Soil Carbon Cannot Efficiently Accumulate in Sand‐Based River Valley

ABSTRACT River valley is traditionally thought a landform with efficient soil carbon accumulation, because it is generally a low‐lying wetter area relative to surrounding landforms. However, soil carbon has been less studied in sand‐based river valley of arid and semi‐arid regions. This study was to mainly understand the capacity of soil carbon accumulation in sand‐based Xilin River valley in arid and semi‐arid Mongolia Plateau by comparing with the surrounding steppe and sandland. We found that soil carbon storage per unit area sequenced in steppe > meadow > sandland, which was inversely associated with soil sand fraction. Soil carbon storage in river valley meadow was close to the mean value in three landforms, without significant difference between both. River valley wetland and water body were also synthesized at weak soil carbon accumulation. These results can be concluded that soil carbon accumulation in the low‐lying Xilin River valley had no predominance relative to the surrounding high‐lying landforms. Sand‐based soils are more aerated than loamy and clayey soils, and their organic carbon is more easily decomposed. Again, sand‐based soils are mainly composed of silicate; their low quantities of organic and inorganic carbons are further mineralized and dissolved by water erosion in the river valley, respectively. Furthermore, low plant productivity, arid and semi‐arid climate, weak sediment transport, and deposition cannot efficiently promote soil carbon accumulation. We suggest that river valley cannot be overestimated in evaluating the storage of soil carbon in arid and semi‐arid regions.