Background and aims

Afforestation or reforestation with mixed tree species is a promising strategy for carbon sequestration and climate change mitigation. However, whether soil organic carbon (SOC) stability in mixed-species forests (MF) is higher than that of monoculture forests (PF) is unclear.

Methods

The origin and stability of SOC were investigated using soil samples (1 m in depth) obtained from 12 pairs of monoculture and polyculture plots, which included four age classes.

Results

We found that the contents of SOC and its components were higher in mixed-species forests than in monoculture forests, particularly in the 0–40 cm soil layer and middle-aged (33–45 years) PF. In middle-aged forests, the MF had a smaller percentage of microbial-derived C and mineral-associated organic carbon (MAOC) to total SOC ratio than those of PF. However, the ratio of MAOC to total SOC in the MF was considerably higher than that in old-aged PF (62 years), indicating that transforming old-aged PF into MF aids SOC stabilization. Mineral protection played a major role in influencing the accumulation of plant-derived C, microbial-derived C, and SOC fractions in the PF, whereas total nitrogen and ammonium nitrogen played a dominant role in the MF.

Conclusion

This study provides new evidence that transforming single-species monocultures into mixed-species polycultures is beneficial for the accumulation and stabilization of SOC in subtropical forests and highlights that these effects depend on the influence of forest age and soil depth on organic carbon fractions.

中文翻译：

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树种混混促进中龄表层土壤有机碳积累和老龄林稳定性

 背景和目标

混树种植树造林或重新造林是碳封存和减缓气候变化的一种很有前途的策略。然而，混交林 （MF） 的土壤有机碳 （SOC） 稳定性是否高于单一物种林 （PF） 尚不清楚。

 方法

使用从 12 对单一和混作样地（包括 4 个年龄组）获得的土壤样品 （1 m 深） 研究了 SOC 的来源和稳定性。

 结果

我们发现，混交林中 SOC 及其成分的含量高于单一栽培林，尤其是在 0-40 cm 土层和中龄 （33-45 年） PF 中。在中龄林中，MF 的微生物衍生 C 和矿物相关有机碳 （MAOC） 与总 SOC 的比率低于 PF。然而，MF 中 MAOC 与总 SOC 的比率远高于老年 PF （62 岁），表明将老年 PF 转化为 MF 有助于 SOC 稳定。矿物质保护在影响 PF 中植物来源的 C、微生物来源的 C 和 SOC 组分的积累中起主要作用，而总氮和铵态氮在 MF 中起主导作用。

 结论

本研究提供了新的证据，表明将单一物种单一栽培转化为混合物种混养有利于亚热带森林 SOC 的积累和稳定，并强调这些影响取决于森林年龄和土壤深度对有机碳组分的影响。