetation zones of Loess Plateau

  • 期刊论文

  • 发表日期：

    2026年2月3日

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  • Ke Zhang,
  • Qi Liu,
  • Xianglin Chen,
  • Shiqi Zhang,
  • Guobin Liu,
  • Guoliang Wang,
  • Ying Liu

摘要

Background and aims

Monoculture plantations cover 56.5% of the total plantation area on Loess Plateau, China. Their uniform stand structure leads to lower soil carbon sequestration efficiency compared to mixed plantations. However, the mechanisms by which mixed plantations influence stand architecture, soil organic carbon (SOC) and its stability across different vegetation zones remain unclear. Moreover, how the quantity and quality of SOC sources affecting SOC and carbon fractions are poorly understood. These gaps lead to underestimating the contributions of mixed plantations for better carbon sequestration.

Methods

This study focused on Robinia pseudoacacia monocultures and mixed plantations (R. pseudoacacia with Pinus tabuliformis, Prunus sibirica, or Platycladus orientalis) in forest and forest-steppe zones on the Loess Plateau. We examined the relationships among stand structure, understory vegetation diversity, litter composition, SOC content, and its stabilization (particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) fractions).

Results

R. pseudoacacia mixed with P. tabuliformis or P. orientalis significantly increased SOC content in both zones, suggesting that conifer-broadleaf mixed plantations have the potential to enhance SOC stocks. Redundancy analysis showed that tree leaf biomass was positively correlated with SOC (50.1% variance explained), whereas tree leaf C/N ratio was negatively correlated with SOC (29.5% variance explained), indicating their coupled regulation on SOC dynamics. Mixed plantations enhanced understory herb layer diversity in both forest and forest-steppe zones. In forest zones, herb layer diversity was positively correlated with SOC, POC, and MAOC, indicating that herb layer diversity drives SOC accumulation and stabilization.

Conclusions

This study reveals the role of mixed plantations in regulating SOC in both zones, thereby providing clear evidence of carbon-efficient afforestation on the Loess Plateau.

Graphical abstract