The effect of water repellency on the short-term release of CO2 upon soil wetting
The effect of water repellency on the short-term release of CO2 upon soil wetting
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DOI：
10.1016/j.geoderma.2020.114481
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发表时间：
2020-10
期刊：
影响因子：
6.1
通讯作者：
Carmen Sánchez-García;S. Doerr;Emilia Urbanek
中科院分区：
文献类型：
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作者：
Carmen Sánchez-García;S. Doerr;Emilia Urbanek
干燥土壤再润湿后观察到的二氧化碳 (CO2) 峰值（称为“桦木效应”）可能对土壤总碳 (C) 排放量产生重大影响，然而，这种突然二氧化碳释放的确切机制和时间仍不清楚。施水量和前期干旱持续时间被认为是影响CO2峰值大小的主要因素，但前期由土壤含水量低引起的土壤润湿性变化也可能是一个重要因素。我们研究了土壤斥水性（SWR，通过水滴渗透时间测试评估）对不同水量的干燥土壤润湿时CO2短期释放的影响。实验是在实验室条件下进行的，使用来自英国南威尔士两个地点的均质且高压灭菌的土壤，土壤处于可湿性和极防水状态。使用样品上方和下方的室测量 CO2 流出量。润湿后，由于通过优先路径快速渗透，防水土壤中的 CO2 流出量降低了 10 倍，土壤中仅保留少量水（最多 10%）。总 CO2 流出量与渗透后保留在土壤中的水成正比，表明 CO2 的释放仅从土壤的有限孔隙空间中发生。快速的二氧化碳释放表明化学或生化过程，而不是微生物呼吸，是本研究中二氧化碳流出的主要来源。释放的部分二氧化碳被输送到底部室，在自然条件下可以增强地下土壤中气体的截留。这项研究表明，SWR 导致的充满水的孔隙空间的变化显着减少了润湿时的 CO2 流出，并表明 SWR 可能是研究和预测 C 通量的关键因素。
The spike in carbon dioxide (CO2) observed after rewetting of dry soils, known as the ‘Birch effect’, can contribute substantially to total soil carbon (C) emissions, however, the exact mechanisms and timings underlying this sudden CO2release remain unclear. The amount of applied water and duration of the previous dry period are considered the main factors affecting the magnitude of the CO2peak, but the preceding change in soil wettability, triggered by low soil water content, could also be an important contributor.We investigated the effect of soil water repellency (SWR, assessed by water drop penetration time test) on the short-term release of CO2upon wetting of dry soils with different water quantities. The experiments were conducted under laboratory conditions using homogeneous and autoclaved soil from two locations in South Wales (UK) in both wettable and extremely water-repellent states. The CO2efflux was measured using chambers above and below the samples. Upon wetting, CO2efflux was up to 10 times lower in water-repellent soils as a result of rapid percolation through preferential pathways, with only a small amount of water (up to 10%) retained in the soil. Total CO2efflux was proportional to the water retained in the soil after infiltration, suggesting that the release of CO2occurred only from limited pore-spaces of the soil. The quick CO2release suggests that chemical or biochemical processes, rather than microbial respiration, is the main source of CO2efflux in this study. Part of the CO2released was transported to the bottom chamber, which under natural conditions could enhance the entrapment of gas in the subsoil. This study shows that alterations in the water-filled pore-space as a result of SWR significantly reduced the CO2efflux upon wetting and suggests that SWR could be a key factor when investigating and predicting C fluxes.