Effects of different fertilization on soil organic carbon distribution and storage in micro-aggregates of red paddy topsoil Effects of external nitrogen additions on soil organic carbon dynamics and the mechanism Soil organic carbon sequestration rate and its influencing factors in farmlands of semi-arid regions—A case study in Zhuanglang County, Gansu Province Changes in land use and land cover and soil organic carbon storage in the densely populated village landscapes of China′s Yangtze Plain from the 1940 to 2002 Soil Carbon Sequestration and Its Relationship with Soil pH in Qinglangang Mangrove Wetlands in Hainan Island