全球变暖是人类生存和发展面临的共同挑战，中国“力争2060年前实现碳中和”，其基本实现途径为“减排”和“增汇”。海岸带蓝碳，介于海洋“蓝碳”和陆地“绿碳”之间，是指红树林、盐沼湿地和海草床等海岸植被生态系统的固定碳，其单位面积固碳能力是陆地生态系统的10倍以上。红树林通过固定大气中的二氧化碳（CO₂）实现碳汇功能，同时是排放甲烷（CH₄）的弱源，可能一定程度上抵消其碳汇。受海岸带红树林地域难以抵达、潮汐和台风等极端天气影响，当前尚缺少长时间序列CO₂和CH₄通量同步监测数据及评估体系。由于全球变暖、海平面上升和其他人为活动（比如森林砍伐和鱼虾养殖）等因素影响，红树林面积逐年减少，成为最受威胁的蓝碳生态系统类型之一，定量分析海岸带红树林恢复区CO₂与CH₄综合增温潜势与抵消程度，从机理上探讨影响红树林碳汇功能的主控因子，将为完善海岸带蓝碳估算体系提供重要理论支撑，为践行国家“碳中和”战略中发挥重要作用。

本文以浙南蓝碳生态过程监测试验站红树林恢复区为研究对象，2017-2020年利用涡度相关技术监测秋茄红树林（Kandelia candel）CO₂通量和2020年CH₄通量，定量评估红树林恢复区CO₂和CH₄通量日变化、季节变化与年际变化，比较干季与湿季气体通量变化的主要影响因素，探究红树林恢复区CH₄排放源对CO₂碳汇的抵消程度。本文得到的主要结果如下：

（1）2017-2020年海岸带红树林恢复区整体表现为CO₂的“碳汇”（负值表示碳汇），CO₂净生态系统碳交换量（Net Ecosystem Exchange of CO₂，NEE）日变化模式呈现出“U”形曲线，在中午12：30达到极值，为-9.08 μmol m^-2 s^-1。湿季（3-9月）NEE日变化模式与干季基本相同，日变化曲线幅度在湿季大于干季（10-2月），湿季固碳能力大于干季。植被总初级生产力（Gross Primary Production, GPP）与生态系统呼吸（Ecosystem Respiration，Reco）月变化趋势都呈单峰状态，月平均NEE呈现“W”型趋势。红树林恢复区在春季（3-5月）及秋季（9-10月）碳汇较强，在夏季（6-8月）和冬季（12-2月）出现碳汇功能减弱现象。2018年3-5月温度高于其他年份同期，导致红树林恢复区植被总初级生产力较高，碳汇功能较强。红树林生态系统CO₂年际变化存在显著差异，监测数据较为完整的2017和2020年NEE分别为-362和-490 gC m^-2，随着林龄增加，人工移植林红树林碳汇功能逐渐增加，但低于自然树龄较高红树林。

（2）红树林恢复区为CH₄排放源（正值表示排放源），CH₄通量日变化趋势显示，上午9:00-10:00出现波谷，下午14:00出现波峰，日平均排放范围为0.0069 到 0.064 μmol m^-2 s^-1。CH₄在湿季较高，干季较低，呈单峰分布，8月达到排放峰值，日平均排放趋势与气温基本一致。2020年红树林恢复区CH₄排放量约为11 gC m^-2。100年尺度上CO₂和CH₄的持续全球增温潜势（Sustained Global Warming Potential，SGWP）分别为-1801 gCO₂ m^-2和683.7 gCO₂-eq m^-2，净平衡为-1117.3 gCO₂-eq m^-2。红树林在100年时间尺度上由CO₂碳汇引起的负辐射强迫主导，CH₄排放引起的“变暖效应”抵消了CO₂碳吸收的“降温效应”约38%，该比例高于自然红树林。相对于自然红树林，红树林恢复区CH₄排放对应的SGWP抵消程度相对较高，因此估算红树林碳汇功能时CH₄排放不可忽略。

