Li Yafei, Eugster Werner, Riedl Andreas, Lehmann Marco M, Aemisegger Franziska, Buchmann Nina
Institute of Agricultural Sciences, ETH Zurich, Zurich, Switzerland.
Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Birmensdorf, Switzerland.
Front Plant Sci. 2023 May 9;14:1136037. doi: 10.3389/fpls.2023.1136037. eCollection 2023.
Increasing frequencies of heatwaves combined with simultaneous drought stress in Europe threaten the ecosystem water and carbon budgets of alpine grasslands. Dew as an additional water source can promote ecosystem carbon assimilation. It is known that grassland ecosystems keep high evapotranspiration as long as soil water is available. However, it is rarely being investigated whether dew can mitigate the impact of such extreme climatic events on grassland ecosystem carbon and water exchange. Here we use stable isotopes in meteoric waters and leaf sugars, eddy covariance fluxes for HO vapor and CO, in combination with meteorological and plant physiological measurements, to investigate the combined effect of dew and heat-drought stress on plant water status and net ecosystem production (NEP) in an alpine grassland (2000 m elevation) during the June 2019 European heatwave. Before the heatwave, enhanced NEP in the early morning hours can be attributed to leaf wetting by dew. However, dew benefits on NEP were cancelled out by the heatwave, due to the minor contribution of dew in leaf water. Heat-induced reduction in NEP was intensified by the combined effect of drought stress. The recovery of NEP after the peak of the heatwave could be linked to the refilling of plant tissues during nighttime. Among-genera differences of plant water status affected by dew and heat-drought stress can be attributed to differences in their foliar dew water uptake, and their reliance on soil moisture or the impact of the atmospheric evaporative demand. Our results indicate that dew influence on alpine grassland ecosystems varies according to the environmental stress and plant physiology.
在欧洲，热浪发生频率不断增加，同时伴随着干旱胁迫，这对高山草甸的生态系统水分和碳收支构成了威胁。露水作为额外的水源可以促进生态系统的碳同化。众所周知，只要土壤中有水，草地生态系统就会保持较高的蒸散量。然而，露水是否能够减轻此类极端气候事件对草地生态系统碳和水分交换的影响，这方面的研究却很少。在此，我们利用大气降水和叶片糖分中的稳定同位素、水汽和二氧化碳的涡度相关通量，结合气象和植物生理测量数据，来研究在2019年6月欧洲热浪期间，露水和热旱胁迫对海拔2000米的高山草甸植物水分状况和生态系统净生产力（NEP）的综合影响。在热浪来临之前，清晨时分NEP的增加可归因于露水使叶片湿润。然而，由于露水在叶片水分中所占比例较小，热浪抵消了露水对NEP的益处。干旱胁迫的综合作用加剧了热浪导致的NEP下降。热浪高峰期过后NEP的恢复可能与夜间植物组织的再补水有关。受露水和热旱胁迫影响的植物水分状况在属间存在差异，这可归因于它们叶片对露水的吸收、对土壤水分的依赖程度或大气蒸发需求的影响。我们的结果表明，露水对高山草甸生态系统的影响会因环境胁迫和植物生理状况而有所不同。
