Reviews and syntheses: Turning the challenges of partitioning ecosystem evaporation and transpiration into opportunities
Reviews and syntheses: Turning the challenges of partitioning ecosystem evaporation and transpiration into opportunities
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DOI：
10.5194/bg-16-3747-2019
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发表时间：
2019-03
期刊：
影响因子：
4.9
通讯作者：
P. Stoy;T. El-Madany;Joshua B. Fisher;P. Gentine;T. Gerken;Stephen P. Good;A. Klosterhalfen;
中科院分区：
文献类型：
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作者：
P. Stoy;T. El-Madany;Joshua B. Fisher;P. Gentine;T. Gerken;Stephen P. Good;A. Klosterhalfen;
抽象的。蒸发（E）和蒸腾（T）对气候、大气成分和土地利用的持续变化有不同的反应。很难将生态系统规模的蒸散量（ET）测量值划分为E和T，这使得验证卫星数据和陆面模型变得困难。在这里，我们回顾了目前在划分E和T方面的进展，并为如何改进理论和观测提供了一个展望。分析技术的最新进展为在生态系统尺度上划分E和T创造了新的机会，但其假设尚未得到充分验证。例如，许多划分E和T的方法依赖于植物冠层传导性和生态系统水分利用效率对大气蒸汽压亏缺（D）表现出最佳响应的概念。我们使用240涡度协方差通量塔的观测结果表明，最佳生态系统响应D是一个合理的假设，与最近的研究一致，但更多的分析是必要的，以确定该假设成立的条件。许多划分方法的另一个关键假设是，在理想的蒸腾条件下，ET可以近似为T，这已受到观测研究的挑战。我们证明，T可以超过95%的ET从某些生态系统，但其他生态系统似乎没有达到这个值，这表明，这一假设是生态系统依赖的分区的影响。重要的是要进一步改善方法划分E和T，但很少有多方法比较已进行日期。在气孔、叶片和冠层水平上对碳-水耦合的理解的进展为如何通过与光合作用的强耦合来量化T开辟了新的视角。光合作用可以在生态系统和全球范围内受到限制，新兴的数据来源包括太阳能诱导荧光，羰基硫通量测量，热成像等。这种比较将提高我们对生态系统水通量的机械理解，并提供必要的观测，以验证遥感算法和陆面模型，了解不断变化的全球水循环。
Abstract. Evaporation (E) and transpiration (T) respond differently to ongoing changes in climate, atmospheric composition, and land use. It is difficult to partition ecosystem-scale evapotranspiration (ET) measurements into E and T, which makes it difficult to validate satellite data and land surface models. Here, we review current progress in partitioning E and T and provide a prospectus for how to improve theory and observations going forward. Recent advancements in analytical techniques create new opportunities for partitioning E and T at the ecosystem scale, but their assumptions have yet to be fully tested. For example, many approaches to partition E and T rely on the notion that plant canopy conductance and ecosystem water use efficiency exhibit optimal responses to atmospheric vapor pressure deficit (D). We use observations from 240 eddy covariance flux towers to demonstrate that optimal ecosystem response to D is a reasonable assumption, in agreement with recent studies, but more analysis is necessary to determine the conditions for which this assumption holds. Another critical assumption for many partitioning approaches is that ET can be approximated as T during ideal transpiring conditions, which has been challenged by observational studies. We demonstrate that T can exceed 95 % of ET from certain ecosystems, but other ecosystems do not appear to reach this value, which suggests that this assumption is ecosystem-dependent with implications for partitioning. It is important to further improve approaches for partitioning E and T, yet few multi-method comparisons have been undertaken to date. Advances in our understanding of carbon–water coupling at the stomatal, leaf, and canopy level open new perspectives on how to quantify T via its strong coupling with photosynthesis. Photosynthesis can be constrained at the ecosystem and global scales with emerging data sources including solar-induced fluorescence, carbonyl sulfide flux measurements, thermography, and more. Such comparisons would improve our mechanistic understanding of ecosystem water fluxes and provide the observations necessary to validate remote sensing algorithms and land surface models to understand the changing global water cycle.