（3）红树林恢复区气温、降雨量、光合有效辐射、饱和水汽压差、潮汐水位高度等环境因子表现出明显的季节性，湿季值均高于干季。基于相互作用分析环境因子与NEE在不同时间尺度（小时、日、多日）相对重要性，结果显示，三个时间尺度上，光合有效辐射（Photosynthetically Active Radiation，PAR）、潜热（Latent Heat，LE）和显热（Sensible Heat，H）通量是主控因子；在每日和多天尺度上，除PAR、LE、H外，气温（Air Temperature，Tair）和饱和水汽压差（Vapor Pressure Deficit，VPD）是主要控制因子；潮汐水位高度（Tidal Water evel，TWL）在多天尺度与NEE显示出较为明显的相互作用。

（4）多种环境因子共同影响着红树林的光合作用和呼吸作用，日间NEE对PAR的光响应及夜间NEE对Tair的响应在不同环境条件下具有差异。结果显示，日间NEE随PAR增大而降低，夜间NEE随Tair增大呈指数型增加。在干季低温和湿季高温时，光合作用受到了抑制，日间NEE较大。植被光利用效率（Light Use Efficiency，LUE）在中等气温时最高，随着VPD的增大呈指数下降。潮汐通过直接和间接作用影响NEE，在大潮期时，日间NEE及夜间NEE都小于小潮期，主要归因于潮汐淹没的直接作用，形成了缺氧环境及对气体扩散的阻碍。通过路径分析发现，潮汐可以通过增加Tair间接作用对NEE产生正效应。海风通过调节Tair产生对NEE产生间接负效应，缓解午后光合作用高温高VPD的压力，减小日间NEE。

Global warming is a common challenge to human survival and social development. China proposes to "strive to achieve carbon neutrality by 2060". The basic way to achieve this goal is to "reduce emissions" and "increase sinks" of carbon. Coastal zone blue carbon, a type of carbon type between oceanic "blue carbon" and terrestrial "green carbon", refers to the fixed carbon of coastal vegetation ecosystems such as mangroves, salt marsh, and seagrass beds, whose carbon sequestration capacity per unit area is 10 times more than that of terrestrial ecosystems. Mangroves achieve their carbon sink function by fixing carbon dioxide (CO₂) in the atmosphere, while being a weak source of methane (CH₄) emissions, which may offset their carbon sink potential to some extent. Due to the geographical inaccessibility of mangroves in coastal zones, tides and extreme weather conditions such as typhoons, there is a lack of long time series of field monitoring data and assessment systems. Due to global warming, sea level rise and other anthropogenic activities (e.g. deforestation and fish and shrimp farming), mangrove area is decreasing year by year as one of the most threatened wetland types, and the CO₂ and CH₄ emission fluxes and influencing factors in the coastal zone mangrove restoration area deserve in-depth study. The quantitative analysis of CO₂ and CH₄ combined global warming potential (GWP) and the CH₄ offsetting degree in the mangrove restoration area of coastal zonewill help to improve the estimation of blue carbon in coastal zone. It is urgent to study to the mechanism between the carbon sink of mangroves and the main controlling factors. This study will provide important theoretical support for improving the blue carbon estimation system in the coastal zone and play an important role in the implementation of the national "carbon neutral" strategy. The mangrove restoration area located at the Blue Carbon Ecological Process Monitoring Experiment Station in southern Zhejiang Province to monitor CO₂ fluxes and CH₄ fluxes in mangrove forests (Kandelia candel) from 2017 to 2020 using the eddy covariance technique. We quantitatively assessed the daily, seasonal, and interannual variability of CO₂ and CH₄ fluxes in the mangrove restoration area. The main factors influencing the changes of carbon fluxes in dry (from March to September) and wet (from October to Feberary of next year) seasons were compared, and the extent of offsetting CO₂ carbon sinks by CH₄ emission sources in mangrove restoration areas was explored. The main results obtained in this paper are as follows.

