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摘要: 降雨是干旱半干旱地区土壤CO2产生、传输或扩散的重要影响因素, 并进一步影响土壤和大气中的CO2浓度。目前大量研究集中在地表CO2通量变化与降雨的关系, 深层土壤有机碳储量巨大, 但深层土壤CO2浓度变化对降雨事件的响应机制尚不清楚。本研究通过对10 cm、50 cm和100 cm处土壤CO2浓度进行原位连续监测, 分析不同深度土壤CO2浓度对降雨事件的响应过程及其影响因素。结果表明: 试验期间, 78%的降雨事件能迅速引起10 cm处土壤CO2浓度发生改变, 且随着降雨量增大, 土壤CO2浓度发生变化的深度逐渐增加。当降雨量在10~25 mm时, 50 cm处土壤CO2浓度在91 h后降低; 降雨量>25 mm时, 100 cm处土壤CO2浓度在121 h后降低。当土壤由干变湿时, 降雨量>25 mm的降雨事件促进10 cm处土壤CO2浓度升高30%后开始降低, 而50 cm和100 cm处土壤CO2浓度随水分升高分别降低16.3%和10.9%。在半干旱区, 当土壤含水量较低时, 降雨可以对10 cm处土壤CO2浓度变化产生短暂的正激发效应, 而深层土壤含水量往往高于田间持水量, 水分升高会导致该处土壤CO2浓度降低。降雨对不同深度土壤CO2浓度变化的影响存在差异, 这在很大程度上取决于土壤含水量状况。Abstract: In arid and semi-arid areas, soil moisture strongly influences the balance between respiration and diffusion, altering soil CO2 concentration and surface flux. Numerous studies have focused on the relationship between surface soil CO2 flux changes and rainfall events. Subsoil carbon constitutes a large fraction of the total carbon stock, but it is unclear how rainfall events influence subsoil CO2 concentration dynamics. We continuously monitored CO2 concentrations at 10, 50, and 100 cm in the soil profile from 2019 to 2021, and analyzed the various responses of subsoil CO2 concentration to rainfall events. In this study, soil temperature showed apparent seasonal characteristics. As the air temperature changed, the soil temperature of different depths also changed from 100 cm < 50 cm < 10 cm to 10 cm < 50 cm < 100 cm. The soil moisture content of different layers was in the order of 10 cm < 100 cm < 50 cm, and a significant fluctuation was found at 10 cm. The soil CO2 concentration gradually increased with the increase of the depth in the order of 10 cm < 50 cm < 100 cm, with mean values of 0.66×104, 0.87×104, and 1.04×104 μmol∙mol−1, respectively. On sunny days, the soil CO2 concentrations at 10, 50, and 100 cm showed apparent diurnal variations and could be expressed as a single-peak curve. However, rainfall events significantly affected the change trends of CO2 concentrations. Approximately 78% of the rainfall events quickly altered the soil CO2 concentration in 10 cm layer. When the rainfall amount was exceeded 25 mm, the CO2 concentration at 50 and 100 cm decreased after 91 and 121 hours. When the soil moisture status changed from drying to wetting phases under rainfall events, > 25 mm precipitation promoted an increase in soil CO2 concentration at 10 cm by 30% which then began to decrease. The soil CO2 concentrations at 50 and 100 cm decreased by 16.3% and 10.9%, respectively, with an increase in soil moisture. In arid and semi-arid areas, rainfall negatively affects the changes in soil CO2 concentration at 10 cm depth under lower soil moisture content. This is because the decrease in gas diffusivity led to an increase in CO2 concentration. Soil CO2 concentrations at 50 and 100 cm depths decreased under rainfall events, although the soil moisture was higher than the field capacity. This was caused by the high soil moisture content, which inhibited microbial respiration. The responses of soil CO2 concentration at different depths to rainfall differed and largely depended on the soil moisture content.
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Key words:
- Soil CO2 concentration /
- Deep soil /
- Precipitation event /
- Semi-arid area
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图 2 试验期间土壤CO2浓度、土壤温度和土壤含水量变化
Figure 2. Variations of soil CO2 concentration, soil temperature and soil moisture during the experiment
图 3 晴天(左侧图a, b, c)和雨天(右侧图d, e, f)气温和不同土层土壤温度、CO2浓度的变化
Figure 3. Variations of air temperature, soil temperature and soil CO2 concentration in different soil layers under different weather conditions (the left figures are sunny days; the right figures are rainy days)
图 4 不同降水事件对10 cm、50 cm和100 cm深土壤CO2浓度的影响
小雨的降雨量为10 cm以下, 中雨的降雨量为10~25 cm, 大雨的降雨量为大于25 cm。pre-指降雨前, post-指降雨后, 其后数字为天数。The precipitation of light rain, moderate rain and heavy rain are <10 cm, 10−25 cm and >25 cm. pre- means before rainfall, post- means after rainfall, the numbers following them are number of days.
Figure 4. Effect of different precipitation events on soil CO2 concentration of 10 cm, 50 cm and 100 cm soil layers
图 5 不同深度土壤CO2浓度和土壤含水量的关系
Figure 5. Relationship between soil CO2 concentration and soil moisture in different soil depths
图 6 不同降水事件对对10 cm、50 cm和100 cm深土壤CO2扩散系数的影响
小雨的降雨量为10 cm以下, 中雨的降雨量为10~25 cm, 大雨的降雨量为大于25 cm。pre-指降雨前, post-指降雨后, 其后数字为天数。
Figure 6. Effect of different precipitation events on soil CO2 diffusivities in 10 cm, 50 cm and 100 cm soil layers
The precipitation of light rain, moderate rain and heavy rain are <10 cm, 10−25 cm and >25 cm. pre- means before rainfall, post- means after rainfall, the numbers following them are number of days.
表 1 试验地不同深度土壤基本理化指标
Table 1. Soil basic physical and chemical indexes at different depths of the experimental site
土壤深度
Soil depth
(cm)容重
Bulk density
(g∙cm−3)充气孔隙度
Air-filled porosity
(cm3∙cm−3)pH 有机质
Organic matter
(g∙kg−1)全氮
Total N
(g∙kg−1)全磷
Total P
(g∙kg−1)全钾
Total K
(g∙kg−1)10 1.25 0.34 8.23 13.40 0.98 0.82 8.05 50 1.30 0.17 8.20 9.14 0.81 0.83 9.12 100 1.30 0.26 8.30 11.03 0.63 0.71 8.30 
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表 2 2019—2021年试验期间降水事件和土壤CO2浓度响应特征
Table 2. Characteristics of precipitation events and soil CO2 concentration response during the experiment from 2019 to 2021
降水类型
Precipitation type降水频次
Precipitation frequency占总降水频次比例
Proportion in total
precipitation frequency (%)土壤CO2浓度响应频次
Soil CO2 concentration response frequency10 cm土层
10 cm soil layer50 cm土层
50 cm soil layer100 cm土层
100 cm soil layer小雨 Light rain (<10 mm) 13 56 8 0 0 中雨 Moderate rain (10~25 mm) 6 26 6 2 0 大雨 Heavy rain (>25 mm) 4 18 4 4 3 总计 Total 23 100 18 6 3
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