Heatwave breaks down the linearity between sun‐induced fluorescence and gross primary production

• DOI: 10.1111/nph.17920
• Publication Date: 2021-12-18T06:24:23Z
• Authors: David Martini; Karolina Sakowska; Georg Wohlfahrt; Javier Pacheco‐La...; Christiaan van de...; Albert Porcar‐Cas...; Troy S. Magney; Arnaud Carrara; Roberto Colombo; Tarek S. El‐Madany; Rosario Gonzalez‐...; María Pilar Martín; Tommaso Julitta; Gerardo Moreno; Uwe Rascher; Markus Reichstein; Micol Rossini; Mirco Migliavacca
• Keywords: Chlorophyll; extreme events; gross primary production (GPP); heatwave; nonphotochemical quenching; photosynthesis; sun-induced fluorescence; extreme events; photosynthesis; gross primary production (GPP); sun-induced fluorescence; info:eu-repo/classification/ddc/580; 0207 environmental engineering; Forestry; Heatwave; 04 agricultural and veterinary sciences; 02 engineering and technology; 15. Life on land; Fluorescence; nonphotochemical quenching; Ecology, evolutionary biology; 13. Climate action; ITC-ISI-JOURNAL-ARTICLE; 0401 agriculture, forestry, and fisheries; ddc:580; Seasons; Photosynthesis; extreme events; gross primary production (GPP); heatwave; nonphotochemical quenching; photosynthesis; sun-induced fluorescence;; Ecosystem; Environmental Monitoring

Summary

Sun‐induced fluorescence in the far‐red region (SIF) is increasingly used as a remote and proximal‐sensing tool capable of tracking vegetation gross primary production (GPP). However, the use of SIF to probe changes in GPP is challenged during extreme climatic events, such as heatwaves. Here, we examined how the 2018 European heatwave (HW) affected the GPP–SIF relationship in evergreen broadleaved trees with a relatively invariant canopy structure. To do so, we combined canopy‐scale SIF measurements, GPP estimated from an eddy covariance tower, and active pulse amplitude modulation fluorescence. The HW caused an inversion of the photosynthesis–fluorescence relationship at both the canopy and leaf scales. The highly nonlinear relationship was strongly shaped by nonphotochemical quenching (NPQ), that is, a dissipation mechanism to protect from the adverse effects of high light intensity. During the extreme heat stress, plants experienced a saturation of NPQ, causing a change in the allocation of energy dissipation pathways towards SIF. Our results show the complex modulation of the NPQ–SIF–GPP relationship at an extreme level of heat stress, which is not completely represented in state‐of‐the‐art coupled radiative transfer and photosynthesis models.