Sun-Induced Fluorescence under a heat wave. Evidence from a tree-grass ecosystem
Abstract
Predicting the effect of climate extremes on ecosystem functioning is a highly relevant undertaking in global change ecology, especially as anthropogenic-induced climate change is contributing to more severe and frequent climate extremes. It is therefore necessary to develop remote sensing tools that allow to monitor the effect of extreme heat and drought on photosynthesis and transpiration at ecosystem and global scale.
Sun-induced fluorescence (SIF), the radiation flux emitted by plant chlorophylls molecules in the 650-800 nm spectral window, is considered a robust indicator of photosynthetic performance. Recently it has been shown that SIF can track changes in light use efficiency (LUE) and absorbed photosynthetic active radiation (APAR), and therefore it is a good predictor of gross primary production (GPP) and indirectly also transpiration (T). However, not enough has been investigated regarding the capacity of SIF to respond to extreme events such as heat waves and droughts. The European summer of 2018 was characterized by a heatwave, with unusually high air temperatures (Tair) and vapor pressure deficit (VPD) that affected most of Europe resulting in significant reduction in LAI and widespread plant mortality. In this contribution, by synthesizing information coming from eddy covariance (CO2, evapotranspiration fluxes, and GPP), SIF retrieved with the Fluorescence BOX (JB Hypespectral Devices) in the O2-A (∼760 nm) and O2-B (∼680 nm) absorption features, sap-flow measurements, and MONITORING-PAM (long-term monitoring of photosynthesis at leaf level through active fluorescence) in a Mediterranean tree grass ecosystem subject to the heat wave of 2018, we aim to quantify the effect of extreme Air temperature and VPD on SIF and its capacity to predict GPP and T. Results show that the heatwave, that because of the high intensity, but short duration caused mainly physiological rather than structural changes in the canopy, strongly affected both GPP and SIF. During the heatwave GPP and SIF exhibited a negative relationship, contrary to the positive relationship observed when the stress is absent. As the photochemical reflectance index (PRI) was the best predictor of GPP during the heatwave, it is hypothesized that during periods of extreme heat the preferred dissipation pathway is through non-photochemical quenching, or heat dissipation. A negative GPP-SIF relationship during stress has been hypothesized through modelling studies and empirically proven at leaf level, but to our knowledge it is the first time that is seen at canopy scale. The results show that SIF is physiologically regulated during extreme events, but alone is not sufficient to quantify photosynthetic activity during periods of high stress.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B11Q2282M
- Keywords:
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- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0480 Remote sensing;
- BIOGEOSCIENCES;
- 1615 Biogeochemical cycles;
- processes;
- and modeling;
- GLOBAL CHANGE