Rapid increases in shrubland and forest intrinsic water-use efficiency during an ongoing megadrought
Rapid increases in shrubland and forest intrinsic water-use efficiency during an ongoing megadrought
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DOI：
10.1073/pnas.2118052118
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发表时间：
2021-12-28
影响因子：
11.1
通讯作者：
Ehleringer, James R.
中科院分区：
文献类型：
--
作者：
Kannenberg, Steven A.;Driscoll, Avery W.;Ehleringer, James R.
在全球范围内，随着大气二氧化碳浓度的增加，内在用水效率（iWUE）在过去一个世纪中急剧上升。长期干旱事件可能会进一步加速这种增长，例如美国西南部持续数十年的“特大干旱”。然而，该地区 iWUE 的直接测量很少，并且很大程度上仅限于树木，这可能会使 iWUE 趋势的估计偏向于更加湿润、高海拔地区，并忽略其他关键植物功能类型（例如在该地区大部分地区占主导地位的灌木）的响应。在这里，我们发现证据表明，由于最近的干燥趋势，西南地区的 iWUE 正在以有记录的最快速率之一增加。三种常见灌木物种的增加幅度尤其大，它们对干旱的 iWUE 敏感性高于美国西部常见树种黄松。灌木和树木 iWUE 对大气干旱变化的敏感性超过了对大气 [CO2] 增加的敏感性。在其他条件相同的情况下，向节水型植被的转变将对植物健康产生积极的影响。然而，整个西南地区植物密度降低、生长减弱和植被死亡率增加的持续趋势表明，iWUE 的增加不太可能抵消干旱化的负面影响。
Globally, intrinsic water-use efficiency (iWUE) has risen dramatically over the past century in concert with increases in atmospheric CO2 concentration. This increase could be further accelerated by long-term drought events, such as the ongoing multidecadal "megadrought" in the American Southwest. However, direct measurements of iWUE in this region are rare and largely constrained to trees, which may bias estimates of iWUE trends toward more mesic, high elevation areas and neglect the responses of other key plant functional types such as shrubs that are dominant across much of the region. Here, we found evidence that iWUE is increasing in the Southwest at one of the fastest rates documented due to the recent drying trend. These increases were particularly large across three common shrub species, which had a greater iWUE sensitivity to aridity than Pinus ponderosa, a common tree species in the western United States. The sensitivity of both shrub and tree iWUE to variability in atmospheric aridity exceeded their sensitivity to increasing atmospheric [CO2]. The shift to more water-efficient vegetation would be, all else being equal, a net positive for plant health. However, ongoing trends toward lower plant density, diminished growth, and increasing vegetation mortality across the Southwest indicate that this increase in iWUE is unlikely to offset the negative impacts of aridification.