Abstract During the early to middle Holocene, the Sahara received enhanced precipitation and was covered by steppe-like vegetation with a large-scale hydrographic network of lakes, wetlands and fans, which is known as the Green Sahara (GS). However, most coupled land-atmosphere models underestimate the precipitation and vegetation cover, suggesting that critical atmospheric or land surface processes are lacking in those models. Climate-induced vegetation cover change can modify soil texture and physical properties over the long term, which in turn have feedbacks on vegetation. In this study, we examine five plausible soil-vegetation processes in a land surface model, which are expected to increase soil moisture for plants and possibly sustain equilibrium vegetation for a lower rainfall level. The annual precipitation required during the GS epoch to match the modelled vegetation distribution with paleorecords is inferred. Results demonstrate that these soil-vegetation processes have strong positive impacts on vegetation and soil moisture, especially the increase of soil evaporative resistance. After including all soil feedbacks on vegetation, the model requires only a mean precipitation of ∼400 mm/yr to reproduce the pollen-inferred GS vegetation, instead of ∼600 mm/yr when no soil feedback is included. From the mid-Holocene to pre-industrial period, we infer that terrestrial carbon stocks decrease by ∼58 PgC due to the removal of carbon in vegetation, soil and litter pools of the GS. This work highlights the importance of soil-vegetation interactions for simulating dry-region vegetation coverage in models, and the impacts of natural land cover change on carbon budgets in the geological past.

中文翻译：

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绿色撒哈拉时期土壤性质对植被的反馈

摘要 早、中全新世，撒哈拉地区降水增强，被草原状植被覆盖，形成了大规模的湖泊、湿地和扇形水文网络，被称为绿色撒哈拉（GS）。然而，大多数耦合陆地-大气模型低估了降水和植被覆盖，这表明这些模型中缺乏关键的大气或地表过程。气候引起的植被覆盖变化可以长期改变土壤质地和物理特性，进而对植被产生反馈。在这项研究中，我们检查了地表模型中五种可能的土壤植被过程，这些过程预计会增加植物的土壤水分，并可能在较低的降雨水平下维持植被的平衡。推断出 GS 时期与模拟植被分布与古记录相匹配所需的年降水量。结果表明，这些土壤-植被过程对植被和土壤水分有很强的积极影响，特别是土壤蒸发阻力的增加。在包括对植被的所有土壤反馈后，该模型只需要~400 毫米/年的平均降水量来重现花粉推断的 GS 植被，而不是在不包括土壤反馈时~600 毫米/年。从全新世中期到工业化前时期，我们推断由于 GS 植被、土壤和枯枝落叶池中碳的去除，陆地碳储量减少了约 58 PgC。这项工作强调了土壤-植被相互作用对于模拟模型中干旱地区植被覆盖的重要性，