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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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Keywords:
- Soil CO2 concentration /
- Deep soil /
- Precipitation event /
- Semi-arid area
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土壤作为陆地生态系统中最大的有机碳库[1], 30 cm以下有机碳储量占到土壤碳库的30%~75%[2]。与表层土壤相比, 尽管深层土壤(>30 cm)有机碳含量相对稳定, 但其矿化分解也不容忽视[3]。有研究指出深层土壤中CO2浓度更高[4], 并且以较快的速度通过土壤孔隙释放到大气中[5], 因此深层土壤CO2产生和排放的微小变动会显著影响陆地碳循环过程[1,6]。
土壤CO2浓度是土体内CO2产生和排放综合作用的结果[7], 由于温度、水分、微生物和底物等影响因素的垂直空间变异性[8-9], 深层土壤CO2浓度变化和表层土壤并不相同。随着深度的增加, 有机质含量和微生物生物量逐渐减少、土壤温度降低等原因导致深层土壤CO2产生较少, 但深层土壤CO2浓度却高于表层[8,10-11]。水分对土壤CO2浓度的影响较为复杂, 土壤干湿变化会强烈影响土壤有机碳矿化速率和CO2排放[12-14], 不仅影响土体内的CO2浓度, 也会影响其与大气中CO2交换[15-16]。研究表明, 0~10 cm处CO2产生量与土壤含水量呈正相关, 而在10~20 cm处CO2产生量与土壤含水量呈负相关[17]。除改变土壤水分状况外, 降雨不仅影响土壤CO2产生, 还可能阻断气体扩散通道, 导致土壤CO2浓度上升, 这一变化在土壤深层尤为明显[18]。Delsarte等[19]发现降雨导致表层和深层土壤CO2浓度均降低。Rachhpal等[20]研究表明降雨后, 表层和深层土壤CO2浓度升高。Fernandez-Bou等[21]和刘合满等[22]却认为表层和深层土壤CO2浓度变化在降雨事件中呈现相反的变化趋势。在干旱半干旱区, 降雨作为土壤水分的主要来源, 其多变性(降雨量、降雨强度等)对土壤CO2浓度的影响仍然存在很大的不确定性[22-23], 尤其深层土壤CO2浓度对降雨的响应尚不清楚。
本研究在田间原位条件下, 对10 cm、50 cm和100 cm深土壤CO2浓度、土壤温度和土壤水分进行高频率自动监测, 探究深层土壤CO2浓度的变化特征及其对降雨事件的响应和影响因素, 以期进一步了解降雨事件对深层土壤CO2浓度变化的作用机制, 为正确评估干旱区降雨变化对生态系统碳循环影响提供科学基础。
1. 材料与方法
1.1 试验地概况
试验地位于黄土高原南部陕西长武农田生态系统国家野外科学观测研究站(简称长武站, 107°40ʹE, 35°12ʹN), 海拔约1220 m, 属大陆性季风气候。平均温度9.1 ℃, ≥10 ℃积温为3029 ℃, 最低温度为−19.6 ℃, 最高温度为32.4 ℃; 1985—2020年平均降水量580 mm, 其中最高年份为954 mm, 最低年份为296 mm, 并且季节性分布不均, 7—9月份降水占年降水量的55%左右, 最高月份为237 mm。降雨入渗深度最深可达3 m, 地下水位50~80 m。无灌溉条件, 属典型的旱作雨养农业区。土壤类型为黑垆土, 母质是中壤质马兰黄土[24], 不同深度土壤理化性质见表1。
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 1.2 试验设计
黄土高原是优质苹果(Malus domestica)的适生区, 该区域苹果园面积已经超过120万hm2 [25]。基于此, 本研究以苹果园为研究对象, 探讨半干旱区深层土壤CO2浓度对降雨事件的响应。所选苹果园建于2000年, 面积1000 m2, 种植品种为‘红富士’, 株行距为3 m×4 m, 呈南北走向, 平均树高3.5 m, 多年平均产量为42 000 kg∙hm−2 [26]。无灌溉条件, 每年11月施用基肥(氮肥 100 kg∙hm−2和磷肥 375 kg∙hm−2), 次年7月追施氮肥(100 kg∙hm−2)。一般春秋两次修剪, 9月份采摘, 果树生长状况良好, 无病虫害。
在果园中心选取两株长势均匀、位置相邻且不同行的果树, 取两株果树之间的中心位置作为首个点位, 以该点位为基准, 向正南、正北方向6 m再各选取1个点位, 共计3个点位, 各点位中心点距离两侧果树均为2 m。每个点位并排设置两个100 cm测坑, 分别用于监测10 cm、50 cm和100 cm土层的土壤温度、水分(西侧测坑)和CO2浓度(东侧测坑), 共设置6个测坑。测坑内安装仪器后回填压实, 实时监测各要素变化情况。监测点布设情况如图1所示。
1.3 土壤温度、水分、CO2浓度及降水的测定
