土壤水分是影响土壤中碳迁移的重要因素。水分入渗作为土壤中物质传输的关键途径，改变了土壤水分的垂直分布特征，同时驱动着土壤溶解碳的垂直迁移。高寒草甸生态系统具有重要的生态服务功能，但由于当前对土壤垂直剖面高频连续碳水观测数据的缺乏，其土壤水分及溶解碳垂直运移过程尚不清楚。因此，本研究以青海湖流域高寒草甸生态系统为研究对象，结合蒸渗仪土壤碳水高频观测系统及稳定同位素方法，量化了高寒草甸生态系统生长季降水和不同深度土壤水分及其氢氧稳定同位素的季节变化特征，辨明了不同场次降水在土壤垂直剖面的下渗阈值，厘清了场次降水入渗过程及其对不同深度土壤水分的贡献和时滞效应，明确了水分入渗对不同深度土壤溶解碳的影响，揭示了高寒区土壤水分和溶解碳垂直运移过程及其对场次降水的响应。研究结果加深了对高寒草甸生态系统碳水垂直运移过程的理解，对认识气候变化背景下青藏高原水资源利用与碳中和战略具有重要科学意义。论文主要结论如下：
（1）青海湖千户里小流域2022年和2023年生长季（6~10月）平均降水量为377.4 mm，平均土壤体积含水量为15.74%，并随气温变化和土层深度增加先增后减。2022年和2023年间，共发生195场降水，降水量级为0~5 mm、5~10 mm、10~15 mm和15 mm以上的降水分别占总降水量的24.51%、18.89%、14.41%和42.19%。垂直剖面上10 cm、30 cm和75 cm土壤平均体积含水量分别为10.24%、30.64%和6.34%，土壤含水量随着土壤深度先升高后降低，30 cm深度土壤含水量最高。随着生长季温度的升高，土壤含水量不断增加，与降水变化表现出相对同步的趋势。2022年和2023年降水氢氧稳定同位素平均值分别是-35.41‰和-6.69‰，土壤氢氧稳定同位素平均值分别是-41.16‰和-6.75‰，分布相对聚集，水分补给以降水为主，同时受到蒸发和其他水源的混合影响。
（2）高寒草甸生态系统10 cm、30 cm和75 cm深度土壤水分对降水的响应阈值分别为3 mm、15 mm和17 mm，响应滞后时间受制于土壤深度和降水条件，在1~3天不等，不同深度土壤水分来源受降水条件的影响差异明显。10 cm深度土壤水分在降水量小于20 mm时对降水的响应存在约2天的滞后，而大于20 mm量级的降水会在发生后1~9天持续影响土壤水分，且降水对该层水分的贡献率为10%~32%。30 cm深度土壤水分受降水量、前期含水量及上层土壤含水量的共同影响，在降水量大于15 mm时平均的响应滞后时间约为3天；在大于20 mm的降水发生后3~11天持续响应。当连续降水发生时，10 cm深度土壤水分对当日场次降水响应最剧烈，可受到11.5%~46%的降水补给，而30 cm深度土壤水分受到前期降水的补给比例更高，在11%~27%之间。
（3）高寒草甸生态系统不同深度土壤中溶解有机碳（DOC）和溶解无机碳（DIC）时空分布规律明显不同，0~20 cm、20~50 cm和50~80 cm土壤层平均接收的DOC和DIC入渗量分别能够达到自身含量的227.56%和146.63%，-3.36%和24.32%及22.11%和22.02%，DOC和DIC入渗量对不同降水条件的响应特征存在差异。生长季土壤平均DOC浓度为29.21 mg/L，在6~9月呈现先升高后降低的趋势；土壤垂直剖面上，DOC浓度呈现随土壤深度增加而降低的趋势。生长季土壤平均DIC浓度为23.43 mg/L，在6~9月不断升高；垂直剖面上DIC含量从浅层到深层不断升高。随着降水量的增加及水分的入渗，0~20 cm土壤中DOC入渗量与滞后2场次的降水量显著正相关（R² = 0.36）；而DIC入渗量受降水DIC的影响显著（R² = 0.52）。降水量越大，20~50 cm土壤溶解碳输入越多，输出的DOC增多而DIC减少。50~80 cm土壤DOC和DIC输入主要受降水量影响。DOC表现为由浅层向深层迁移，DIC除受自上而下随水分迁移影响，土壤还能接收溶解碳酸盐中的DIC。

Soil water is an important factor affecting carbon transport in soil. Water infiltration, as a key way of material transport in soil, changes the vertical distribution characteristics of soil water and drives the vertical migration of dissolved carbon in soil. Alpine meadow ecosystem has important ecological service function, but due to the lack of high-frequency continuous carbon and water observation data of soil vertical profile, the vertical transport process of soil water and dissolved carbon is still unclear. Therefore, this study took the alpine meadow ecosystem of Qinghai Lake Basin as the research object, combined with the high frequency observation system of soil carbon and water by lysimeter and the stable isotope method, quantified the seasonal variation characteristics of the growing season precipitation, soil moisture at different depths and its stable hydrogen and oxygen isotopes of the alpine meadow ecosystem, and identified the infiltration threshold of different rainfall in the soil vertical profile. The process of precipitation infiltration and its contribution and time delay to soil water at different depths were clarified, the influence of water infiltration on soil dissolved carbon at different depths was clarified, and the vertical transport process of soil water and dissolved carbon in the high cold region and its response to the rainfall were revealed. The results deepen the understanding of the vertical migration of carbon and water in the alpine meadow ecosystem, and have important scientific significance for understanding the water resources utilization and carbon neutrality strategy in the Tibetan Plateau under the background of climate change. The main conclusions are as follows:
