Salt marshes are large carbon reservoirs as part of blue carbon ecosystems. Unfortunately, there is limited information about the net ecosystem (NEE) and methane (CH₄) exchange between salt marshes and the atmosphere to fully understand their carbon dynamics. We tested the influence of biophysical drivers by plant phenological phases (i.e., Greenup, Maturity, Senescence and Dormancy) on NEE and CH₄ exchange in a grass-dominated temperate tidal salt marsh. We used three years of data derived from eddy covariance, PhenoCam (to measure vegetation phenology), and ancillary meteorological and water/soil variables. Overall, NEE showed significant differences among all phenological phases (p < 0.05), while CH₄ exchange had significant differences among all phases except for Greenup and Dormancy. Net CO₂ uptake was higher across Maturity (-61 g C-CO₂ m²), while CO₂ emissions were higher during Dormancy (182 g C-CO₂ m²). The lower but constant CO₂ emissions during Dormancy overshadowed the CO₂ uptake during the growing season and contributed to >72% of the annual CO₂ emissions in this ecosystem. Net CH₄ emissions were higher during Maturity (3.7 g C-CH₄ m²) and Senescence (4.2 g C-CH₄ m²). Photosynthetically active radiation (PAR) substantially influenced (r² > 0.57) daytime NEE across phenological phases, but a combination of variables including water table level (WTL), water temperature and atmospheric pressure were relevant to explain CH₄ exchange. The study site was an overall net carbon source to the atmosphere with annual emissions of 13-201 g C-CO₂ m⁻²yr⁻¹ and 8.5-15.2 g C-CH₄ m⁻²yr⁻¹. Our findings provide insights on: a) the role of plant phenological phases on ecosystem-scale CO₂ and CH₄ fluxes; b) challenges for modeling ecosystem-scale CO₂ and CH₄ fluxes in salt marshes; and c) the potential net loss of carbon to the atmosphere that should be considered for carbon management and accounting in these ecosystems.

盐沼是作为蓝碳生态系统一部分的大型碳库。不幸的是，关于盐沼与大气之间的净生态系统（NEE）和甲烷（CH ₄）交换的信息有限，无法充分了解其碳动态。我们测试了植物物候阶段（即Greenup，成熟度，衰老和休眠）对生物物理驱动力的影响，在草为主的温带潮汐盐沼中NEE和CH ₄交换。我们使用了三年的数据，这些数据来自涡度协方差，PhenoCam（用于测量植被物候）以及辅助气象和水/土壤变量。总体而言，NEE在所有物候期之间均表现出显着差异（p <0.05），而CH ₄除Greenup和Dormancy之外，所有阶段的交换都有显着差异。成熟期的净CO ₂吸收量更高（-61 g C-CO ₂ m ²），而休眠期间的CO ₂排放量更高（182 g C-CO ₂ m ²）。休眠期间较低但恒定的CO ₂排放量掩盖了生长季节的CO ₂吸收量，占该生态系统年CO ₂排放量的> 72％。在成熟期（3.7 g C-CH ₄ m ²）和衰老期（4.2 g C-CH ₄ m ²），CH _4的净排放量更高）。光合有效辐射（PAR）实质上影响了整个物候期的白天NEE （r ² > 0.57），但是包括地下水位（WTL），水温和大气压力在内的变量组合对于解释CH ₄交换至关重要。研究地点是大气的总体净碳源，年排放量为13-201 g C-CO ₂ m ^-2 yr ^-1和8.5-15.2 g C-CH ₄ m ^-2 yr ^-1。我们的发现为以下方面提供了见解：a）植物物候阶段对生态系统规模的CO ₂和CH ₄通量的作用；b）对生态系统规模的CO ₂建模的挑战盐沼中的CH ₄通量；c）这些生态系统中的碳管理和核算应考虑的潜在的碳向大气的净损失。