本研究开展于2019—2021年, 通过在测坑中安装土壤水分和温度电导率传感器CS655 (campbell, 美国)、数据采集传送器CR1000X (campbell, 美国)监测记录各土层土壤温度(℃)、土壤含水量(%)的逐时变化情况; 在土壤CO2测坑中水平安装GMP343_SS探头(Vaisala, 芬兰)监测各土层CO2浓度(μmol∙mol−1)的逐时变化情况。上述仪器均依靠太阳能供电, 利用太阳能板TR-SP50Z1 (华益瑞, 中国)、蓄电池TR-J200 (华益瑞, 中国)、防水机箱ENC14/16 (campbell, 美国)做好蓄电防水工作, 确保电量充足和数据采集的稳定性。
降雨和气温由长武站自动气象站实时观测, 自动记录每小时降雨量(mm∙h−1)和气温(℃)。本研究对降雨事件进行以下判定: 降雨发生前24 h无降水, 且降雨停止后5 h没有降雨作为判定标准。参考国家气象局规定(http://www.cma.gov.cn)对降雨事件进行划分: 降雨量在10 mm以下为小雨, 10~25 mm为中雨, 25 mm以上为大雨。测定时间为春季(4—6月)、夏季(7—9月)、秋季(10—11月) 3个季节。为了探究降雨变化对各土层土壤CO2浓度的影响, 在夏季(雨季)选取小雨(8 mm)、中雨(15.6 mm)、大雨(31.6 mm) 3个典型的降雨事件进行深入分析, 小雨、中雨和大雨分别选取降雨前1 d至降雨停止后3 d、5 d和7 d确保各因素对降雨响应的完整性。
1.4 土壤微生物量碳测定
用“S型采样法”在果园中心选取5颗长势良好、无病虫害的标准果树。以树主干为中心, 沿三等分圆半径方向取0.5 m、1.0 m和2.0 m处为采样点, 在每个采样点垂直向下0.1 m、0.5 m和1.0 m处取土, 并将同一颗树、同一土层的3个土样取等量混匀装袋。将土样冷冻处理, 用于测定土壤微生物量碳(氯仿熏蒸硫酸钾浸提法)。
1.5 数据处理
1.5.1 气体扩散系数
基于不同试验条件和研究目的, 有研究者综述了不同土壤扩散系数模型的优劣[27]。考虑本研究为田间原位监测试验, 土壤相对干燥, 充气孔隙度为0.11~0.45, 故选取Moldrup-2000模型计算气体扩散系数[28]:
$$ \frac{{D}_{S}}{{D}_{0}}=\varepsilon $$ (1) $$ {D}_{0}={D}_{a0}{\left(\frac{T}{{T}_{0}}\right)}^{1.75}\left(\frac{{P}_{0}}{P}\right) $$ (2) 式中: Ds为深度s处CO2的扩散系数(m2∙s−1), D0为CO2在自由大气中扩散系数(m2∙s−1);
$ {\varepsilon } $ 为CO2在土壤中的相对扩散系数; Da0为T0 (293 K)、P0 (标准大气压, 1.31×105 Pa) 下CO2在大气中的扩散系数(1.47×10−5 m2∙s−1); T、P为实际测量时温度(K)和气压(Pa)。$$ \varepsilon =\frac{{(\varphi -\theta )}^{2.5}}{\varphi } $$ (3) $$ \varphi =1-\frac{{\rho }_{\mathrm{b}}}{{\rho }_{\mathrm{s}}} $$ (4) 式中:
$\varphi$ 为土壤孔隙度(cm3∙cm−3);$ {\rho }_{\mathrm{s}} $ 为土壤比重, 本研究中该值为2.65 g∙cm−3;$ {\rho }_{\mathrm{b}} $ 为土壤容重;$ \theta $ 为土壤体积含水量(cm3∙cm−3)。1.5.2 数据分析
利用Excel 2010对原始数据进行整理、筛选和初步分析, 采用Origin 2018软件制作相关的基础图件。
2. 结果与分析
2.1 不同土层温度和水分的变化特征
土壤温度受气温影响, 表现出明显的季节特征。春季土壤温度逐渐升高, 夏季(8月中旬)达到峰值, 秋季随气温下降而逐渐降低(图2a)。观测期内, 10 cm、50 cm、100 cm土壤温度最高可达28.4 ℃、24.1 ℃和21.4 ℃, 最低至4.6 ℃、7.6 ℃和8.4 ℃, 均值为18.2 ℃、17.1 ℃和16.0 ℃。各土层温度存在显著性差异(P<0.05), 在温度上升期表现为100 cm土层<50 cm土层<10 cm土层, 到达峰值后转为10 cm土层<50 cm土层<100 cm土层。
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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试验期间(2019—2021年)共发生降雨事件23次, 小雨(<10 mm)发生频次最多, 共计13次, 占总降水频次的56%, 中雨(10~25 mm)次之, 占总降水频次的26%, 大雨(>25 mm)占比18% (图2b, 表2)。10 cm土壤水分对降雨的响应最为敏感, 雨后土壤含水量最高可达雨前的两倍之多; 50 cm和100 cm处土壤含水量对降雨的响应相对迟缓, 在降雨事件中土壤水分增加量不超过11% (图2c)。10 cm、50 cm和100 cm处土壤含水量最高为31.7%、39.1%和35.0%, 最低至8.7%、30.1%和23.8%, 均值为17.2%、33.7%和27.4%。土层间土壤含水量差异显著(P<0.05), 表现为10 cm土层<100 cm土层<50 cm土层 (图2c)。