（1）From 2017 to 2020, the coastal zone mangrove restoration area acted as a "carbon sink" of CO₂ (negative values indicate carbon sink). The daily variation patterns of Net Ecosystem Exchange of CO₂ (NEE) showed a "U" shaped curve. The extreme value of -9.08 μmol m^-2 s^-1 was reached at 12:30 p.m. The daily variation pattern of NEE in the wet season (March-September) was basically the same as that in the dry season, and the amplitude of the daily variation curve was greater in the wet season than in the dry season (October-February), and the carbon sequestration capacity in the wet season was greater than that in the dry season. The monthly trends of Gross Primary Production (GPP) and Ecosystem Respiration (Reco) were both single-peaked, and the monthly average NEE showed a "W" pattern. The mangrove restoration area showed strong carbon sinks in spring (March-May) and autumn (September-October), and weakened carbon sinks in summer (June-August) and winter (December-February). The temperature from March to May in 2018 was higher than other months of the same year, resulting in higher GPP of vegetation and stronger carbon sink function in the mangrove restoration area. There were significant interannual variations in carbon fluxes in mangrove ecosystems, and the NEEs in 2017 and 2020, where monitoring data were more complete, were -362 and -490 gC m^-2, respectively, and the carbon sink function of mangroves in planted transplantation forests gradually increased with increasing forest age, but was lower than that of natural mature mangroves.

（2）The mangrove restoration area is a source of CH₄ emissions (positive values indicate sources of emissions), and the daily variations of CH₄ fluxes shows a trough from 9:00 a.m. to 10:00 a.m. and a peak at 14:00 p.m. The daily average emissions range from 0.0069 to 0.064 μmol m^-2 s^-1. CH₄ fluxes are higher in the wet season and lower in the dry season, with a single-peaked annual variation and peak emissions in August, and the trend of daily average emissions is generally consistent with the daily average temperature. CH₄ emissions from the mangrove restoration area in 2020 are about 11 g C m^-2. The SGWP for CO₂ and CH₄ on a 100-year scale is -1801 gCO₂ m^-2 and 683.7 gCO₂-eq m^-2, with a net balance of -1117.3 gCO₂-eq m^-2, indicating a net cooling effect on climate over centurial timescales, CH₄-induced warming effect can offset 38% of the CO₂-induced cooling effect at a 100-year time horizon using the metric of sustained-flux global warming potentials. Compared with natural mangroves, the degree of SGWP offset of CH₄ emissions in mangrove restoration areas is relatively high.

（3）Environmental factors such as temperature, rainfall, photosynthetic effective radiation, vapor pressure deficit, and tidal water level  in the mangrove restoration area showed obvious seasonality, with higher values in the wet season than in the dry season. Based on the interaction analysis of the relative importance of environmental factors and NEE at different time scales (hourly, daily, and multi-day), the results show that photosynthetic effective radiation, latent heat and sensible heat flux are the main controlling factors at three time scales; at daily and multi-day scales, air temperature and saturated water vapor pressure deficit are the main controlling factors, except PAR, LE, and H. Tidal water level height shows a more obvious interaction with NEE at the multi-day scale.

（4）A variety of environmental factors combined to influence photosynthesis and respiration in mangroves, and the photoresponse of daytime NEE to PAR and nighttime NEE to Tair differed under different environmental conditions. The results showed that daytime NEE decreased with increasing PAR and nighttime NEE increased exponentially with increasing Tair. Photosynthesis was suppressed at low temperatures in the dry season and high temperatures in the wet season, and daytime NEE was greater. Vegetation light use efficiency was highest at moderate temperatures and decreased exponentially with increasing VPD. Tides affect NEE through direct and indirect effects, with daytime NEE and nighttime NEE during spring tides being smaller than those during neap tides, which is attributed to the direct effect of tidal inundation. Path analysis showed that tides can positively affect NEE through the indirect effect of increasing Tair. Sea breeze has an indirect negative effect on NEE by regulating Tair, relieving the pressure of high temperature and high VPD for photosynthesis in the afternoon and reducing daytime NEE.