Linking tree water status to the carbon budget: identifying mechanisms of drought-induced tree mortality in Pinus nigra and Picea abies

森林生态系统培育了大部分陆地生物多样性，是维持生命的元素(如碳、氮)循环的主要推动力。然而，越来越频繁地发生越来越强烈的高温和干旱事件已导致全球范围内广泛的森林死亡。预计未来干旱事件的增加可能会进一步威胁森林的生存，从而危及森林提供的维持生命的服务的持续流动。令人惊讶的是，人们对干旱如何杀死树木的基本理解存在很大差距。目前的工作假说(碳饥饿、碳转移受阻、水力/共生失效)都缺乏实验支持，但对这些机制的透彻理解对于预测对森林生态系统、未来植被分布和元素循环的影响至关重要。在这里，我提出了一系列明确设计的实验，以区分干旱导致树木死亡的不同机制。实验设计将涵盖所研究树木的形态、生理和功能方面，并将包括对大气成分的操纵。这些实验的结果将提高我们对干旱诱导的树木死亡的理解，并将有助于制定适应和缓解策略。因此，在一个更温暖、更干燥、二氧化碳含量更高的世界里，它们对于保护森林生态系统至关重要。

Forest ecosystems foster the bulk of terrestrial biodiversity and are a major driving force of the cycling of life-supporting elements (e.g., carbon, nitrogen). However increasingly frequent occurrences of increasingly intense heat and drought events have led to widespread forest mortality around the globe. Anticipated future increases of drought events may further threaten the survival of forests and hence jeopardize the sustained flow of the life-supporting services they provide. Surprisingly, there are large gaps in the fundamental understanding of how drought kills trees. Current working hypotheses (carbon starvation, impeded carbon translocation, hydraulic/symplastic failure) all lack experimental support but a thorough understanding of these mechanisms is central to predicting impacts on forest ecosystems, future vegetation distribution and element cycling. Here I propose a series of experiments explicitly designed to partition the different mechanisms of drought-induced tree mortality. The experimental design will cover morphological, physiological and functional aspects of the studied trees and will include manipulations of the atmospheric composition. The results of these experiments will improve our understanding of drought-induced tree mortality and will be helpful for developing adaptation and mitigation strategies. Thus they are essential for the conservation of forest ecosystems in a warmer and dryer, CO2-enriched world.