Asymmetric response of Amazon forest water and energy fluxes to wet and dry hydrological extremes reveals onset of a local drought‐induced tipping point
Asymmetric response of Amazon forest water and energy fluxes to wet and dry hydrological extremes reveals onset of a local drought‐induced tipping point
复制标题
DOI：
10.1111/gcb.16933
复制
发表时间：
2023-09
影响因子：
11.6
通讯作者：
N. Restrepo-Coupe;Bradley O'Donnell Christoffersen;Marcos Longo;Luciana F. Alves;K. S. Campos;Alessandro C da Araujo;R. D. de Oliveira;N. Prohaska;R. da Silva;Raphael Tapajós;K. Wiedemann;S. Wofsy;S. Saleska
中科院分区：
文献类型：
--
作者：
N. Restrepo-Coupe;Bradley O'Donnell Christoffersen;Marcos Longo;Luciana F. Alves;K. S. Campos;Alessandro C da Araujo;R. D. de Oliveira;N. Prohaska;R. da Silva;Raphael Tapajós;K. Wiedemann;S. Wofsy;S. Saleska
了解亚马逊流域加剧的水文循环--表现为日益频繁的洪水和干旱--对热带森林的水和能量循环的影响，对于应对预测生态系统对气候变化的反应，包括森林“引爆点”的挑战至关重要。在这里，我们利用对塔帕约州S国家森林12年多来(2001年至2020年)来自涡旋协方差的水和能量通量的观测，以及来自生物测量的相关生态动态，研究了水文极端对森林功能的影响。测量范围包括2015-2016年严重的厄尔尼诺干旱和2008-2009年的拉尼娜潮湿事件。我们发现，森林对厄尔尼诺-南方涛动(ENSO)的响应非常强烈：干旱减少了可用于蒸发蒸腾的水(ET)，导致感热通量(H)大幅增加。通过假定蒸腾作用(T)与光合作用成正比的方法来分配ET，我们发现水分胁迫导致的冠层电导(Gs)的降低导致了T的下降，部分地被更高的蒸发量(E)所补偿。反之，异常湿润的拉尼娜期间T偏高，E偏低，而季节ET变化不大。两次厄尔尼诺-南方涛动(ENSO)事件都导致了森林结构的变化，表现为雨季叶面积指数降低。然而，仅在2015-2016年厄尔尼诺期间，我们观察到由于植被功能减慢(通过气孔关闭和大量落叶)，蒸腾通量的强大气象控制(通过能量可获得性和大气需求)崩溃。干旱减少的T和Gs，较高的H和E，被较高的温度和水汽压差的反馈放大，表明森林功能已经超过了一个临界点，从这个临界点开始缓慢恢复，但在干旱之后，恢复得很慢。在地方尺度上确定这种临界点(超过这个临界点以后可能会发生不可逆转的过程)，对于预测流域规模的森林能量和水循环变化至关重要，这会导致森林功能放缓，可能导致亚马逊森林转变为交替退化的状态。
Understanding the effects of intensification of Amazon basin hydrological cycling—manifest as increasingly frequent floods and droughts—on water and energy cycles of tropical forests is essential to meeting the challenge of predicting ecosystem responses to climate change, including forest “tipping points”. Here, we investigated the impacts of hydrological extremes on forest function using 12+ years of observations (between 2001–2020) of water and energy fluxes from eddy covariance, along with associated ecological dynamics from biometry, at the Tapajós National Forest. Measurements encompass the strong 2015–2016 El Niño drought and La Niña 2008–2009 wet events. We found that the forest responded strongly to El Niño‐Southern Oscillation (ENSO): Drought reduced water availability for evapotranspiration (ET) leading to large increases in sensible heat fluxes (H). Partitioning ET by an approach that assumes transpiration (T) is proportional to photosynthesis, we found that water stress‐induced reductions in canopy conductance (Gs) drove T declines partly compensated by higher evaporation (E). By contrast, the abnormally wet La Niña period gave higher T and lower E, with little change in seasonal ET. Both El Niño‐Southern Oscillation (ENSO) events resulted in changes in forest structure, manifested as lower wet‐season leaf area index. However, only during El Niño 2015–2016, we observed a breakdown in the strong meteorological control of transpiration fluxes (via energy availability and atmospheric demand) because of slowing vegetation functions (via shutdown of Gs and significant leaf shedding). Drought‐reduced T and Gs, higher H and E, amplified by feedbacks with higher temperatures and vapor pressure deficits, signaled that forest function had crossed a threshold, from which it recovered slowly, with delay, post‐drought. Identifying such tipping point onsets (beyond which future irreversible processes may occur) at local scale is crucial for predicting basin‐scale threshold‐crossing changes in forest energy and water cycling, leading to slow‐down in forest function, potentially resulting in Amazon forests shifting into alternate degraded states.