摘要:为阐明不同层次土壤CO₂浓度日变化特征及对短时降雨的响应，以西藏东南部色季拉山急尖长苞冷杉（Abies georgei var. smithii）林为研究对象，在自然降雨条件下，分析短时降雨及水分再分布过程中各层次土壤CO₂浓度变化特征。结果表明：在0-60 cm层次内，土壤CO₂浓度随土壤层次的加深而显著增加（P < 0.01），二者之间呈显著对数函数关系（R=0.9764，P < 0.01）；短时降雨脉冲使表层5 cm土壤CO₂浓度显著下降，而10 cm层次土壤CO₂浓度显著增加；在降雨和水分再分布阶段，5 cm与10 cm层次土壤CO₂浓度之间极显著负相关，10、20、40 cm和60 cm之间均呈极显著正相关（P < 0.01）；5 cm层次土壤含水量显著影响0-60 cm剖面CO₂浓度，降雨阶段，二者之间极显著线性正相关（P < 0.001），而水分再分布阶段，二者之间符合极显著幂函数负相关（P < 0.001）。即降雨引起表层土壤含水量的快速增加，显著提高土壤剖面CO₂浓度，而降雨停止后，有利于土壤CO₂向土表的释放；土壤温度和含水量对CO₂浓度的影响效应在各层次之间表现不一致，除40 cm均为正效应外，其他各层均表现为相反的影响效应。这些结果表明，短时降雨使各层次土壤含水量增加，减少土壤表面CO₂释放量，使下层土壤体系中CO₂浓度升高，在分析土壤CO₂通量时间变化时，应考虑短时降雨对不同层次土壤CO₂的影响。



Abstract:Soil respiration is an important ecological process in which CO₂ from different depths of the soil is transported to the soil surface and released to the atmosphere. The CO₂ production and diffusion rates at different depths in the soil significantly affect the CO₂ flux from the soil surface. Rainfall is a frequent weather event that causes an increase in the soil water content (SWC), and temperature changes induce dramatic variations in soil CO₂ production and transport. To clarify diurnal variations in soil CO₂ concentrations and the response to short-term rainfall, we selected Sejila Mountain in Southeastern Tibet as a model area. Under natural rainfall conditions, the characteristics of abies georgei var smithii forest soil CO₂ concentrations at different depths were analyzed. The results showed that the soil CO₂ concentration increased with soil depth in the following order 60 cm > 40 cm > 20 cm > 10 cm > 5 cm. Mean values were 5365, 5304, 4990, 4335 and 4179 μmol/mol, respectively. There was a significant logarithmic relationship between the CO₂ concentration and the soil depth, given by y=531.1lnD + 3274 (R=0.9764,P=0.004). The soil CO₂ concentrations at 5 cm and 10 cm showed obvious diurnal variations, and could be expressed as a single-peak curve, while diurnal variations at 20 cm, 40 cm and 60 cm were very small. Short-term rainfall significantly affected the CO₂ concentrations in the 5 cm and 10 cm soil layers; the CO₂ concentration in the 5 cm soil layer decreased from 4196 μmol/mol to 4176 μmol/mol at the rainfall stage, and the CO₂ concentration in the 10 cm soil layer increased significantly from 4252 μmol/mol to 4354 μmol/mol. But there was a significant increase in CO₂ in the 5 cm soil layer and a decreased in CO₂ in the 10 cm soil layer during soil water redistribution. Closure of the CO₂ transport channel by water may be an important mechanism governing the increase in the CO₂ concentration in soil layers below 5 cm. At the rainfall and water redistribution stage, there was a significantly negative correlation between the CO₂ concentrations at 5 cm and 10 cm (P < 0.001), but a significantly positive correlation at 10 cm, 20 cm, 40 cm and 60 cm (P < 0.01). The SWC of the 5 cm layer had a significant effect on the CO₂ concentration in the 0-60 cm soil profile. There was a significant linear positive correlation (P < 0.001) between the SWC at 5 cm and the CO₂ concentration profile at the rainfall stage, while at the water redistribution stage it followed a power function model, and had a significantly negative correlation (P < 0.001). In other words, rainfall caused a rapid increase in the SWC of the 5 cm layer, which induced a significant increase in CO₂ in the 0-60 cm profile. The decrease in the SWC of the 5 cm layer at the water redistribution stage promoted a release of CO₂ from the soil into the atmosphere from the soil profile and caused the CO₂ content to decrease. The effects of soil temperature and SWC on the CO₂ concentration were not consistent among the different layers in the 0-60 cm soil profile, which showed that the other layers had the opposite effect, except at a depth of 40 cm. Overall, the results of this study indicate that the CO₂ emission flux induced in the soil by short-term rainfall decreased; however, the CO₂ concentration increased in the layer below 5 cm. This study suggests that diurnal variations in the CO₂ concentrations in the soil are affected by short-term rainfall.





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