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土壤水分是土壤CO2产生和传输的主要控制因子,对其进行研究可以更好的理解土壤水分对土壤碳通量的影响。梯度法是估算土壤CO2扩散通量的一种常见方法,该方法利用菲克第一定律计算土壤CO2扩散通量,其关键参数是气体扩散系数(DP)和CO2浓度梯度。本实验用放置在恒温室内的土柱研究土壤水分变化对梯度方法估算土壤表面CO2扩散通量的影响,利用Millington-Quirk模型对气体扩散率进行模拟。结果表明,土壤CO2浓度随着土壤深度的增加而增加,15 cm处的土壤CO2浓度平均值(1991.8μmol mol-1)明显大于5 cm处土壤CO2浓度平均值(1495.1μmol mol-1),土壤水分与两层土壤CO2浓度变化趋势具有一致性。在土壤温度保持相对稳定的情况下,CO2通量随体积含水量的变化而变化,在干燥或含水量很高的条件下土壤CO2通量较低,接近田间持水量时CO2通量最大;在大多数情况下,梯度法和动态气室法测得的土壤碳通量具有较好的一致性。
Soil moisture is the main controlling factor for the production and transmission of soil CO2. Studying it can better understand the impact of soil moisture on soil carbon flux. Gradient method is a common method for estimating soil CO2 flux. The method uses Fick’s first law to calculate soil CO2 flux. The key parameters are gas diffusion coefficient (DP) and CO2 concentration gradient. In this experiment, we used soil column placed in a constant temperature chamber to study the effect of soil moisture change on estimating the diffusive flux of CO2 on the soil surface by gradient method. The gas diffusion rate was simulated by Millington-Quirk model. The results showed that the soil CO2 concentration increased with the increase of soil depth. The average value of soil CO2 concentration at 15 cm (1991.8 μmol mol-1) was significantly higher than that at 5 cm (1495.1 μmol mol-1) The trend of the change of CO2 concentration between water and soil is consistent. Under the condition of relatively stable soil temperature, the CO2 flux changes with the change of volumetric water content, and the soil CO2 flux is lower under dry or high water content conditions, In most cases, the soil carbon fluxes measured by the gradient method and the dynamic gas chamber method have good agreement.