Center for Global Change and Ecological Forecasting, Shanghai Key Lab for Urban Ecological Processes and Eco-Restoration, School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China.
Atmospheric Sciences & Global Change, Pacific Northwest National Laboratory, Richland, Washington 99354, USA.
Plant Physiol. 2021 Apr 23;185(4):1682-1696. doi: 10.1093/plphys/kiab002.
Increasing sea levels associated with climate change threaten the survival of coastal forests, yet the mechanisms by which seawater exposure causes tree death remain poorly understood. Despite the potentially crucial role of nonstructural carbohydrate (NSC) reserves in tree survival, their dynamics in the process of death under seawater exposure are unknown. Here we monitored progressive tree mortality and associated NSC storage in Sitka-spruce (Picea sitchensis) trees dying under ecosystem-scale increases in seawater exposure in western Washington, USA. All trees exposed to seawater, because of monthly tidal intrusion, experienced declining crown foliage during the sampling period, and individuals with a lower percentage of live foliated crown (PLFC) died faster. Tree PLFC was strongly correlated with subsurface salinity and needle ion contents. Total NSC concentrations in trees declined remarkably with crown decline, and reached extremely low levels at tree death (2.4% and 1.6% in leaves and branches, respectively, and 0.4% in stems and roots). Starch in all tissues was almost completely consumed, while sugars remained at a homeostatic level in foliage. The decreasing NSC with closer proximity to death and near zero starch at death are evidences that carbon starvation occurred during Sitka-spruce mortality during seawater exposure. Our results highlight the importance of carbon storage as an indicator of tree mortality risks under seawater exposure.
与气候变化相关的海平面上升威胁着沿海森林的生存，但海水暴露导致树木死亡的机制仍知之甚少。尽管非结构性碳水化合物（NSC）储备在树木生存中可能起着至关重要的作用，但它们在海水暴露导致树木死亡过程中的动态变化尚不清楚。在这里，我们监测了美国华盛顿西部生态系统范围内海水暴露增加导致的西加云杉（Picea sitchensis）树木渐进性死亡和相关 NSC 储存。由于每月的潮汐入侵，所有暴露在海水中的树木在采样期间都经历了树冠叶片的减少，而具有较低活叶冠比例（PLFC）的个体死亡速度更快。树木的 PLFC 与地下盐分和针叶离子含量密切相关。随着树冠的减少，树木中的总 NSC 浓度显著下降，在树木死亡时达到极低水平（叶片和树枝中的浓度分别为 2.4%和 1.6%，茎和根中的浓度为 0.4%）。所有组织中的淀粉几乎完全消耗，而叶片中的糖仍保持在稳态水平。随着接近死亡，NSC 不断减少，而死亡时淀粉几乎为零，这表明在海水暴露导致西加云杉死亡期间发生了碳饥饿。我们的研究结果强调了碳储存作为海水暴露下树木死亡风险的一个重要指标。
