Stephens C, Medlyn B, Williams L, Knauer J, Inbar A, Pendall E, Arndt S K, Beringer J, Ewenz C M, Hinko-Najera N, Hutley L B, Isaac P, Liddell M, Meyer W, Moore C E, Cranko Page J, Silberstein R, Woodgate W
Hawkesbury Institute for the Environment, Western Sydney University, Richmond, New South Wales, Australia.
School of Agriculture, Food and Ecosystem Sciences, The University of Melbourne, Parkville, Victoria, Australia.
Glob Chang Biol. 2025 Jul;31(7):e70361. doi: 10.1111/gcb.70361.
Climate change-driven increases in drought risk pose a critical threat to global carbon and water cycles. However, ecosystem-scale responses remain poorly quantified, particularly for severe, multiyear drought events. We addressed this gap by examining ecosystem-scale carbon and water flux sensitivity to the extreme 2018-19 drought in Australia using data from 14 eddy covariance flux sites. The ecosystems span grasslands and semi-arid woodlands to tropical and temperate forests. The driest sites (classed as "grass" and "very dry") experienced drastic productivity impacts, with a 65% decrease in Gross Primary Productivity (GPP) over 2 years relative to the pre-drought average. However, fluxes in "dry," "seasonally wet" and "wet" ecosystems showed remarkable resistance, with no overall change in GPP. All sites recovered rapidly; carbon fluxes in the first post-drought year matched (and generally exceeded) those of a climatically similar pre-drought year. Drought responses were strongly mediated by ecosystem-specific strategies. The driest ecosystems showed direct coupling of productivity to water availability, while intermediate ecosystems (dry and seasonally wet) leveraged stored soil water to maintain evapotranspiration and productivity under drought. At these sites, water was conserved over wet periods (evapotranspiration < demand, despite sufficient rainfall) and consumed over dry periods (evapotranspiration > rainfall). This mechanism mitigating periodic water stress under high rainfall variability likely contributed to the notable drought resistance of the dry and seasonally wet sites. The monthly water deficit index (MWDI) emerged as a robust predictor of productivity across space, highlighting that short-term water availability deficits strongly influence overall ecosystem composition. Analysis of drought response mechanisms suggested rapid leaf loss under water stress, particularly at the driest sites. Our findings underscore the importance of accounting for sub-surface water storage and diverse drought response strategies in vegetation models. We provide critical benchmarks for improving parameterization of plant-water relations, aiding efforts to inform climate-robust management strategies.
气候变化导致干旱风险增加，对全球碳循环和水循环构成了重大威胁。然而，生态系统尺度的响应仍未得到充分量化，尤其是对于严重的多年干旱事件。我们通过利用来自14个涡度协方差通量站点的数据，研究了澳大利亚2018 - 19年极端干旱期间生态系统尺度的碳通量和水通量敏感性，从而填补了这一空白。这些生态系统涵盖了草原、半干旱林地、热带和温带森林。最干旱的站点（分类为“草地”和“非常干燥”）生产力受到了巨大影响，相对于干旱前的平均水平，两年内总初级生产力（GPP）下降了65%。然而，“干燥”、“季节性湿润”和“湿润”生态系统的通量表现出显著的抗性，GPP没有总体变化。所有站点恢复迅速；干旱后第一年的碳通量与气候相似的干旱前年份相当（并且通常超过）。干旱响应受到特定于生态系统的策略的强烈调节。最干旱的生态系统显示出生产力与水分可利用性的直接耦合，而中间生态系统（干燥和季节性湿润）利用储存的土壤水分在干旱期间维持蒸散和生产力。在这些站点，湿润期水分得以保存（尽管降雨充足，但蒸散 < 需求），干旱期水分被消耗（蒸散 > 降雨）。这种在高降雨变率下减轻周期性水分胁迫的机制可能促成了干燥和季节性湿润站点显著的抗旱能力。月度水分亏缺指数（MWDI）成为跨空间生产力的有力预测指标，突出表明短期水分可利用性亏缺对整个生态系统组成有强烈影响。对干旱响应机制的分析表明，水分胁迫下叶片迅速脱落，尤其是在最干旱的站点。我们的研究结果强调了在植被模型中考虑地下水分储存和多样干旱响应策略的重要性。我们提供了关键基准，以改进植物 - 水关系的参数化，有助于制定适应气候变化的稳健管理策略。