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 2.2 不同土层CO2浓度的变化特征
季节尺度上, 10 cm、50 cm和100 cm处土壤CO2浓度与土壤温度有相似的季节特征和土层间的差异, 即在春季逐渐升高, 于8月份达到全年峰值, 秋季持续下降(图2d)。春末时10 cm、50 cm和100 cm处CO2浓度为春初的2.8倍、2.6倍和2.6倍; 夏季各土层CO2浓度峰值可达1.20×104 μmol∙mol−1、1.56×104 μmol∙mol−1和1.67×104 μmol∙mol−1; 而与CO2浓度峰值相比, 秋季分别降低62%、58%和53%。但与土壤温度不同, 土壤CO2浓度呈现出随着深度增加逐渐上升的趋势, 10 cm、50 cm、100 cm处CO2浓度均值为0.66×104 μmol∙mol−1、0.87×104 μmol∙mol−1和1.04×104 μmol∙mol−1, 50 cm、100 cm处CO2浓度分别为10 cm处的1.3倍和1.6倍。
晴天时, 10 cm、50 cm和100 cm处土壤CO2浓度均有显著的日变化特征, 其动态变化存在明显的单峰趋势, 并与气温呈相反的变化模式(图3)。10 cm处土壤CO2浓度还与土壤温度的变化趋势基本一致(图3a), 均表现为先降低后升高, 13:00左右达全天最低值, 而在50 cm和100 cm处, 土壤温度对土壤CO2浓度变化的影响不大(图3b, c)。雨天时, 各土层土壤CO2浓度变化趋于平缓, 日变化幅度减小。10 cm处土壤CO2浓度变化趋势与晴天时基本一致(图3d), 而50 cm、100 cm处土壤CO2浓度未出现单峰变化(图3e, f)。
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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)2.3 不同土层CO2浓度对降雨事件的响应
土壤CO2浓度对降雨量<10 mm的小雨事件无明显响应。10~25 mm的中雨可以导致10 cm处土壤含水量从32.1%上升至35.7%, 土壤CO2浓度降低5%; 50 cm处土壤含水量和CO2浓度的响应则较为迟缓。>25 mm的大雨事件发生时, 10 cm处土壤含水量仅有10.5%, 该处土壤CO2浓度随着水分上升增加了30%, 表现出明显的激发效应; 当10 cm处土壤含水量升高至19.0%, 持续降雨导致土壤CO2浓度降低。大雨导致50 cm、100 cm土壤含水量从32.0%、24.7%上升至39.1%、35.0%, 土壤CO2浓度分别降低16.3%、10.9%。大雨事件中, 10 cm、50 cm、100 cm土壤CO2响应时间为降雨开始后9 h、91 h和121 h, 土壤含水量和土壤温度对降雨的响应存在类似的滞后现象(图4)。
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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 layers3. 讨论
3.1 不同土层CO2浓度对水分的响应
土壤CO2浓度取决于产生和传输的共同作用。虽然表层土壤根系密度大、微生物活性高, 但CO2能快速排放至大气中, 因此表层土壤CO2浓度低。一般而言, 深层土壤中的微生物量通常比表土低1~2个数量级[29], 氧气浓度也会随着深度增加逐渐降低, 深层土壤生物和根系的生长环境较差[30], 导致深层土壤CO2产生较少。本研究发现深层土壤微生物量显著低于表层(10 cm vs. 50 cm vs. 100 cm: 125.44 mg∙kg−1 vs. 45.92 mg∙kg−1 vs. 12.50 mg∙kg−1)。因此, 深层土壤CO2浓度与微生物关系不大。随着土层加深, 土壤中CO2扩散性降低可能是导致深层CO2浓度升高的主要原因。深层土壤质地紧实(容重=1.30 g∙cm−3), 孔隙度较小, 土壤CO2扩散系数(D)仅为表层土壤的1/8~1/4 (D10 cm=22.6×10−7 m2∙s−1、D50 cm=2.7×10−7 m2∙s−1、D100 cm=6.7×10−7 m2∙s−1), 导致深层土壤CO2气体的累积并表现为浓度升高[31]。喀斯特[23]、土[32]和森林[33]土层中CO2浓度变化的相关研究也得到了相似的结果。
不同土层CO2浓度因其土壤孔隙含水量增加而呈降低趋势, 但关系复杂。表层土壤含水量因降雨波动剧烈, 相应地土壤CO2浓度波动范围也较大, 随着土壤含水量升高, 土壤CO2浓度呈降低趋势(图5); 随着深度的增加, 土壤含水量波动范围(32%~35%)变小, CO2浓度波动范围(4000~16 700 μmol∙mol−1)加大(图2), 土壤CO2浓度随着水分升高而降低的相关性得到加强; 当达到100 cm土层深度时, 土壤含水量基本稳定在24%~30%, 因大雨时水分入渗到深层后土壤水分才在短时间内出现变化, 相应地土壤CO2浓度才会出现剧烈变化, 但短时间内出现的水分和土壤CO2浓度变化并不存在简单的线性关系。其中原因需要进一步的田间监测和研究。
