Characteristics of Soil Organic Carbon Distribution and Influencing Factors in Typical Artificial Forests with Coastal Saline-alkalinene Soils

This study was conducted to investigate the characteristics of soil organic carbon distribution and its key influencing factors in artificial forests with coastal saline-alkaline soil, thereby providing a scientific basis for improving the carbon sink capacity of these ecosystems. Five typical 15-year-old coastal saline-alkaline artificial forests comprising poplar (Populus tomentosa), white wax (Fraxinus chinensis), elm (Ulmus pumila), zelkova (Zelkova serrata), or soap pod (Gleditsia sinensis) trees established concurrently in Jiangsu were selected as study sites. Comprehensive analyses were conducted by measuring physical and chemical properties, enzyme activities, and carbon contents in three soil layers (0-20, >20-40, and >40-60 cm). Various methods, including structural equation modeling, were used, which revealed the following: (1) Improvements in soil physical properties did not differ substantially among forest types; with increasing soil depth, coastal saline-alkaline forest soil bulk density, pH, electrical conductivity, and alkalization increased, whereas aeration and porosity decreased. (2) Compared with other forest soils, zelkova and soap pod forest soils had a lower pH, electrical conductivity, and alkalinity; the superior amelioration of their saline-alkaline soils was in contrast to the limited improvements in the soils of poplar and fast-growing white wax forests. (3) Soil sucrase activities were highest in the poplar forest, whereas soil β-glucosidase and urease activities were highest in the elm forest and lowest in the soap pod forest. (4) The organic carbon content of the surface soil layer (0-20 cm) did not differ significantly among forest stands (P>0.05); however, organic carbon contents of soil layers below 20 cm differed significantly among forest stands (P<0.05), with the elm forest soil sequestering the most carbon. (5) Soil acidity and urease activity were the main determinants of the carbon storage capacity of coastal saline-alkaline soil. Therefore, soil carbon sequestration in artificial forests with coastal saline-alkaline soil may be enhanced by improving soil structural characteristics and promoting the activity of soil enzymes, including urease, to increase the organic carbon content of deep soil layers.