Sensitivity of vegetation structural and physiological information to compound drought and heatwave stress based on Solar-induced chlorophyll fluorescence (SIF)

Sun-induced chlorophyll fluorescence (SIF) measurements have shown unique potential for quantifying both plant physiological and structural stress under compound drought and heatwave events. However, there is a lack of understanding and well explore of the differences in the sensitivity of vegetation physiological and structural information based on solar-induced chlorophyll fluorescence (SIF) to compound drought and heatwave stresses and the driving mechanisms behind it. The aim of this study was to assess whether SIF-derived physiological information (eΦF) and structural information (NIRvP) could improves the quantification of physiological and structural aspects of vegetation sensitivity to compound drought and heatwave stress at the mid-high latitudes of northern hemisphere by using contiguous sun-induced fluorescence (CSIF) data, respectively. We found that, compared to the vegetation sturctural information (NIRvP), the relative importance of vegetation physiological information (eΦF) to eCSIF variability increases 6.5% to14.8% under compound drought a heatwave stresses in all regions, which confirms the contribution of physiological variation to eSIF. We further demonstrated that vegetation physiological information (eΦF) can better detect compound drought and heatwave stress in humid regions and forest ecosystems, which is mainly driven by physiological (LCC and VCmax) and environmental (VPD and SR) factors; whereas vegetation physiological information (eΦF) and structural information (NIRvP) have similar ability to capture compound drought and heatwave stresses. The lines of evidence suggested that utilizing eΦF for physiological investigations and NIRvP for structural information will contribute to improve our comprehensive understanding of vegetation physiological and structural responses to simultaneous high-temperature and high-drought stresses.