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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 depths3.2 降雨事件对深层土壤CO2浓度的影响
降雨影响土壤CO2浓度, 但不同土层CO2浓度变化并不相同[34]。大雨初期(前3 d), 随着土壤由干变湿, 10 cm处土壤CO2浓度迅速增加并达到峰值(图4g)。干湿交替引起团聚体破坏(物理学说)或土壤水分引起的微生物群落结构和活性变化促进了土壤CO2产生(生理学说)[2,35]。与10 cm处激发效应不同, 在50 cm和100 cm处由于雨前土壤含水量(W)较高(Wpre-50 cm=32%, Wpre-100 cm=24.7%), 降雨后反而抑制CO2的产生(图6e, f)。深层土壤含水量一般高于表层, 降水导致的深层土壤含水量的进一步升高, 降低了土壤通透性和土壤中O2的供应, 使得好氧微生物的活性受到抑制[36]; 其次, 水分过高还会阻碍土壤溶液中可溶性有机碳(DOC)的扩散, 降低微生物可利用的DOC含量[37-38]。此外, 尽管表层土壤出现了CO2升高的激发效应, 但当土壤含水量超过19%时, 激发效应减弱。这可能与土壤孔隙逐渐被水分填充, 土壤处于厌氧环境中, 微生物呼吸和根系代谢受到抑制有关[39-40]。
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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 layersThe 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.大雨导致10 cm处CO2浓度升高还与CO2扩散系数降低有关。本研究发现降雨导致CO2扩散系数降低4%~47% (图6)。水分升高阻碍土壤气体向大气中扩散, 从而使得扩散系数降低[23]。但土壤CO2浓度并不总是随着CO2扩散系数的降低而升高, 大雨事件中100 cm处气体扩散系数和土壤CO2浓度均呈降低趋势(图6f)。除此之外, 半干旱地区土壤CO2溶解也会影响其浓度变化。研究地土壤中碳酸盐含量为10.5%、pH值8.2[41], 这会显著影响土体内CO2气体的溶解和固存[42]。Maier等[15]认为入渗的雨水和大气中浓度较低的CO2保持平衡, 进入土壤后, 雨水会对土体内部浓度较高的CO2有稀释作用。而CO2溶解形成碳酸盐溶液所需时间远低于形成碳酸钙的时间
$ \left(\text{CaC}{\text{O}}_{\text{3}}\text{+ C}{\text{O}}_{\text{2}}\text{+}{\text{H}}_{\text{2}}\text{O}{\Leftrightarrow}{\text{Ca}}^{\text{2+}}\text{+}2\mathrm{H}\mathrm{C}{\mathrm{O}}_{3}^{-}\right) $ , 这也可能是降雨事件中导致土壤CO2浓度降低的重要原因。4. 结论
在半干旱区, 78%的降雨事件可以引发10 cm处CO2浓度变化, 降雨量为10~25 mm、>25 mm的降雨事件分别导致50 cm和100 cm处土壤CO2浓度降低, 响应时间各自滞后91 h、121 h。降雨对土壤CO2浓度的影响取决于土壤含水量状况, 土壤由干变湿时, 降雨可以对10 cm土壤CO2浓度产生正激发效应, 而在含水量较高的深层土壤, 则产生负激发效应。
致谢: 感谢陕西长武农田生态系统国家野外科学观测研究站对本研究的支持。
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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
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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)
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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
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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
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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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1. 方啸宇，徐文清，刘文，李少楠，李文涛，陆爱华，房经贵. 巨峰葡萄9种元素缺素症的研究. 核农学报. 2024(06): 1196-1204 . 
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