Due to their substantial volume, subsoils contain more of the total soil carbon (C) pool than topsoils. Much of this C is thousands of years old, suggesting that subsoils offer considerable potential for long-term C sequestration. However, knowledge of subsoil C behaviour and manageability remains incomplete, and subsoil C storage potential has yet to be realised at a large scale, particularly in agricultural systems. A range of biological (e.g. deep-rooting), chemical (e.g. biochar burial) and physical (e.g. deep ploughing) C sequestration strategies have been proposed, but are yet to be assessed. In this review, we identify the main factors that regulate subsoil C cycling and critically evaluate the evidence and mechanistic basis of subsoil strategies designed to promote greater C storage, with particular emphasis on agroecosystems. We assess the barriers and opportunities for the implementation of strategies to enhance subsoil C sequestration and identify 5 key current gaps in scientific understanding. We conclude that subsoils, while highly heterogeneous, are in many cases more suited to long-term C sequestration than topsoils. The proposed strategies may also bring other tangible benefits to cropping systems (e.g. enhanced water holding capacity and nutrient use efficiency). Furthermore, while the subsoil C sequestration strategies we reviewed have large potential, more long-term studies are needed across a diverse range of soils and climates, in conjunction with chronosequence and space-for-time substitutions. Also, it is vital that subsoils are more consistently included in modelled estimations of soil C stocks and C sequestration potential, and that subsoil-explicit C models are developed to specifically reflect subsoil processes. Finally, further mapping of subsoil C is needed in specific regions (e.g. in the Middle East, Eastern Europe, South and Central America, South Asia and Africa). Conducting both immediate and long-term subsoil C studies will fill the knowledge gaps to devise appropriate soil C sequestration strategies and policies to help in the global fight against climate change and decline in soil quality. In conclusion, our evidence-based analysis reveals that subsoils offer an untapped potential to enhance global C storage in terrestrial ecosystems.

由于它们的体积很大，底土比表土含有更多的土壤总碳 (C) 库。其中大部分 C 已有数千年的历史，这表明底土为长期 C 封存提供了相当大的潜力。然而，关于地下碳行为和可管理性的知识仍然不完整，地下碳储存潜力尚未大规模实现，特别是在农业系统中。已经提出了一系列生物（例如深根）、化学（例如生物炭掩埋）和物理（例如深耕）固碳策略，但尚待评估。在这篇综述中，我们确定了调节地下碳循环的主要因素，并批判性地评估了旨在促进更大碳储存的地下战略的证据和机制基础，特别强调了农业生态系统。我们评估了实施加强底土固碳战略的障碍和机遇，并确定了当前科学认识方面的 5 个关键差距。我们得出结论，底土虽然高度异质，但在许多情况下比表土更适合长期固碳。提议的战略还可能为种植系统带来其他切实的好处（例如提高持水能力和养分利用效率）。此外，虽然我们审查的地下土壤碳封存策略具有巨大潜力，但需要在不同的土壤和气候范围内进行更长期的研究，并结合时间序列和时空替代。此外，将底土更一致地纳入土壤碳库和碳封存潜力的模型估计中也很重要，并且开发了底土显式 C 模型以专门反映底土过程。最后，需要在特定地区（如中东、东欧、南美洲和中美洲、南亚和非洲）进一步绘制底土 C 绘图。开展即时和长期地下碳研究将填补知识空白，以制定适当的土壤碳封存战略和政策，以帮助全球应对气候变化和土壤质量下降。总之，我们的循证分析表明，底土具有未开发的潜力，可以增强陆地生态系统中的全球碳储存。开展即时和长期地下碳研究将填补知识空白，以制定适当的土壤碳封存战略和政策，以帮助全球应对气候变化和土壤质量下降。总之，我们的循证分析表明，底土具有未开发的潜力，可以增强陆地生态系统中的全球碳储存。开展即时和长期地下碳研究将填补知识空白，以制定适当的土壤碳封存战略和政策，以帮助全球应对气候变化和土壤质量下降。总之，我们的循证分析表明，底土具有未开发的潜力，可以增强陆地生态系统中的全球碳储存。