Soil erosion progression under rill and gully erosion processes and its effect on variations of mechanisms controlling C mineralization ratio

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The progression of water erosion patterns from rill to gully erosion significantly affects the level of soil aggregate degradation, and thereby stimulates variations in the biochemical mechanisms controlling the OC mineralization ratio. These conditions can affect the exchange of carbon from biosphere to atmosphere. We examined the effect of erosion progression on the physical and biochemical soil properties controlling the C mineralization ratio within the original soils eroded by the rill and gully processes. Aggregate size distribution, geometric mean diameter (GMD), mean weight diameter (MWD), exchangeable cations, dissolved organic carbon (DOC), microbial respiration, and microbial biomass carbon (MBC) were measured. Despite the greater proportion of the labile components of OC in the rill soils, the C mineralization ratio exhibited lower values in these soils compared with the gully soils. A higher value of GMD, MWD, and exchangeable cations were observed in the rill soils. The results of the stepwise multiple regressions illustrated that the higher C mineralization ratio in the gully soils is significantly positively correlated with DOC and microbial respiration. By contrast, the lower C mineralization ratio in the rill soils was found to be significantly negatively related to the GMD, DOC, and MWD. These variations may be attributed to the effects of the increasing soil aggregate stability on lower vulnerability of labile organic carbon to microbial mineralization. The lower transport capacity of the rill erosion process causes a less loss of SOC and micro-aggregate compared with the gully erosion process. The labile fractions of SOC could bond with clay fractions and exchangeable cations to contribute toward the formation of soil aggregates, encouraging higher resistance of DOC against microbial mineralization in the rill soils. This conceptual approach of combining our field survey data with an empirical model aids in a better understanding of the biochemical mechanisms controlling the C mineralization ratio under the progression of soil erosion.