当地地下水减少加剧了旱地河岸林地对气候干旱的反应,Global Change Biology

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当地地下水减少加剧了旱地河岸林地对气候干旱的反应
Global Change Biology ( IF 10.8 ) Pub Date : 2022-08-10 , DOI: 10.1111/gcb.16376
Jared Williams _{1,

2} , John C Stella _{1,

3} , Steven L Voelker ₄ , Adam M Lambert _{2,

5} , Lissa M Pelletier ₁ , John E Drake ₃ , Jonathan M Friedman ₆ , Dar A Roberts _{7,

8} , Michael Bliss Singer _{8,

9,

10}

Affiliation

Graduate Program in Environmental Science, College of Environmental Science and Forestry, State University of New York, Syracuse, New York, USA.
Marine Science Institute, University of California, Santa Barbara, California, USA.
Department of Sustainable Resources Management, State University of New York College of Environmental Science and Forestry, Syracuse, New York, USA.
College of Forest Resources and Environmental Science, Michigan Technological University, Houghton, Michigan, USA.
Cheadle Center for Biodiversity and Ecological Restoration, University of California, Santa Barbara, California, USA.
U.S. Geological Survey, Fort Collins Science Center, Fort Collins, Colorado, USA.
Department of Geography, University of California, Santa Barbara, California, USA.
Earth Research Institute, University of California, Santa Barbara, California, USA.
School of Earth and Environmental Sciences, Cardiff University, Cardiff, UK.
Water Research Institute, Cardiff University, Cardiff, UK.

旱地河岸林地被认为可以通过浅而稳定的地下水位在当地缓冲干旱。然而，气候变化导致更频繁和更严重的干旱事件，伴随着温度升高，蒸发需求增加和地下水供应减少共同威胁着这些依赖地下水的生态系统的持续存在。我们对径向生长和季节性（半年度）碳同位素鉴别（Δ ¹³C) 调查 2012 年至 2019 年加州南部最大的自由流动河流沿岸河岸棉白杨对史无前例的加州干旱的反应。我们的目标是确定旱地河岸林地干旱压力的主要驱动因素和指标，确定它们对水文气候压力因素的耐受阈值，并最终评估它们对气候变化的脆弱性。河岸树木对沿河的干旱条件高度敏感，在干旱高峰期表现出生长受抑制和强烈的气孔关闭（根据减少的 Δ ^{13 C 推断）。}然而，径向生长模式和 Δ ¹³C 在气候条件和地下水下降率不同的地点之间变化很大。我们表明，与气候因素相反，地下水下降率是干旱胁迫地点差异的主要驱动因素，并且在地下水下降更快的地点，树木对温度表现出更大的敏感性。在各个地点，个别树木的径向生长与 Δ ^{13 C 之间的相关性较高，以及树木之间 Δ}¹³ C 的较高相互相关性表明干旱胁迫更大。^{树木在 0.5 m year −1}时表现出对地下水下降的耐受阈值超出此范围，干旱压力变得越来越明显和严重。对于超过此阈值的地点，当总地下水退缩超过 ~3 m 时，会出现生理压力峰值。这些发现表明，与更极端的干旱相关的干旱引起的地下水减少是对旱地河岸林地的主要威胁，并增加了它们对预计温度升高的敏感性。

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Local groundwater decline exacerbates response of dryland riparian woodlands to climatic drought

Dryland riparian woodlands are considered to be locally buffered from droughts by shallow and stable groundwater levels. However, climate change is causing more frequent and severe drought events, accompanied by warmer temperatures, collectively threatening the persistence of these groundwater dependent ecosystems through a combination of increasing evaporative demand and decreasing groundwater supply. We conducted a dendro-isotopic analysis of radial growth and seasonal (semi-annual) carbon isotope discrimination (Δ¹³C) to investigate the response of riparian cottonwood stands to the unprecedented California-wide drought from 2012 to 2019, along the largest remaining free-flowing river in Southern California. Our goals were to identify principal drivers and indicators of drought stress for dryland riparian woodlands, determine their thresholds of tolerance to hydroclimatic stressors, and ultimately assess their vulnerability to climate change. Riparian trees were highly responsive to drought conditions along the river, exhibiting suppressed growth and strong stomatal closure (inferred from reduced Δ¹³C) during peak drought years. However, patterns of radial growth and Δ¹³C were quite variable among sites that differed in climatic conditions and rate of groundwater decline. We show that the rate of groundwater decline, as opposed to climate factors, was the primary driver of site differences in drought stress, and trees showed greater sensitivity to temperature at sites subjected to faster groundwater decline. Across sites, higher correlation between radial growth and Δ¹³C for individual trees, and higher inter-correlation of Δ¹³C among trees were indicative of greater drought stress. Trees showed a threshold of tolerance to groundwater decline at 0.5 m year⁻¹ beyond which drought stress became increasingly evident and severe. For sites that exceeded this threshold, peak physiological stress occurred when total groundwater recession exceeded ~3 m. These findings indicate that drought-induced groundwater decline associated with more extreme droughts is a primary threat to dryland riparian woodlands and increases their susceptibility to projected warmer temperatures.

更新日期：2022-08-10

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