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

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 Forestry Heatwave 04 agricultural and veterinary sciences 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
DOI: 10.1111/nph.17920 Publication Date: 2021-12-18T06:24:23Z
ABSTRACT
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.
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