Decoupling between stomatal conductance and photosynthesis occurs under extreme heat in broadleaf tree species regardless of water access

作者：Renée M. Marchin, Belinda E. Medlyn, Mark G. Tjoelker, David S. Ellsworth · 发表于：Global Change Biology · 年份：2023 · DOI：10.1111/gcb.16929 · 被引用次数：95 · 研究领域：Plant Water Relations and Carbon Dynamics、Tree-ring climate responses、Plant responses to elevated CO2

Abstract High air temperatures increase atmospheric vapor pressure deficit (VPD) and the severity of drought, threatening forests worldwide. Plants regulate stomata to maximize carbon gain and minimize water loss, resulting in a close coupling between net photosynthesis ( A net ) and stomatal conductance ( g s ). However, evidence for decoupling of g s from A net under extreme heat has been found. Such a response both enhances survival of leaves during heat events but also quickly depletes available water. To understand the prevalence and significance of this decoupling, we measured leaf gas exchange in 26 tree and shrub species growing in the glasshouse or at an urban site in Sydney, Australia on hot days (maximum T air > 40°C). We hypothesized that on hot days plants with ample water access would exhibit reduced A net and use transpirational cooling leading to stomatal decoupling, whereas plants with limited water access would rely on other mechanisms to avoid lethal temperatures. Instead, evidence for stomatal decoupling was found regardless of plant water access. Transpiration of well‐watered plants was 23% higher than model predictions during heatwaves, which effectively cooled leaves below air temperature. For hotter, droughted plants, the increase in transpiration during heatwaves was even more pronounced— g s was 77% higher than model predictions. Stomatal decoupling was found for most broadleaf evergreen and broadleaf deciduous species at the urban site, including...