Diverse responses of canopy conductance to heatwaves

Abstract

Heatwaves have increased significantly in recent decades, seriously affecting the biosphere. The vegetation canopy is altered by heatwaves through high temperatures and water deficit, adversely affecting the ecosystem's health. However, how the canopy resilience of different ecosystems responding to heatwaves behaves remains less understood. Canopy conductance (Gc) couples the carbon and water cycles and is often used as a proxy for vegetation activity. Here we used eddy-covariance (EC) flux observations and a diagnostic evapotranspiration model to deduce daily canopy conductance inversely. Total 16 flux sites from 2003 to 2014 were used to explore the changes in canopy conductance during heatwaves across multiple ecosystems. Our results showed that the frequency of heatwaves increased significantly in almost all EC sites, and the average heatwave trend was 0.4 d yr−1 (p < 0.05). Wetlands had the best resilience to heatwaves, as indicated by the Gc decreasing by 4.6% during heatwaves. For forest ecosystems, the Gc of evergreen broadleaf forests decreased by 29.3% during heatwaves, meaning they showed the best resilience to drought. This is followed by the deciduous broadleaf forests and evergreen needleleaf forests, whose Gc decreased by 50.7% and 46.3%, respectively. The above results suggest that the resilience of different ecosystems appears diverse during heatwaves. The wetter the ecosystem, the more resistant it is to heatwaves. This study highlights the distinct responses of ecosystems to heatwaves, facilitating our understanding of the influences heatwaves have on terrestrial ecosystems.