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• The α-diversity of rare bacteria was greater in the depositional zones than in the eroding slopes. • The α-diversity of abundant bacteria between the eroding slopes and depositional zones showed no difference. • The community compositions of abundant and rare bacteria differed between the eroding slopes and depositional zones. • Abundant and rare species jointly maintained the stability of co-occurrence network in eroded ecosystem. • The α-diversity of rare bacteria showed closer linkage with SCCF than abundant bacteria. Elucidating the interaction between microorganisms and soil carbon cycling functionality (SCCF) in the eroded ecosystems, can improve our understanding of the mechanisms by which soil erosion and deposition affect soil organic carbon pool. Abundant and rare sub-communities are the integral components in driving SCCF. However, changes in abundant and rare sub-communities, as well as their contributions to SCCF, remain unclear in the eroded ecosystems. In this study, changes in abundant and rare sub-communities and their correlations with SCCF were comparatively explored with respect to soil erosion and deposition in the Loess Plateau. The α-diversity of rare sub-communities in the depositional zones was 4% higher than that in the eroding slopes, but there was no significant difference in α-diversity of abundant sub-communities between the eroding slopes and depositional zones. The compositions of abundant and rare sub-communities differed between the eroding slopes and depositional zones. Regarding the co-occurrence network of the eroded ecosystems, abundant sub-communities compared with rare sub-communities presented a higher degree and betweenness centrality; however, rare sub-communities possessed more frequent interactions with other species than abundant sub-communities, especially positive interactions. The α-diversity of abundant and rare sub-communities in ecological clusters showed positive links with SCCF. The link between α-diversity of abundant sub-communities and SCCF was weaker than that with rare sub-communities, which was related to the significant disparity in the abundance of functional genes involved in SCCF and the extent of functional redundancy between abundant and rare sub-communities in the eroded ecosystems. The functional difference of abundant and rare sub-communities in improving SCCF under soil erosion and deposition, is important for accurately assessing the effects of microbial communities on soil organic carbon pool in regions predominated with fragmented eroded landscapes. [ABSTRACT FROM AUTHOR]

• Enzyme activity decreased by erosion leading to an increase in the depositional plot. • Slope enhanced the difference in enzyme activity between the erosional and depositional plot. • Enzyme activity mitigated total soil CO 2 emission in the erosion-deposition plots. Soil C-acquiring enzymes are good indicators for the biological mechanism of soil nutrients and organic matter cycles. However, they have been used less frequently to assess the ecological stability and soil C cycle in eroding landscapes due to a lack of knowledge of the responses of C-acquiring enzyme activities to soil erosion and deposition. In the present study, a 3-year field simulation experiment was conducted to examine the variations in the activities of C-acquiring enzymes (β-1,4-xylosidase (βX), β-1,4-glucosidase (βG) and β-D-cellobiohydrolase (CBH)) from erosion-deposition plots with different slope gradients (5°, 10° and 20°) on the Loess Plateau in China (2016–2018). The activities of βX, βG and CBH were higher in the depositional plots than in the erosional plots, and those differences were enlarged with increasing slope gradients. Compared to the 5°-erosional plot, the activities of βX, βG and CBH respectively declined by 3.2–4.5%, 14.3–37.5% and 12.7–29.1% in the 10°-and 20°-erosional plots. The βX, βG and CBH activities were 2.2–18.1%, 17.3–32.1% and 14.8–86.2% higher in the 10°- and 20°-depositional plots than in the 5°-depositional plot. Moreover, the total soil CO 2 emissions from the whole erosion-deposition plots decreased as slopes steepened. The displaced runoff and sediment depleted soil moisture, SOC, clay and microbial biomass in the erosional plots but enhanced these resources in the depositional plots, which can account for the changes in C-acquiring enzyme activities. The spatial distribution of enzyme activities affected soil CO 2 emissions in a positive linear function. The sensitive responses of the C-acquiring enzyme activities and the controlling effects of C-acquiring enzyme activities on soil CO 2 emissions during erosion and deposition processes, should be properly considered in assessing the biological mechanism for nutrition cycling in regions predominated with fragmented eroding landscapes. [ABSTRACT FROM AUTHOR]