Disentangling the effects of acidic air pollution, atmospheric CO 2 , and climate change on recent growth of red spruce trees in the Central Appalachian Mountains
Disentangling the effects of acidic air pollution, atmospheric CO 2 , and climate change on recent growth of red spruce trees in the Central Appalachian Mountains
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阐明酸性空气污染、大气CO 2 和气候变化对阿巴拉契亚山脉中部红云杉树近期生长的影响
DOI：
10.1111/gcb.14273
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发表时间：
2018
影响因子：
11.6
通讯作者：
Thomas, Richard B.
中科院分区：
文献类型：
--
作者：
Mathias, Justin M.;Thomas, Richard B.
在《清洁空气法》立法后的45年里，美国东部在减少酸性空气污染物方面取得了巨大进展，但更清洁的空气改善了森林健康的证据有限。本文研究了近期环境变化对红云杉(Picea ruensSarg.)生长和生理的影响。树木是森林健康的关键指示物种，横跨阿巴拉契亚山脉中部100公里样带的三个地点。我们结合了一个多指标方法，使用75年树木基础年轮生长年表、碳同位素识别(∆13C，树叶气体交换的替代物)和δ15N(生态系统N状况的替代物)来检查树木和生态系统水平对环境变化的响应。结果表明，这两个最重要的因素推动了自2010年以来树木生长的增加。1989年是酸性硫污染的减少和大气二氧化碳的增加，而氮氧化物污染物排放的减少和较温暖的春天发挥了较小但重要的作用。树轮∆13C签名自1989年以来显著增加，而树轮δ15N签名显著下降。这些同位素年代学提供了强有力的证据，表明C和N循环的同时变化，包括树木光合作用和气孔导度的增加以及生态系统N保留量的增加，与最近红云杉树生长的增加有关，并对生态系统从酸性污染中恢复具有重要意义。红云杉的内在水分利用效率(IWUE)在75年的年表中增加了~51%，这是由大气CO2和酸污染的变化驱动的，但iWUE与最近树木生长的增加无关。这项研究记录了从1989年开始，即美国酸性污染物开始下降约15年后，红云杉森林生态系统从普遍存在的酸性空气污染中恢复的复杂的环境相互作用。
In the 45 years after legislation of the Clean Air Act, there has been tremendous progress in reducing acidic air pollutants in the eastern United States, yet limited evidence exists that cleaner air has improved forest health. Here, we investigate the influence of recent environmental changes on the growth and physiology of red spruce (Picea rubensSarg.) trees, a key indicator species of forest health, spanning three locations along a 100 km transect in the Central Appalachian Mountains. We incorporated a multiproxy approach using 75‐year tree ring chronologies of basal tree growth, carbon isotope discrimination (∆13C, a proxy for leaf gas exchange), and δ15N (a proxy for ecosystem N status) to examine tree and ecosystem level responses to environmental change. Results reveal the two most important factors driving increased tree growth sinceca. 1989 are reductions in acidic sulfur pollution and increases in atmospheric CO2, while reductions in pollutant emissions of NOxand warmer springs played smaller, but significant roles. Tree ring ∆13C signatures increased significantly since 1989, concurrently with significant declines in tree ring δ15N signatures. These isotope chronologies provide strong evidence that simultaneous changes in C and N cycling, including greater photosynthesis and stomatal conductance of trees and increases in ecosystem N retention, were related to recent increases in red spruce tree growth and are consequential to ecosystem recovery from acidic pollution. Intrinsic water use efficiency (iWUE) of the red spruce trees increased by ~51% across the 75‐year chronology, and was driven by changes in atmospheric CO2and acid pollution, butiWUE was not linked to recent increases in tree growth. This study documents the complex environmental interactions that have contributed to the recovery of red spruce forest ecosystems from pervasive acidic air pollution beginning in 1989, about 15 years after acidic pollutants started to decline in the United States.