Ecological Stoichiometry and Carbon Storage Under Different Vegetation Types in Mountainous Area of Southern Ningxia, China

[Objective] To elucidate the differences in soil nutrient status and carbon sequestration capabilities among various vegetation types. [Methods] This study focused on six representative vegetation types in the southern mountainous areas of Ningxia: pure tree plantations (Prunus sibirica L. and Robinia pseudoacacia L.), mixed tree plantations (Robinia pseudoacacia L.+ Prunus sibirica L.), mixed tree and shrub plantations (Prunus davidiana (Carrière) Franch.+ Caragana korshinskii Kom.), shrub plantations (Hippophae rhamnoides L.), and grasslands. Through a combination of field surveys and laboratory analyses, we investigated the ecological stoichiometry and carbon storage of the 0—100 cm soil layer across these vegetation types. [Results] C, N, and P contents varied between 19.74～35.11 g/kg, 1.74～3.19 g/kg, and 1.60～1.69 g/kg, respectively, with both C and N contents decreasing with increasing soil depth. Furthermore, the C and N contents in the Robinia pseudoacacia L.+ Prunus sibirica L. were significantly higher than those in other types up to a depth of 80 cm, while P content showed no significant differences among types or soil layers. Soil C∶N ratio were significantly lower in Robinia pseudoacacia L.+ Prunus sibirica L. within the 0—40 cm layer, with no significant differences observed among vegetation types from 40—100 cm. Soil C∶P and N∶P ratios were significantly influenced by vegetation type, showing the highest values in the mixed forest of Robinia pseudoacacia L. and Prunus sibirica L.; Soil C∶N of these vegetation types showed no significant differences among layers. Soil C∶P and N∶P ratios were decreased with soil depth. Soil carbon storage 0—100 cm varied between 5.98～38.21 t/hm2 and had significant differences among these types, with all of them showed the order: Robinia pseudoacacia L.+ Prunus sibirica L.> Robinia pseudoacacia L.> Prunus sibirica L. > Hippophae rhamnoides L. > Prunus davidiana (Carrière) Franch.+ Caragana korshinskii Kom. > grassland. In addition, the mixed plantation of Robinia pseudoacacia L. and Prunus sibirica L. had significantly higher carbon storage than other vegetation types. [Conclusion] Tree and shrub lands in the southern Ningxia mountainous region have superior nutrient cycling patterns and carbon sequestration capabilities compared to grasslands, with the mixed planting model of Robinia pseudoacacia L. and Prunus sibirica L. being the most effective. Therefore, creating mixed plantations is an important approach to enhance soil carbon sequestration capacity.