Abstract:Soil organic carbon (SOC) is the largest carbon pool in terrestrial ecosystems and plays a key role in preventing soil degradation, conserving soil health and coping with global climate change. Soil minerals are important components of the soil solid phase, and their interactions with soil organic carbon can directly affect soil interfacial activity, physicochemical properties and fertility. The mineral carbon pump (MnCP) concept emphasizes the key role of soil minerals in driving the active organic carbon sequestration, and describes the functional orientation of minerals in the process of soil organic carbon stabilization. In this paper, we systematically reviewed the concept of MnCP with the main line of mineral-mediated soil carbon sequestration, introduced the five mechanisms underlying MnCP-mediated carbon sequestration, the regulatory factors, and the development of related characterization techniques, and finally proposed the key scientific questions to be further investigated under the framework of MnCP.

Abstract:【Objective】 Mineral-associated organic carbon (MAOC) is the most important of soil organic carbon(SOC), and its mineralization characteristics have an important impact on soil carbon sequestration and global climate change. As an important topographic factor, slope position significantly affects the interaction and stability of organic carbon and soil minerals. However, the influence of slope positions on mineralization characteristics of MAOC in soils is not fully understood. 【Method】 In this study, typical citrus orchard soils at different slope positions were sampled, and the aggregates with sizes of >2, 2～0.25, 0.25～0.053, and <0.053 mm were obtained by physical fractionation. Moreover, the MAOC in aggregates were separated to investigate the mineralization characteristics of MAOC at varying slope positions (upper slope, middle slope, and lower slope) through indoor cultivation. The influence of soil physicochemical factors and hydrophobicity on MAOC mineralization was analyzed by Infrared spectroscopy (FTIR), Redundancy analysis (RDA), and Hierarchical partitioning analysis. 【Result】 The results showed that the cumulative mineralization (Ct), mineralization rate and potential mineralization (Co) of MAOC in citrus orchard soil at lower slopes were significantly higher than those at upper and middle slopes, but the ratio of Co/MAOC at lower slope was significantly lower compared with upper and middle slopes. With the decrease in aggregate size, the Ct, mineralization rate, and Co of MAOC in citrus orchard soil at each slope position showed an upward trend, while the mineralization intensity of MAOC gradually weakened. RDA results showed that the Co was significantly positively correlated with pH, SOC, MAOC, TN, and C/N (P<0.05), and significantly negatively correlated with iron and aluminum oxides (Fed/Ald, Feo/Alo, and Fep/Alp) and hydrophobicity (P<0.05). Co/MAOC was significantly positively correlated with iron and aluminum oxides and hydrophobicity, but significantly negatively correlated with Co, Ct, pH, SOC, MAOC, TN, and C/N. Hierarchical partitioning analysis revealed that Alo, Alp, and Fep emerged as significant factors influencing the mineralization of MAOC. Variation decomposition analysis showed that the combined effects of Alo, Alp, Fep, C/N, MAOC, and Feo significantly affected MAOC mineralization in aggregates with different particle sizes at different slope positions. 【Conclusion】 The slope positions have obvious effects on the mineralization characteristics of MAOC in aggregates in citrus orchard soils. The findings of this study are of great significance for understanding the formation mechanisms and stability of mineral-bound organic carbon in soil aggregates and in enhancing soil organic carbon sequestration in citrus orchards at different slope positions in hilly regions of southern China.