Dissolved organic carbon (DOC) derived from plant litter plays an important role in the ecosystem carbon balance and soil biogeochemistry. However, in boreal coniferous forests no integrated understanding exists of how understory vegetation contributes to litter leaching of DOC, nitrogen (N) and phosphorus (P) with different bioavailability at the forest stand level. We characterized water extractable leachates from fresh and decayed litter of dominant canopy and understory sources in a boreal coniferous forest, in order to explore the contribution of understory vegetation as a source of both total and bioavailable forms of DOC, N and P. Recently produced litter from deciduous species (including Vaccinium myrtillus ) yielded the highest amounts of DOC. However, this leaching potential decreased exponentially with mass loss through litter decay. The DOC lability generally showed little interspecific variation, although wood derived DOC was more recalcitrant. Lability decreased progressively with litter aging. Water extractable nutrients increased proportionally with DOC, and roughly a quarter (N) or half (P) had directly bioavailable inorganic forms. Scaled to annual litterfall at the forest stand, understory vegetation contributed ~ 80% of the water extractable DOC and nutrients from fresh litter, with > 60% coming from Vaccinium myrtillus alone. However, as litter decomposes, the data suggest a lower leaching potential is maintained with a larger contribution from needle, wood and moss litter. Our study shows that understory vegetation, especially V. myrtillus , is a key driver of litter DOC and nutrient leaching in boreal coniferous forests.

中文翻译：

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林下层在北方森林凋落物 DOC 和养分浸出中的作用

来自植物凋落物的溶解有机碳 (DOC) 在生态系统碳平衡和土壤生物地球化学中起着重要作用。然而，在北方针叶林中，对于林下植被如何导致 DOC、氮 (N) 和磷 (P) 在林分水平具有不同生物利用率的凋落物浸出没有综合理解。我们表征了来自北方针叶林中主要树冠和林下资源的新鲜和腐烂的枯枝落叶的可提取水浸出液，以探索林下植被作为 DOC、N 和 P 的总和生物可利用形式的来源的贡献。 最近产生的枯枝落叶来自落叶树种（包括 Vaccinium myrtillus ）的 DOC 含量最高。然而，随着凋落物腐烂导致的质量损失，这种浸出潜力呈指数下降。DOC 不稳定性通常显示很少的种间变异，尽管木材衍生的 DOC 更顽固。不稳定性随着垫料老化而逐渐降低。水可提取的营养素与 DOC 成比例增加，大约四分之一 (N) 或一半 (P) 具有直接生物可利用的无机形式。按林分的年度凋落物比例计算，林下植被贡献了约 80% 的可从新鲜凋落物中提取的水 DOC 和养分，其中超过 60% 仅来自牛痘。然而，随着枯枝落叶的分解，数据表明在针叶、木头和苔藓枯枝落叶的更大贡献下保持较低的浸出潜力。我们的研究表明，林下植被，尤其是桃金娘，是北方针叶林凋落物 DOC 和养分流失的关键驱动因素。