【Objective】 Continuous advancements have been achieved in optimizing the formulation, application strategies, and overall applicability of seaweed-derived fertilizers. However, a mechanistic understanding of how their key functional components modulate soil processes remains incomplete. This study investigated the impact of brown algae substances, central functional constituents of seaweed fertilizers, on soil properties, carbon fractions, carbon turnover-related enzymes, and associated greenhouse gas emissions. 【Method】 In this study, a soil incubation experiment was conducted with five treatments: control (CK), brown seaweed powder treatment(Sea), sodium alginate treatment with a viscosity of 66 mPa·s (Alg66), sodium alginate treatment with a viscosity of 360 mPa·s(Alg360), and fucoidan treatment (Fuc). The soil was incubated at 25 ℃ for 112 days and sampled periodically to determine the soil properties, carbon composition, enzyme activity, and greenhouse gas emissions. On the 56th and 112th day of incubation, the effects of adding different brown algae substances on soil β-glucosidase(BG), cellobiohydrolase(CBH), β-xylosidase (BX), and N-acetyl-β-glucosaminidase (NAG) and particulate organic carbon (POC), mineral-associated organic carbon (MOC), dissolved organic carbon (DOC), and easily oxidizable organic carbon (EOC) were determined. Nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄)emissions were monitored during the first 50 days of incubation. 【Result】 The results showed that the addition of different brown algae substances had varying effects on the soil properties. Compared to CK, the addition of brown seaweed substances significantly increased soil organic carbon and total nitrogen content. The most significant effects on organic carbon and total nitrogen were Fuc treatment and Sea treatment, respectively. The Sea treatment enhanced soil available phosphorus and potassium content by 19.83% and 260.23%, respectively. Conversely, the brown algae polysaccharide treatments (Alg66, Alg360, Fuc) decreased soil available phosphorus by 17.67%, 2.74%, and 20.15% and soil available potassium by 11.41%, 3.85%, and 6.36%, respectively. Also, the Fuc treatment significantly improved the activated carbon component content, particularly the dissolved organic carbon, which was significantly different from other treatments at the end of the incubation period, and 6.34 times that of CK. The Fuc treatment also increased the enzyme activities of soil BG, CBH, BX, and NAG. Compared to the CK, the addition of brown algal substances increased CO₂ emissions, while the addition of Alg66 and Alg360 reduced N₂O emissions. There was no significant difference in the effect of all treatments on CH₄ emission. Therefore, new fertilizers that combine soil improvement and greenhouse gas reduction functions can be developed by optimizing the component ratios of brown algae substances. 【Conclusion】 Brown algae substances can enhance soil carbon and nitrogen nutrients, whereas fucoidan can significantly enhance soil enzyme activity and active carbon components and sodium alginate can reduce N₂O emissions. These results show that brown algae substances have a certain potential for green enhancement, with different components exerting varying effects on soil properties, thus, showing potential for the development of brown algae substances for the production of new fertilizers.