As part of a long-term study on the effects of nitrogen (N) loading in a shallow temperate lagoon, we measured rates of N₂ fixation associated with seagrass (Zostera marina) epiphytes during the summer from 2005 to 2019, at two sites along a gradient from where high N groundwater enters the system (denoted SH) to a more well-flushed outer harbor (OH). The data presented here are the first such long-term N₂ fixation estimates for any seagrass system and one of the very few reported for the phyllosphere in a temperate system. Mean daily N₂ fixation was estimated from light and dark measurements using the acetylene reduction assay intercalibrated using both incorporation of ¹⁵N₂ into biomass and a novel application of the N₂:Ar method. Surprisingly, despite a large inorganic N input from a N-contaminated groundwater plume, epiphytic N₂ fixation rates were moderately to very high for a seagrass system (OH site 14-year mean of 0.94 mmol N m⁻² d⁻¹), with the highest rates (2.6 mmol N m⁻² d⁻¹) measured at the more N-loaded eutrophic site (SH) where dissolved inorganic N was higher and soluble reactive phosphorus was lower than in the better-flushed OH. Over 95% of the total N₂ fixation measured was in the light, suggesting the importance of cyanobacteria in the epiphyte assemblages. We observed large inter-annual variation both within and across the two study sites (range from 0.1 to 2.6 mmol N fixed m⁻² d⁻¹), which we suggest is in part related to climatic variation. We estimate that input from phyllosphere N₂ fixation over the study period contributes on average an additional 20% to the total daily N load per area within the seagrass meadow.

作为对温带浅泻湖氮 (N) 负荷影响的长期研究的一部分，我们测量了2005 年至 2019 年夏季期间与海草 ( Zostera marina ) 附生植物相关的 N ₂固定速率，在沿线的两个地点从高氮地下水进入系统的地方（表示为 SH）到冲洗更良好的外港（OH）的梯度。这里提供的数据是对任何海草系统的首次此类长期 N ₂固定估计，也是为数不多的关于温带系统叶际圈的报道之一。平均每日 N ₂固定量是通过使用乙炔还原测定通过光和暗测量来估计的，并使用¹⁵ N _{2的掺入进行相互校准}转化为生物质以及 N ₂ :Ar 方法的新应用。令人惊讶的是，尽管来自受氮污染的地下水羽流输入了大量无机氮，但海草系统的附生 N _{2固定率中等至非常高（OH 站点 14 年平均值为 0.94 mmol N m} ⁻²  d ⁻¹），最高的比率（2.6 mmol N m ^-2  d ^-1）在氮负载较多的富营养化位点（SH）测得，其中溶解的无机氮较高，可溶性活性磷低于冲洗较好的OH。占总N _{2的95%以上}测量的固定是在光下进行的，这表明蓝细菌在附生植物群落中的重要性。我们观察到两个研究地点内部和之间存在较大的年际变化（范围从 0.1 至 2.6 mmol N 固定 m ^-2 d ^-1），我们认为这部分与气候变化有关。我们估计，研究期间叶际 N _{2固定的输入对海草草甸内每个区域的每日总氮负荷平均贡献了 20%。}