Abstract: Through the analyses of soil organic carbon content and vegetation inp ut, this paper studied the difference in soil organic carbon accumulation capabi lity of two typical tidal wetlands, one (A) was on the erosion bank with Phragmites communis and sandy loam soil at southeast Dongtan in Shanghai, and the other (B) was on the alluvial bank with P. communis, Spartina alterniflora, and c lay soil at northeast Dongtan of Chongming Island. The main formation causes of the difference were analyzed based on the determinations of soil microbial activ ities and physical-chemical properties. In A, the average soil total organic ca rbon content was 4610% (P<005) of that in B, while the annual abovegro und vegetation dry mass was only 916% lower than that in B, illustrating that the soil organic carbon output was higher in A than in B. The total count of soi l bacteria and the activities of soil catalase and invertase in A were 3.82 time s (P<005), 4681% (P<005), and 3433% (P<005) higher than th ose in B, respectively, and the soil microbial respiration in A was also higher than that in B, which indicated that the stronger soil microbial C- metabolic a ctivity in A was the main cause inducing the lower soil organic carbon accumulat ion capability. The sandy loam soil in A had higher porosity and lower salinity and moisture, being favorable to the growth of soil microbes and the decompositi on of soil organic carbon, while the clay soil in B had higher salinity and mois ture but lower microbial activity, leading to the weaker soil organic carbon dec omposition and higher organic carbon accumulation.

Key words: mountainous area of southern Ningxia, typical plant, rhizosphere soil, soil carbon, soil nitrogen.