Have improvements in ozone air quality reduced ozone uptake into plants?
Have improvements in ozone air quality reduced ozone uptake into plants?
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DOI：
10.1525/elementa.399
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发表时间：
2020
影响因子：
4.4
通讯作者：
A. C. Ronan;J. Ducker;J. Schnell;C. Holmes
中科院分区：
文献类型：
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作者：
A. C. Ronan;J. Ducker;J. Schnell;C. Holmes
臭氧（O3）的峰值水平——通过浓度指标（如超过40 ppb阈值的O3累积暴露量（AOT40）和s型加权累积暴露量（W126））进行量化——在过去几十年里，美国和欧洲大部分地区的臭氧（O3）峰值水平有所下降。过去的研究表明，AOT40和W126的改善表明植物损伤的减少，尽管人们普遍认为是叶片中的O3通量，而不是环境中的O3浓度，是植物损伤的原因。利用涡流相关通量塔获得的植物吸收臭氧的新数据集，我们测试了AOT40、W126或夏季平均臭氧是否是叶片累积吸收臭氧的趋势的有用指标，这是植物毒性臭氧剂量（POD或PODy，其中y是解毒阈值）。在美国和欧洲的32个站点中，我们发现大多数站点的AOT40和W126浓度指标在2005-2014年间分别下降了25个和28个。然而，POD0在大多数位点（18个）增加。多项统计检验表明，aot40、W126和平均臭氧浓度指标均不能很好地预测po0的时间趋势或变异（R2≤0.15）。这些结果对使用解毒阈值（POD3）不敏感。O3浓度与植物吸收量的差异趋势是由于气孔对通量的控制，这种控制受环境变异性和植物因子的影响。因此，2005年至2014年期间，在我们所评估的地点，POD没有得到广泛、明显的改善。因此，浓度指标的降低对臭氧对植被影响的方向和程度给出了过于乐观和不完整的描述。由于O3通量与浓度之间缺乏相关性，在评估O3对植物的伤害时，通量指标应优于浓度指标。
Peak levels of ozone (O3)—quantified by concentration metrics such as accumulated O3 exposure over a threshold of 40 ppb (AOT40) and the sigmoidal-weighted cumulative exposure (W126)—have decreased over large parts of the United States and Europe in the last several decades. Past studies have suggested that these improvements in AOT40 and W126 indicate reductions in plant injury, even though it is widely recognized that O3 flux into leaves, not ambient O3 concentration, is the cause of plant damage. Using a new dataset of O3 uptake into plants derived from eddy covariance flux towers, we test whether AOT40, W126, or summer mean O3 are useful indicators of trends in the cumulative uptake of O3 into leaves, which is the phytotoxic O3 dose (POD or PODy, where y is a detoxification threshold). At 32 sites in the United States and Europe, we find that the AOT40 and W126 concentration metrics decreased over 2005–2014 at most sites: 25 and 28 sites, respectively. POD0, however, increased at a majority (18) of the sites. Multiple statistical tests demonstrate that none of the concentration metrics—AOT40, W126, and mean O3—are good predictors of POD0 temporal trends or variability (R2 ≤ 0.15). These results are insensitive to using a detoxification threshold (POD3). The divergent trends for O3 concentration and plant uptake are due to stomatal control of flux, which is shaped by environmental variability and plant factors. As a result, there has been no widespread, clear improvement in POD over 2005–2014 at the sites we can assess. Decreases in concentration metrics, therefore, give an overly optimistic and incomplete picture of the direction and magnitude of O3 impacts on vegetation. Because of this lack of relation between O3 flux and concentration, flux metrics should be preferred over concentration metrics in assessments of plant injury from O3.