Abstract Wetlands store large carbon (C) stocks and play important roles in biogeochemical C cycling. However, the effects of environmental and anthropogenic pressures on C dynamics in lower coastal plain forested wetlands in the southern U.S. are not well understood. We established four eddy flux stations in two post-harvest and newly-planted loblolly pine plantations (YP2–6, 2–6 yrs old; YP2–8, 2–8 yrs old), a rotation-aged loblolly pine plantations (MP, 15–27 yrs old), and a mixed bottomland hardwood forest (BHF, >100 yrs old) in the lower coastal plain of North Carolina, USA. We analyzed the gross primary productivity (GPP), ecosystem respiration (RE) and net ecosystem exchange (NEE) for age-related trends, interannual variability in response to climate forcing, and management-related disturbances from 2005 – 2017. For the first few years after being harvested, pine plantations were net C sources (NEE = 1133 and 897 g C m–2 yr–1 in YP2–6 and YP2–8, respectively). The MP was a strong C sink (–369 to –1131 g C m–2 yr–1) over the entire study period. In contrast, BHF was a C source (NEE = 87 g C m–2 yr–1 to 759 g C m–2 yr–1) in most years, although in the first year it did show a net C uptake (NEE = –368 g C m–2 yr–1). The source activity of BHF may have been related to increasing overstory tree mortality and diameter growth suppression. Decreases in relative extractable water in pine plantations enhanced GPP and RE. Pine plantations regained status as C sinks 5–8 years after harvest and recovered C equivalent to post-harvest losses at 8–14 years. Thus, coastal pine plantations have a net C uptake for only about half the 25-year rotation period, suggesting that they have decreased climate mitigation potential in comparison to protecting primary forests. However, primary forests in this area may be vulnerable to ecosystem transition, and subsequent C loss, due to the changing environmental conditions at the land-ocean interface.

中文翻译：

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美国东南部管理和天然沿海森林湿地的长期碳通量和平衡

摘要 湿地储存大量的碳（C）储量并在生物地球化学 C 循环中发挥重要作用。然而，环境和人为压力对美国南部沿海平原森林湿地 C 动态的影响尚不清楚。我们在两个收获后和新种植的火炬松人工林（YP2-6，2-6 岁；YP2-8，2-8 岁），一个轮龄火炬松人工林（MP， 15-27 岁），以及美国北卡罗来纳州低海岸平原的混合低地阔叶林（BHF，> 100 岁）。我们分析了 2005 年至 2017 年的总初级生产力 (GPP)、生态系统呼吸 (RE) 和净生态系统交换 (NEE)，以了解与年龄相关的趋势、响应气候强迫的年际变化以及与管理相关的干扰。在收获后的最初几年，松树种植园是净碳源（在 YP2-6 和 YP2-8 中，NEE 分别为 1133 和 897 g C m-2 yr-1）。在整个研究期间，MP 是强 C 汇（–369 至 –1131 g C m–2 yr–1）。相比之下，BHF 在大多数年份都是碳源（NEE = 87 g C m-2 yr-1 到 759 g C m-2 yr-1），尽管在第一年它确实显示了净碳吸收（NEE = –368 g C m–2 yr–1)。BHF 的源活动可能与增加的上层乔木死亡率和直径增长抑制有关。松林中相对可提取水的减少提高了 GPP 和 RE。松树种植园恢复状态，因为 C 在收获后 5-8 年下沉，并在 8-14 年恢复相当于收获后损失的 C。因此，沿海松树种植园在 25 年轮作周期的大约一半内净吸收碳，表明与保护原始森林相比，它们降低了减缓气候变化的潜力。然而，由于陆海界面环境条件的变化，该地区的原始森林可能容易受到生态系统转变和随后的碳损失的影响。