1. Due to complex root–soil interactions, the responses of carbon (C) dynamics in the rhizosphere to elevated nitrogen (N) deposition may be different from those in bulk soil. However, the potentially different response of C dynamics in the rhizosphere and bulk soils and their contributions to soil C sequestration under N deposition is still not elucidated.
2. We conducted an N addition experiment in an alpine shrubland dominated by Sibiraea angustata located on the eastern Qinghai‐Tibet Plateau (QTP). We measured the soil organic C (SOC) contents and density fractions in the rhizosphere and bulk soils in the top 15 cm of mineral soil and then employed a numerical model based on the rhizosphere extent to evaluate how the rhizosphere modulates soil C sequestration under N addition. We also measured the microbial gene abundance and C‐acquisition enzyme activities to assess microbial community responses to N addition.
3. The results showed that nitrogen addition had opposite effects on the rhizosphere and bulk‐soil C stocks. Specifically, N addition decreased the rhizosphere SOC content by increasing bacterial abundance, β‐glucosidase activity, and thus accelerating the loss of free light fraction C (FLF‐C). However, N addition increased the bulk‐soil C content, which was corresponding with the reduced oxidase activities and the accelerated accumulation of heavy fraction C (HF‐C) under N addition. Numerical model analysis showed that the decrease induced by N addition in rhizosphere SOC stock ranged from 0.11 to 3.01 kg C/m² as root exudation diffusion distance extended from 0.5 to 2 mm, while the corresponding increase in the bulk‐soil C stock ranged from 1.91 to 4.08 kg C/m². By synthesizing the dynamics of the SOC stocks in these two soil compartments under N addition, the SOC stock at the ecosystem level exhibited an increase in range of 0.73–2.44 kg C/m².
4. Synthesis. Our results suggest that alpine shrublands on the eastern QTP have great potential for soil C sequestration under N deposition, and the magnitude of the sequestration would depend closely on the responses of rhizosphere microbial C processes and the rhizosphere extent. Our results highlight the importance of integrating rhizosphere processes into land surface models to accurately predict ecosystem functions in the background of elevated N deposition.

中文翻译：

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高寒灌丛中氮素添加对根际和土壤固碳的不同影响

1. 由于复杂的根-土相互作用，根际中碳（C）动态对升高的氮（N）沉积的响应可能不同于散装土壤中的响应。然而，仍未阐明根际土壤和块状土壤中碳动力学的潜在不同响应及其在氮沉降下对土壤碳固存的贡献。
2. 我们在位于青藏高原东部（QTP）的以西伯利亚虎耳草为主的高山灌丛中进行了氮素添加实验。我们测量了15 cm矿物土壤中根际和块状土壤中土壤有机碳（SOC）的含量和密度分数，然后基于根际范围使用数值模型来评估在添加氮的情况下根际如何调节土壤固碳。我们还测量了微生物基因的丰度和C-收购酶的活性，以评估微生物群落对氮添加的反应。
3. 结果表明，氮的添加对根际和大宗土壤C储量有相反的影响。具体而言，氮的添加通过增加细菌的丰度和β-葡萄糖苷酶的活性而降低了根际SOC含量，从而加速了游离光分数C（FLF-C）的损失。但是，氮的添加增加了大块土壤C的含量，这与减少的氧化酶活性和氮的添加下重组分C（HF-C）的加速积累相对应。数值模型分析表明，随着根系渗出扩散距离从0.5mm增加到2mm，根际SOC储量中氮的添加量范围从0.11至3.01 kg C / m ²，而土壤块状C储量的相应增加量为0.11至3.01 kg C / m ²。 1.91至4.08 kg C / m ²。通过在氮添加的基础上综合这两个土壤隔室中SOC储量的动态，生态系统水平上的SOC储量范围增加了0.73–2.44 kg C / m ²。
4. 综合。我们的研究结果表明，东部QTP上的高寒灌丛在氮沉降下具有固碳的巨大潜力，固碳的程度将紧密依赖于根际微生物C的反应和根际范围。我们的结果突出了将根际过程整合到土地表面模型中以准确预测氮沉降增加背景下的生态系统功能的重要性。