Morgan Bryn E, Araki Ryoko, Trugman Anna T, Caylor Kelly K
Department of Geography, University of California, Santa Barbara, Santa Barbara, CA, USA.
Earth Research Institute, University of California, Santa Barbara, Santa Barbara, CA, USA.
Nat Ecol Evol. 2025 Jul 29. doi: 10.1038/s41559-025-02810-8.
Vegetation responses to soil moisture limitation play a key role in land-atmosphere interactions and are a major source of uncertainty in future projections of the global water and carbon cycles. Vegetation water-use strategies-that is, how plants regulate transpiration rates as the soil dries-are highly dynamic across space and time, presenting a major challenge to inferring ecosystem responses to water limitation. Here we show that, when aggregated globally, water-use strategies derived from point-based soil moisture observations exhibit emergent patterns across and within climates and vegetation types along a spectrum of aggressive to conservative responses to water limitation. Water use becomes more conservative, declining more rapidly as the soil dries, as mean annual precipitation increases and as woody cover increases from grasslands to savannahs to forests. We embed this empirical synthesis within an ecohydrological framework to show that key ecological (leaf area) and hydroclimatic (aridity) factors driving demand for water explain up to 77% of the variance in water-use strategies within ecosystem types. All biomes respond to ecological and hydroclimatic demand by shifting towards more aggressive water-use strategies. However, woodlands reach a threshold beyond which water use becomes increasingly conservative, probably reflecting the greater hydraulic risk and cost of tissue damage associated with sustaining high transpiration rates under water limitation for trees than grasses. These findings highlight the importance of characterizing the dynamic nature of vegetation water-use strategies to improve predictions of ecosystem responses to climate change.
植被对土壤水分限制的响应在陆地-大气相互作用中起着关键作用，并且是全球水和碳循环未来预测中不确定性的主要来源。植被的水分利用策略，即植物在土壤变干时如何调节蒸腾速率，在空间和时间上具有高度动态性，这对推断生态系统对水分限制的响应构成了重大挑战。在这里，我们表明，当在全球范围内汇总时，从基于点的土壤湿度观测中得出的水分利用策略在不同气候和植被类型之间以及内部呈现出从对水分限制的激进响应到保守响应的一系列新兴模式。随着年平均降水量的增加以及从草原到稀树草原再到森林的木质覆盖度增加，水分利用变得更加保守，随着土壤变干，水分利用下降得更快。我们将这一实证综合纳入一个生态水文框架，以表明驱动水分需求的关键生态（叶面积）和水文气候（干旱度）因素可解释生态系统类型内水分利用策略中高达77%的方差。所有生物群落都通过转向更激进的水分利用策略来响应生态和水文气候需求。然而，林地达到了一个阈值，超过该阈值后水分利用变得越来越保守，这可能反映了在水分限制下维持树木高蒸腾速率比草本植物与更大的水力风险和组织损伤成本相关。这些发现突出了表征植被水分利用策略动态性质对于改善生态系统对气候变化响应预测的重要性。
