The legacy effects of soil types on carbon content are erased by extreme flooding stress in a water-level drawdown zone

Soil carbon dynamics are closely related to pedologic properties and highly variable among different soil types, however, it is not clear if the effects of soil types on carbon storage can be erased by a continuous environmental stress. Periodic flooding, the dominant environmental stress on natural riparian habitats, greatly regulates the biogeochemical cycles of carbon. To reveal how flooding stress affects carbon storage within different soils, here, we have examined soil types' effects on carbon storage along a flooding gradient in the riparian zones of the Three Gorges Reservoir. The two-way ANOVA analysis was applied to measure the effects of soil type, flooding stress, and their interactions on aggregate proportion, organic carbon fraction, carbon concentration, and content in aggregates and bulk soils. The partial least squares path model was used to uncover the potential mechanisms of flooding stress affecting carbon storage for different soils. The results presented that the topsoil of the riparian zone of the Three Gorges Reservoir holds exceeding 3.95 Tg of carbon. Anthorosols, Luvisols, and Regosols stored 351.02, 275.50, 1349.50 Gg C, respectively. Flooding stress was found to positively affect C content for Anthrosols and Regosols with total effect sizes of 0.52 and 0.59, respectively. However, flooding stress had a negative impact on C content in Luvisols. In addition, the effect sizes of soil types on C content were alleviated by the strong flooding stress, and the effect size at the control and weak stress levels were higher than that at strong and intermediate stress levels. The original heterogeneousness of soil physical properties within different soils was homogenized by the extreme flooding stress, which can be indicated by aggregate proportion and particulate organic carbon.

Automated summary

Soil types have an impact on carbon storage, but it is uncertain whether continuous environmental stress can mitigate the effects of soil types. We examined the effects of flooding stress on carbon storage in different soil types in the riparian zones of the Three Gorges Reservoir and found that flooding stress has different effects on carbon storage in different soil types.