## 4 Discussion  
Extreme drought events can affect the structure and function of an ecosystem and result in a longer restoration process for the ecosystem or in a continuous change of the system state [8; 11; 33]. The carbon cycle is an important ecological process occurring within each ecosystem. Carbon sequestration and carbon emission are two essential parts of the carbon cycle and are closely related to water availability [44]. By controlling precipitation to simulate extreme drought, it was found that extreme drought events significantly reduced the GPP, \(\mathrm{R_{e}}\), and \(\mathrm{CH_{4}}\) fluxes of the peatland ecosystem in the Zoige plateau, and the effect of extreme drought on GPP was clearly greater than the effect on \(\mathrm{R_{e}}\). Thus, the carbon sink function of this ecosystem was significantly reduced, which was the same conclusion as that previously reported by [PERSON] et al., and the GPP was more sensitive to extreme drought events than \(\mathrm{R_{e}}\)[45]. According to the prior study by [PERSON] et al., extreme drought was defined as 30 days' rain-free period based on the local weather data for the most recent 58 years, and they found that extreme drought decreased GPP and to a lesser extent \(\mathrm{R_{e}}\), leading to reduced net ecosystem \(\mathrm{CO_{2}}\) uptake [45], which were consistent with our results. Precipitation is the critical factor affecting the sensitivity of GPP to extreme drought and the degree to which photosynthesis decreases during  
Figure 8: Interactive effects of soil temperature and soil water content on NEE, GPP, \(\mathrm{R_{e}}\) and \(\mathrm{CH_{4}}\). The heat map is based on the partial residuals of the smooth terms (soil temperature and soil water content) used in generalized additive models. Because of negative values of NEE, the yellow and blue color represents low and high carbon sink, respectively (**a**). Light and dark blue represents \(\mathrm{CH_{4}}\) uptake and emission, respectively (**d**). a drought depends on the physiological response of the plants to the available water and the changes occurring in the vegetation structure [46]. The physiological response of vegetation to drought includes a decrease in enzyme activity and the closing of stomata to prevent water loss [47]. Under extreme drought conditions, water stress can reduce the stomatal conductance of plant leaves, which leads to decreased photosynthetic and transpiration rates [48]. Additionally, the number and activity of microbes decrease sharply under extreme drought conditions [22], and this is likely the main reason for the decrease in NEE, \(\mathrm{R_{e}}\), and GPP within an ecosystem. Additionally, extreme drought can create a carry-over effect on the carbon flux of an ecosystem in the later stages. Short-term drought effects can potentially alter plant growth dynamics and ecosystem physiology, and the impact on ecosystems may not be immediately apparent; however, a \"memory\" function in relation to drought by an ecosystem can promote a \"carry-over-effect\" from one growing season to the next [49; 50]. Soil water content is an indicator of soil's ability to supply water to plant root systems and soil microorganisms. When the soil water content is too low, plant physiological activity is blocked, which results in the decrease of the plant photosynthetic capacity and respiratory intensity [47]. This study showed that there was a significant correlation between soil water content and the ecosystem NEE, \(\mathrm{R_{e}}\), and GPP at 5 cm, 10 cm, and 20 cm of soil depth. Recent studies have also shown that increasing precipitation increases carbon storage in peatlands, while the decrease in soil moisture will reduce carbon storage [51]. Extreme drought can significantly change the soil moisture state of an ecosystem, causing a significant decrease in soil water content, photosynthesis of aboveground plants, and enzyme activity during respiration as well as inhibit enzyme reactions performed by underground microorganisms [48].