珠江口红树林土壤甲烷和二氧化碳通量特征及其影响因素研究

The Regular Pattern and Influencing Factors of CO_(2) and CH_(4) Fluxes from Mangrove Soil

红树林作为碳密度最高的森林生态系统之一,在碳生物地球化学循环过程中发挥着重要作用。该研究以广州市珠江河口红树林土壤为主要研究对象,于2020年8月—2021年7月运用静态箱法分别对红树林中的外滩(靠近海岸)、中滩(植被聚集)和内滩(靠近内陆)的土壤-大气界面的CO_(2)和CH_(4)通量进行观测,探讨红树林生态系统CO_(2)和CH_(4)排放通量的时空分布特征及其对环境因子(温度、含水量以及土壤理化性质)的响应。此外,基于稳定碳同位素(δ^(13)C)特征和Keeling Plot方法综合评估红树林生态系统CO_(2)和CH_(4)通量的来源特征。结果表明,研究期间平均CH_(4)通量为18.97μmol·m^(-2)·h^(−1),CO_(2)通量均值为4.19 mmol·m^(-2)·h^(−1)。CO_(2)和CH_(4)的通量均具有显著的时空差异性,CO_(2)通量最高值出现在3月,CH_(4)在9月达到最高值。CO_(2)通量排序为内滩>中滩>外滩,CH_(4)通量则表现为中滩>外滩>内滩。土壤含水量、pH、EC、ORP和有机碳含量与CO_(2)通量呈负相关关系,CH_(4)通量与土壤含水量、pH和有机碳含量呈正相关关系。虽然研究区红树为C3植物,然而土壤呼吸产生的CO_(2)的同位素特征在内滩为−16.05‰,中滩为−17.73‰,外滩为−29.77‰,内滩和中滩表现为C4植物特征,由此表明藻类成为土壤呼吸来源。内滩的有机质分解程度最高。研究区CH_(4)的分馏系数在外滩、中滩和内滩均小于1.055,CH_(4)产生方式以乙酸产甲烷为主。该研究系统探讨了红树林生态系统CO_(2)和CH_(4)通量、来源及其影响因素,对进一步了解红树林对碳循环及其气候变化的影响具有重要意义。

Mangrove,one of the most carbon intensive forest ecosystems,plays an important role in the carbon biogeochemical cycle.The study area located in the Pearl River Estuary.Filed campaign was conducted each month from August 2020 to July 2021.The closed chamber method was used to determine the emission fluxes of CO_(2)and CH_(4) from the mangrove soil in the seaward(close to the ocean),middle(vegetation cover)and landward(close to the land)beaches to analyze the spatial and temporal distribution characteristics of CO_(2)and CH_(4) emission fluxes and their influencing factors.In addition,the source apportionment of CO_(2)and CH_(4) was evaluated based on the stable carbon isotope(δ^(13)C)and Keeling Plot method.The results showed that the mean CH_(4) and CO_(2) fluxes during the study period were 18.97μmol·m^(-2)·h^(−1)and 4.19 mmol·m^(-2)·h^(−1),respectively.Both CO_(2)and CH_(4) fluxes showed significant temporal and spatial variations.The maximum value of CO_(2) and CH_(4) fluxes was observed in March and September,respectively.The CO_(2)fluxes were ranked as landward>middle>seaward,and CH_(4) fluxes were ranked as middle>seaward>landward.Soil moisture,pH,EC,ORP and OC(soil organic carbon content)had negative effects on CO_(2) fluxes,while CH_(4)fluxes were positively correlated with soil moisture,pH,and OC.Although mangroves in the study area were C3 plants,theδ^(13)C of CO_(2)produced by soil respiration was−16.05‰in the landward,−17.73‰in the middle,and−29.77‰in the seaward forest.The landward and middle forests have characteristics of C4 plants,indicating that algae became the source of soil respiration.Fractionation factors ofδ^(13)C-CH_(4)in the seaward,middle and landward forests were less than 1.055,suggesting that acetate fermentation served as a key methanogenic pathway of CH_(4)emission.This study systematically discussed the fluxes,sources,and influencing factors of CO_(2)and CH_(4)in mangroves.It is of great significance to further understand the impact of mangroves on the carbon cycle and climate change.