红树林是海洋蓝碳碳汇的重要生态系统，其碳库包括植被生物量和土壤碳库，后者主要来源是红树植物，而藻类、互花米草等也是潜在贡献者。中国红树林湿地碳循环与碳库虽然已有众多研究报道，但目前对不同红树林土壤碳库分布特征与来源还缺乏系统的比较研究，互花米草入侵和藻类异常增长对土壤碳库的贡献程度和影响机制还不清楚。本研究选择我国东南沿海有代表性的红树林区（福建云霄、广东高桥和福田、海南文昌和东寨港），通过对土壤的理化特性、碳含量、碳储量、碳同位素、碳溯源及红树林区藻类分布的比较研究，揭示了不同红树林区、不同红树群落和不同土壤深度的土壤有机碳（SOC）变化特征，量化了不同类型红树林湿地土壤碳库的主要来源，阐明了藻类异常增长和互花米草入侵对红树林土壤碳库的影响机制。主要结果和结论如下：（1）不同区域、不同红树群落、不同土壤深度SOC存在显著差异。四个红树林区SOC为云霄1.19±0.06%、高桥2.52±0.11%、东寨港0.81±0.10%、文昌4.78±0.35%，除东寨港外，SOC整体呈现随纬度而降低的趋势；海莲和银叶树的SOC相对较高，土壤表层的SOC显著高于深层。（2）土壤碳储量（Mg C/ha）亦存在地理和土壤深度的差异，变化趋势与SOC相似，文昌421.8±66.0、高桥260.3±28.0、云霄95.9±11.1、东寨港84.8±2.6。SOC和碳储量与土壤pH、盐度、容重、含水率间呈显著的相关关系。（3）土壤剖面δ13C值随深度的增加呈明显的增大趋势；δ13C平均值分别为云霄?25.37±0.52‰、高桥?26.68±0.38‰、东寨港?24.87±1.76‰和文昌?26.29±1.02‰，从北到南整体呈降低趋势。红树林区土壤碳来源主要是红树植物（61.56-79.92%），云霄和东寨港红树植物的碳贡献值较小（61.56±4.70%、65.88±16.82%），藻类贡献值较大（24.86±3.06%、24.38±12.17%），与互花米草入侵（云霄）和养殖业发达造成水体富营养化和藻类大量繁殖有关。（4）红树林区藻类以硅藻为主，福田红树林区藻类种类可能影响碳库的定量和溯源；云霄底栖微藻生物量、碳含量和碳贡献值比高桥高，与碳溯源结果耦合。这些结果为红树林湿地碳库的分布特征、形成过程与受控机制提供了新的认识，为中国红树林湿地资源保护和蓝碳碳汇管理提供科学依据。

Mangrove forest is an important type of coastal wetlands. Due to their high productivity and sedimentation rate, mangrove wetlands have very high marine carbon sink capacity, and are key ecosystems for blue carbon sink. Generally, mangrove wetland carbon stock includes vegetation and soil (sediment) carbon stocks. Besides mangrove source, algae and Spartina alterniflora could be other potential sources for mangrove soil carbon. Although many previous studies have assessed the stocks of soil organic carbon (SOC) of individual mangrove forest in China, no study has comprehensively investigated mangrove SOC and quantitatively estimated carbon sources. Moreover, it is still not clear about the controlling mechanisms for the effects of algal bloom and S. alterniflora invasion on mangrove soil carbon stocks. In this study, typical mangrove wetlands in the southeastern coasts of China (Yunxiao in Fujian Province, Gaoqiao and Futian in Guangdong Province, Dongzhaigang and Wenchang in Hainan Province) were selected for the investigation. Comparison were made on soil physicochemical properties, soil organic carbon densities, stable carbon isotopic values (δ13C), relative contributions of possible carbon sources to mangrove soil carbon, and diversity of algae communities, in order to explore the distribution patterns of SOC pools as influenced by latitudes, mangrove communities, and soil depths. The results from this study may provide new insights into the effect mechanisms of S. alterniflora invasion and algal bloom on mangrove soil carbon stocks. The main results and conclusions are listed below: (1)Mangrove SOC contents varied with sampling sites, mangrove communities, and depths of sediments. The SOC contents in the four sampling sites are 1.19±0.06%, 2.52±0.11%, 0.81±0.101% and 4.78±0.35% for Yunxiao, Gaoqiao, Dongzhaigang and Wenchang, respectively. Except Dongzhaigang, the values in the other three sites were generally decreasing with latitudes. The SOC contents in Bruguiera sexangula and Heritiera littoralis communities were relatively higher. The SOC contents of top soil fraction in the four sampling sites showed higher values than those of the deeper fractions. (2)Soil carbon stocks of the four mangrove sites varied with locations, and the variation trends were similar to that of SOC contents. The total carbon stock density in Wenchang (421.8±66.0 Mg C/ha) was higher than those in other three mangroves (260.3±28.0 Mg C/ha in Gaoqiao, 95.9±11.1 Mg C/ha in Yunxiao, and 84.8±2.6 Mg C/ha in Dongzhaigang). The regression analysis results revealed that soil pH, salinity, bulk density, and moisture were significantly correlated with the SOC contents in all four sites. (3)The δ13C values of soil profiles at different sites showed distinct increases with soil depths, and decrease tendency from north to south with the average values of –25.236±0.210‰ in Yunxiao, ?27.1±0.2‰ in Gaoqiao, ?26.1±0.3‰ in Dongzhaigang, and ?27.5±0.3‰ in Wenchang. The soil carbon sources analysis indicated that the major sources of SOC were all from mangrove plants (61.56-79.92%). In Yunxiao and Dongzhaigang, the contribution values from mangrove were lower (61.56% and 65.88%, respectively), while the algae contribution values were higher (24.86% and 24.38%, respectively), as compared to another two sites, which could be attributed to the biological invasion of S. alterniflora and algal bloom caused by water eutrophication due to the heavy aquaculture in these two mangrove wetlands. (4)Diatoms are dominant both in planktonic and benthic algae communities in mangrove areas. It is revealed that the high species diversity of algae communities might have effects on the quantity and source of carbon stock in mangrove nature reserve in Futian, Guangdong. The value of benthic microalgae biomass carbon content and carbon contribution to SOC in Yuanxiao was higher than that in Gaoqiao, which was coupled with the carbon contribution patterns of algae to soil organic carbon resulting from carbon sources analysis. Our results suggested that changes of microalgal species composition and biomass could influence the carbon content in the soil organic carbon in mangrove wetlands, especially at the surface level.The above results from this study provide new insights into distribution patterns, the formation process and controlling mechanisms of mangrove carbon stocks, which have significant implications for mangrove wetland conservation and blue carbon sink management in China.