Soils contain the largest amount of land carbon, even a small change of this pool can significantly affect atmospheric CO₂ and climate change. A good representation of soil organic carbon (SOC) dynamics in Earth system models is therefore crucial to predict future climate change. The dynamics of SOC is largely driven by microbial activities and modulated by N cycles. Nevertheless, very few models have explicitly represented soil microorganisms and N cycles integrated at global scale. Here, we present an update of the microbial-mediated ORCHIMIC model and its application to simulate global gridded SOC stocks, microbial biomass, soil C/N ratio, microbial C/N ratio, and heterotrophic respiration. This is a new attempt to model SOC dynamics with an explicit microbial representation with N dynamics applied at global scale. The model shows relatively good performance in reproducing global SOC and microbial biomass C. The spatial distributions of soil and microbial C/N ratios were not well reproduced because they are sensitive to mineral nitrogen availability controlled by plant uptake, which is not explicitly represented in the model. However, similar relationship between C/N ratios of microbes and soil as observation demonstrated the potential of the model to reproduce global C/N ratios for both microbe and soil pools. Dynamic carbon use efficiency modulated by substrate C/N ratio, consistent with observation, were well represented by mechanistic including microbial dynamics. Modeled suppressed microbial biomass growth under warming climate indicating a weaker positive feedback between soil C pool and climate compared to that predicted by traditional Earth system models.

中文翻译：

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使用微生物分解模型 ORCHIMIC v2.0 对土壤有机质和微生物碳氮储量进行全局模拟和评价

土壤中的陆地碳含量最高，即使这个池的微小变化也会对大气 CO ₂产生显着影响和气候变化。因此，地球系统模型中土壤有机碳 (SOC) 动态的良好表现对于预测未来的气候变化至关重要。SOC的动力学主要由微生物活动驱动，并由N个周期调节。然而，很少有模型明确地代表了在全球范围内整合的土壤微生物和氮循环。在这里，我们介绍了微生物介导的 ORCHIMIC 模型的更新及其在模拟全球网格 SOC 储量、微生物生物量、土壤 C/N 比、微生物 C/N 比和异养呼吸方面的应用。这是使用在全球范围内应用 N 动态的显式微生物表示来模拟 SOC 动态的新尝试。该模型在再生全球 SOC 和微生物生物量 C 方面表现出较好的性能。土壤和微生物 C/N 比的空间分布没有很好地再现，因为它们对植物吸收控制的矿物氮可用性敏感，这在模型中没有明确表示。然而，微生物和土壤 C/N 比之间的类似关系作为观察证明了该模型具有重现微生物和土壤池的全球 C/N 比的潜力。由底物碳氮比调节的动态碳利用效率与观察结果一致，可以通过包括微生物动力学在内的机制很好地表示出来。模拟在变暖气候下抑制微生物生物量的增长，表明与传统地球系统模型预测的相比，土壤碳库和气候之间的正反馈较弱。