Abstract Understanding the mechanisms and controlling factors of ecosystem CO2 exchange in tidal wetlands is of great benefit for research concerning the global carbon cycle and climate change. In spite of this, the multiple controls of ecosystem-atmosphere CO2 exchange in coastal wetlands subject to subdaily tidal flooding have yet to be adequately addressed. In this study, we investigated the tidal influence on ecosystem CO2 exchange in a Phragmites salt marsh of an intertidal shoal in the Changjiang estuary, based on eddy covariance (EC) measurements. The results revealed that the study area acted as a strong sink for atmospheric CO2 (net ecosystem exchange, NEE = -901 g C m−2) in 2018. Photosynthetically active radiation (PAR), air temperature (Ta), and vapor pressure deficit (VPD) were major drivers of NEE on both diel and multi-day scales. The tides, along with the bio-meteorological variables, strongly affect ecosystem photosynthesis (gross primary production, GPP) and ecosystem respiration (Reco) in the tidal wetland, especially on the multi-day scale. Regardless of which flux partitioning method was utilized, tidal inundation generally imposed inhibitory effects on GPP, which were directly attributed to tidal water level (TWL) and salinity. The daytime data-based estimates of Reco was also suppressed on average under the tidal inundation condition when Ta was higher relative to the non-inundation condition, reflecting the influence of TWL on Reco and the reduced sensitivity of Reco to Ta. We observed that NEE responded positively or negatively to tidal flooding, depending on the magnitude of tidal suppression on GPP and Reco. When Ta was roughly between 28 and 32°C and PAR was > 1200 μmol m−2 s−1, GPP was suppressed by tides more than Reco during the early and rapid vegetative stage, while during the peak vegetative stage, the opposite was true. This study not only shows the unique impact of tidal salt marsh wetlands on carbon uptake, but it also represents an example of a coastal wetland in which tidal inundation promotes the net uptake of CO2.

中文翻译：

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潮间带芦苇盐沼中潮汐对生态系统CO2交换的影响

摘要 了解潮汐湿地生态系统CO2交换的机制和控制因素，对于全球碳循环和气候变化的研究具有重要意义。尽管如此，受潮汐洪水影响的沿海湿地生态系统-大气 CO2 交换的多重控制尚未得到充分解决。在这项研究中，我们基于涡度协方差 (EC) 测量，研究了潮汐对长江口潮间带浅滩芦苇盐沼中生态系统 CO2 交换的影响。结果表明，研究区在 2018 年充当了大气 CO2（净生态系统交换，NEE = -901 g C m−2）的强汇。 光合有效辐射（PAR）、气温（Ta）和蒸汽压差(VPD) 是日间和多日尺度上 NEE 的主要驱动因素。潮汐与生物气象变量一起，强烈影响潮汐湿地的生态系统光合作用（总初级生产，GPP）和生态系统呼吸（Reco），尤其是在多日尺度上。无论使用哪种通量分配方法，潮汐淹没通常都会对 GPP 产生抑制作用，这直接归因于潮汐水位 (TWL) 和盐度。在潮汐淹没条件下，当 Ta 相对于非淹没条件更高时，基于白天数据的 Reco 估计值也被平均抑制，这反映了 TWL 对 Reco 的影响以及 Reco 对 Ta 的敏感性降低。我们观察到 NEE 对潮汐洪水的反应是正面还是负面，这取决于 GPP 和 Reco 上潮汐抑制的程度。当Ta大致在28-32°C之间，PAR>1200 μmol m-2 s-1时，GPP在早期和快速营养阶段受到潮汐的抑制大于Reco，而在营养高峰期则相反. 这项研究不仅显示了潮汐盐沼湿地对碳吸收的独特影响，而且还代表了潮汐淹没促进二氧化碳净吸收的沿海湿地的一个例子。