Relationship between soil carbon sequestration and the ability of soil aggregates to transport dissolved oxygen
Relationship between soil carbon sequestration and the ability of soil aggregates to transport dissolved oxygen
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DOI：
10.1016/j.geoderma.2021.115370
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发表时间：
2021-12
期刊：
影响因子：
6.1
通讯作者：
Xiaoxian Zhang;A. Gregory;W. R. Whalley;K. Coleman;A. Neal;A. Bacq-Labreuil;S. Mooney;J. Crawford-J.
中科院分区：
文献类型：
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作者：
Xiaoxian Zhang;A. Gregory;W. R. Whalley;K. Coleman;A. Neal;A. Bacq-Labreuil;S. Mooney;J. Crawford-J.
土壤有机碳（SOC）的稳定性不是由其分子复杂性或粘粒吸附控制的，而是由其物理化学保护作用控制的，包括团聚体中的吸附和有机-无机结合体的吸附-沉淀。缺氧条件下有机无机复合体和吸附态SOC的微生物溶解是碳循环的重要途径，但被大多数碳模型所忽视。据报道，有机-无机结合体在有氧条件下形成，在厌氧条件下可能会丢失，因此SOC与团聚体运输溶解氧的能力之间应该存在正相关关系。我们开发了一个模拟模型来验证这一点，使用两个长期实验的土壤结构数据，自然产生了SOC梯度：一个是1843年建立的冬小麦实验，比较不同施肥对冬小麦产量的影响，另一个是1948年建立的ley-耕地实验，调查种植制度变化对生态产量的影响。使用X射线计算机断层扫描仪扫描来自两个实验的不同处理的聚集体，以使用孔隙尺度模型来模拟氧运输。我们比较了所有聚集体的孔隙度和扩散系数，并将它们与两个实验测得的SOC联系起来。67年或172年前的农业实践改变了土壤团聚体（<2 mm）的内部结构，土壤有机碳的增加与团聚体输氧扩散系数呈正相关。然而，扩散系数随着SOC渐近地增加，当SOC超过阈值时趋于平稳。我们还发现，在化学施肥的土壤团聚体的扩散系数与其孔隙度的趋势大致以相同的方式，偏离与其他非作物处理或施肥与农家肥。
A key finding in soil carbon studies over the past decade is that soil organic carbon (SOC) stabilization is not controlled by its molecular complexity or adsorption to clay, but by its physicochemical protection including occlusion in aggregates and sorption-precipitation with organo-mineral associations. The organo-mineral complexes and the adsorbed SOC can be dissolved microbially under anoxic conditions, which is an important pathway in carbon cycle but has been overlooked by most carbon models. As organo-mineral associations are reported to form in aerobic conditions and can be lost under anaerobic conditions, there should be a positive correlation between SOC and ability of the aggregates to transport dissolved oxygen. We develop a simulation model to test this using soil structural data from two long-term experiments which naturally created a SOC gradient: One is a winter wheat experiment established in 1843 to compare the effects of different fertilizations on the yield of winter wheat and the other one is a ley-arable experiment established in 1948 to investigate the consequence of cropping system changes for ecological yield. Aggregates from different treatments on the two experiments were scanned using X-ray Computed Tomography to simulate oxygen transport using a pore-scale model. We compared porosity and diffusion coefficient of all aggregates and linked them to SOC measured from the two experiments. The agronomic practice changes which occurred 67 or 172 years ago substantially reshaped the intra-aggregate structure (<2 mm), and the accrual of SOC is positively correlated with diffusion coefficient of the aggregates to transport oxygen. However, the diffusion coefficient increases with SOC asymptotically, plateauing when SOC exceeds a threshold value. We also found the diffusion coefficient of the aggregates in chemically fertilized soils trended with their porosity approximately in the same way, deviating from those for other non-cropped treatments or fertilized with farmyard manure.