High N Storage but Low N Recovery After Long-Term N-Fertilization in a Subtropical Cunninghamia lanceolata Plantation Ecosystem: A 14-Year Case Study.
High N Storage but Low N Recovery After Long-Term N-Fertilization in a Subtropical Cunninghamia lanceolata Plantation Ecosystem: A 14-Year Case Study.
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DOI：
10.3389/fpls.2022.914176
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发表时间：
2022
影响因子：
5.6
通讯作者：
中科院分区：
文献类型：
--
作者：
森林是所有陆地生态系统最重要的氮库之一。近几十年来，大气氮沉降的增加引起了人们对施氮对森林氮循环影响的兴趣的增加。然而，对森林生态系统氮储存量的准确评估仍然难以实现。我们对杉木 [Cunninghamia lanceolata (Lamb.) Hook] 人工林进行了 14 年的试验，探讨长期施氮肥对氮储存和回收率的影响。我们的研究样地位于一块连续施肥超过 14 年（2004 年至 2017 年）的田地中，尿素施肥量为 0（N0，对照）、60（N60，低氮）、120（N120，中氮）和 240（N240，高氮）kg N hm−2a−1。收集的数据包括林下、凋落物和各种植物器官（即叶、枝、茎、根和树皮）中的氮含量和生物量，以及不同深度的土壤氮含量和密度。结果表明，施氮地块的生态系统总氮储量是对照地块的1.1-1.4倍。生态系统总氮的约 12.36% 储存在植被（植物器官、凋落物和林下）中，87.64% 储存在土壤（0-60cm）中。植物器官、凋落物和土壤的氮储存量高于林下层。与对照相比，中氮（1.2 倍）和高氮（1.4 倍）处理中的植物氮吸收量显着更高。施氮处理林下层氮素回收率为负值，低于对照。该林长期施用氮肥导致氮素回收率低（平均11.39%），氮素流失量高（平均91.86%），表明杉木人工林生态系统氮素利用效率较低。我们的研究结果进一步阐明了重要陆地生态系统中氮的分布，并提高了我们对区域氮循环的理解。
Forests are among the most important N pools of all terrestrial ecosystems. Elevated atmospheric N deposition in recent decades has led to increased interest in the influences of N application on forest N cycles. However, accurate assessments of N storage in forest ecosystems remain elusive. We used a 14-year experiment of a Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] plantation to explore how long-term N fertilization affected N storage and recovery rates. Our study plots were located in a field that had been continuously fertilized over 14 years (2004–2017) with urea at rates of 0 (N0, control), 60 (N60, low-N), 120 (N120, medium-N), and 240 (N240, high-N) kg N hm−2a−1. Data were collected that included N content and biomass in the understory, litter, and various plant organs (i.e., leaves, branches, stems, roots, and bark), as well as soil N content and density at different depths. Results showed that the total ecosystem N storage in the N-fertilized plots was 1.1–1.4 times higher than that in the control plots. About 12.36% of the total ecosystem N was stored in vegetation (plant organs, litter, and understory) and 87.64% was stored in soil (0–60 cm). Plant organs, litter, and soil had higher N storage than the understory layer. Significantly higher plant N uptake was found in the medium-N (1.2 times) and high-N (1.4 times) treatments relative to the control. The N recovery rate of the understory layer in the N-fertilized treatments was negative and less than that in the control. Application of long-term N fertilizer to this stand led to a low N recovery rate (average 11.39%) and high loss of N (average 91.86%), which indicate low N use efficiency in the Chinese fir plantation ecosystem. Our findings further clarify the distribution of N in an important terrestrial ecosystem and improve our understanding of regional N cycles.
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