Understanding N budgets of tundra ecosystems is crucial for projecting future changes in plant community composition, greenhouse gas balances and soil N stocks. Winter warming can lead to higher tundra winter nitrogen (N) mineralization rates, while summer warming may increase both growing season N mineralization and plant N demand. The undulating tundra landscape is inter-connected through water and solute movement on top of and within near-surface soil, but the importance of lateral N fluxes for tundra N budgets is not well known. We studied the size of lateral N fluxes and the fate of lateral N input in the snowmelt period with a shallow thaw layer, and in the late growing season with a deeper thaw layer. We used ¹⁵N to trace inorganic lateral N movement in a Low-arctic mesic tundra heath slope in West Greenland and to quantify the fate of N in the receiving area. We found that half of the early-season lateral N input was retained by the receiving ecosystem, whereas half was transported downslope. Plants appear as poor utilizers of early-season N, indicating that higher winter N mineralization may influence plant growth and carbon (C) sequestration less than expected. Still, evergreen plants were better at utilizing early-season N, highlighting how changes in N availability may impact plant community composition. In contrast, later growing season lateral N input was deeper and offered an advantage to deeper-rooted deciduous plants. The measurements suggest that N input driven by future warming at the study site will have no significant impact on the overall N₂O emissions. Our work underlines how tundra ecosystem N allocation, C budgets and plant community composition vary in their response to lateral N inputs, which may help us understand future responses in a warmer Arctic.

了解苔原生态系统的氮预算对于预测植物群落组成、温室气体平衡和土壤氮储量的未来变化至关重要。冬季变暖会导致苔原冬季氮 (N) 矿化率升高，而夏季变暖可能会增加生长季节的氮矿化和植物对氮的需求。起伏的苔原景观通过近地表土壤顶部和内部的水和溶质运动相互联系，但横向 N 通量对苔原 N 收支的重要性尚不清楚。我们研究了融雪层较浅的融雪期和生长季后期融雪层较深的侧向 N 通量的大小和侧向 N 输入的归宿。我们用了¹⁵N 在西格陵兰的低北极中部苔原荒地斜坡中追踪无机横向 N 运动，并量化接收区中 N 的归宿。我们发现，接收生态系统保留了一半的早季横向 N 输入，而另一半则被输送到下坡。植物似乎是早期 N 的不良利用者，表明较高的冬季 N 矿化可能对植物生长和碳 (C) 封存的影响低于预期。尽管如此，常绿植物更善于利用​​早季氮，突出了氮可用性的变化如何影响植物群落组成。相比之下，生长后期的横向氮输入更深，为根深蒂固的落叶植物提供了优势。测量结果表明，研究地点未来变暖驱动的 N 输入不会对整体 N 产生显着影响。₂ O 排放。我们的工作强调了苔原生态系统氮分配、碳预算和植物群落组成在对横向氮输入的响应方面如何变化，这可能有助于我们了解未来在温暖的北极地区的响应。