## 1 Introduction  
The latest assessment report released by the United Nations Intergovernmental Panel on Climate Change (IPCC) shows that the intensification of human activity has dramatically changed the global pattern of the atmospheric cycle. Extreme weather events, especially extreme drought events,have shown an increasing trend over the past 50 years and will likely become more frequent in the future [1; 2; 3; 4; 5]. Extreme drought events change key processes in the water cycle, and subsequently affect the carbon and nitrogen cycling processes of an ecosystem, thus breaking the original carbon sink pattern and causing changes in the structure and function of terrestrial ecosystems [6; 7; 8]. In turn, this significantly affects the trends and intensity of global climate change [9]. Extreme drought events have become the main ecological factors affecting the security of global ecosystems due to their high intensity, wide range, and low predictability [10; 11; 12]. Therefore, it is critical to quantitatively study and predict the impact of extreme drought events on the carbon budget of an ecosystem. However, previous studies have mostly focused on the response of carbon source/sink functions in ecosystems relative to long-term trends in climate change and have neglected the impact of short-term extreme drought events and their mechanisms [2; 13], restricting the ability to understand and predict the ecological consequences of climate change and to adopt adaptive countermeasures. The peatland ecosystem is an essential component of the global terrestrial carbon pool. This ecosystem stores 15-30% of the global soil carbon pool at a proportion of only 3% of the total land area, which plays a vital role in regulating global climate change [14; 15; 16; 17]. The carbon budget in the peatland ecosystem is greatly affected by meteorological factors (temperature, precipitation, light, etc. ), plant physiological changes, and soil microbial changes [18; 19; 20]. Moreover, extreme drought events can significantly affect the temperature and hydrological conditions of a given ecosystem [21], and can change the water balance, aggravate the degree of water stress, significantly affect plant growth [22; 23; 24] and respiration [25], and alter decomposition of organic matter [26] as well as change carbon, water, and energy fluxes between the land surface and the atmosphere [27]. Additionally, extreme drought events can reduce the availability of substrates for microbial respiration [28], have effects on plant physiological states and soil microbial activity, and have an impact on the carbon budget dynamics in peatland ecosystems, which makes the conversion of carbon source/sink function very uncertain [29; 30]. As such, exploring the impacts of extreme drought on carbon budgets of the peatland ecosystem is of great practical significance. Such studies will further the understanding of fluctuating carbon budgets on both the regional and global scale, help protect wetland ecological resources, and provide data to support measures that slow down greenhouse effects [10]. Located in the northeast corner of the Qinghai-Tibet Plateau, the peatland of the Zoige plateau is the highest and largest peat swamp area in the world. The thickness of the peat is 0.3-3.8 m, with a dry weight of 2.9 Pg [31]. As such, it is typical and representative in the study of the global carbon cycle as it relates to the peatland ecosystem. Additionally, the peatland of the Zoige plateau is also one of the most sensitive areas in regard to global climate change, and is extremely vulnerable to the effects of long-term climate changes [32; 33; 34; 35]. Long-term climate change is characterized at this site by a warming and drying trend and an increasing frequency of extreme drought events [16; 19].