(1) The average precipitation and the average soil volumetric water content of Qianhuli small watershed in 2022 and 2023 growing seasons (June to October) are 377.4mm and 15.74%, respectively, increasing first and then decreasing with the change of air temperature and the increase of soil depth. In 2022 and 2023, a total of 195 precipitation events will occur, and the precipitation of 0~5 mm, 5~10 mm, 10~15 mm and more than 15 mm account for 24.51%, 18.89%, 14.41% and 42.19% of the total precipitation, respectively. The average volume water content of 10 cm, 30 cm and 75 cm soil in the vertical profile was 10.24%, 30.64% and 6.34%, respectively. The soil water content first increased and then decreased with the soil depth, and the soil water content at 30 cm depth was the highest. With the increase of temperature in the growing season, soil water content increased, which showed a relatively synchronous trend with the change of precipitation. In 2022 and 2023, the average values of stable isotopes of hydrogen and oxygen in precipitation are -35.41‰ and -6.69‰, respectively, and the average values of stable isotopes of hydrogen and oxygen in soil are -41.16‰ and -6.75‰, respectively. The distribution is relatively clustered, and the water supply is mainly precipitation, and it is also affected by the mixing of evaporation and other water sources.
(2) The response thresholds of soil water at 10 cm, 30 cm and 75 cm depth to precipitation in alpine meadow ecosystem were 3 mm, 15 mm and 17 mm, respectively. The response lag time was subject to soil depth and precipitation conditions, ranging from 1 to 3 days, and soil water sources at different depths were significantly affected by precipitation conditions. When the precipitation is less than 20 mm, the response of soil moisture at a depth of 10 cm to precipitation has a lag of about 2 days, while precipitation larger than 20 mm will continue to affect soil moisture 1 to 9 days after the occurrence, and the contribution rate of precipitation to the water in this layer is 10% to 32%. Soil water at 30 cm depth was affected by precipitation, pre-water content and water content in the upper soil, and the average response time was about 3 days when the precipitation was more than 15 mm. The response continued 3 to 11 days after the occurrence of precipitation greater than 20 mm. When continuous precipitation occurred, the soil moisture at 10 cm depth was the most responsive to the precipitation of the day, and could be recharged by 11.5%~46% of the precipitation, while the soil moisture at 30 cm depth was recharged by the previous precipitation at a higher proportion, ranging from 11% to 27%.
(3) The spatial and temporal distribution of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in different depths of alpine meadow ecosystem was obviously different. The average infiltration of DOC and DIC in 0~20 cm, 20~50 cm and 50~80 cm soil layers could reach 227.56% and 146.63% of their own content, respectively. -3.36% and 24.32%, 22.11% and 22.02%, the response characteristics of DOC and DIC infiltration to different precipitation conditions are different. The average soil DOC concentration in the growing season was 29.21 mg/L, and showed a trend of first increasing and then decreasing from June to September. In soil vertical profile, DOC concentration decreased with increasing soil depth. The average DIC concentration in soil during the growing season was 23.43 mg/L, and increased continuously from June to September. The content of DIC in vertical profile increased from shallow layer to deep layer. With the increase of precipitation and water infiltration, the DOC infiltration in 0~20 cm soil was positively correlated with the precipitation of 2 lag times (R² = 0.36). The DIC infiltration was significantly affected by precipitation DIC (R² = 0.52). The higher the precipitation, the more dissolved carbon input from 20~50 cm soil, the more DOC output and the less DIC output. The input of DOC and DIC in 50~80 cm soil was mainly affected by precipitation. DOC migrates from shallow layer to deep layer, DIC is affected by water migration from top to bottom, and the soil can also receive DIC in dissolved carbonate.