Abstract. Large herbivore grazing has been shown to substantially alter tundra soil and vegetation properties as well as carbon fluxes, yet observational evidence to quantify the impact of herbivore introduction into Arctic permafrost ecosystems remains sparse. In this study we investigated growing season CO₂ and CH₄ fluxes with flux chambers on a former wet tussock tundra inside Pleistocene Park, a landscape experiment in Northeast Siberia with a 22 year history of grazing. Reference data for an undisturbed system were collected on a nearby ungrazed tussock tundra. Linked to a reduction in soil moisture, topsoil temperatures at the grazed site reacted one order of magnitude faster to changes in air temperatures compared to the ungrazed site and were significantly higher, while the difference strongly decreased with depth. Overall, both GPP (gross primary productivity, i.e. CO₂ uptake by photosynthesis) and R_eco (ecosystem respiration, i.e. CO₂ release from the ecosystem) were significantly higher at the grazed site with notable variations across plots at each site. The increases in CO₂ component fluxes largely compensated each other, leaving NEE (net ecosystem exchange) similar across grazed and ungrazed sites for the observation period. Soil moisture and CH₄ fluxes at the grazed site decreased over the observation period, while in contrast the constantly water-logged soils at the ungrazed site kept CH₄ fluxes at significantly higher levels. Our results indicate that grazing of large herbivores promotes topsoil warming and drying, effectively accelerating CO₂ turnover while decreasing methane emissions. Our experiment did not include autumn and winter fluxes, and thus no inferences can be made for the annual NEE and CH₄ budgets at tundra ecosystems.

中文翻译：

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放牧增强了碳循环，但减少了西伯利亚更新世公园苔原遗址的甲烷排放

摘要。大型食草动物放牧已被证明会显着改变苔原土壤和植被特性以及碳通量，但量化食草动物引入北极永久冻土生态系统影响的观察证据仍然很少。在这项研究中，我们调查了生长季节CO ₂和CH ₄更新世公园内前湿草丛苔原上的通量室与通量室，这是在西伯利亚东北部进行的景观实验，具有 22 年的放牧历史。未受干扰系统的参考数据是在附近未放牧的草丛苔原上收集的。与土壤水分减少有关，放牧地表土温度对气温变化的反应比未放牧地快一个数量级，而且明显更高，而差异随着深度的增加而显着降低。总体而言，GPP（总初级生产力，即光合作用对CO _{2 的}吸收）和R _eco（生态系统呼吸，即CO ₂从生态系统中释放）在放牧地点显着更高，每个地点的地块之间都有显着差异。CO ₂组分通量的增加在很大程度上相互补偿，使观察期内放牧和未放牧地点的NEE（净生态系统交换）相似。放牧地点的土壤水分和CH ₄通量在观察期内下降，而相比之下，未放牧地点的持续浸水土壤使CH ₄通量保持在显着较高的水平。我们的结果表明，大型食草动物的放牧促进了表层土壤的变暖和干燥，有效地加速了CO ₂营业额，同时减少甲烷排放。我们的实验不包括秋季和冬季通量，因此无法推断苔原生态系统的年度NEE和CH ₄预算。