Modelling sun-induced fluorescence and photosynthesis with a land surface model at local and regional scales in northern Europe

Tea Thum,Luis Guanter,Christiaan Van Der Tol,Tuomas Laurila,Tiina Markkanen,Tuula Aalto,Sönke Zaehle,Philipp Köhler,Federico Magnani,Pasi Kolari,Annalea Lohila,Mika Aurela

doi:10.5194/bg-14-1969-2017

Abstract

Abstract. Recent satellite observations of sun-induced chlorophyll fluorescence (SIF) are thought to provide a large-scale proxy for gross primary production (GPP), thus providing a new way to assess the performance of land surface models (LSMs). In this study, we assessed how well SIF is able to predict GPP in the Fenno-Scandinavian region and what potential limitations for its application exist. We implemented a SIF model into the JSBACH LSM and used active leaf-level chlorophyll fluorescence measurements (Chl F) to evaluate the performance of the SIF module at a coniferous forest at Hyytiälä, Finland. We also compared simulated GPP and SIF at four Finnish micrometeorological flux measurement sites to observed GPP as well as to satellite-observed SIF. Finally, we conducted a regional model simulation for the Fenno-Scandinavian region with JSBACH and compared the results to SIF retrievals from the GOME-2 (Global Ozone Monitoring Experiment-2) space-borne spectrometer and to observation-based regional GPP estimates. Both observations and simulations revealed that SIF can be used to estimate GPP at both site and regional scales. At regional scale the model was able to simulate observed SIF averaged over 5 years with r2 of 0.86. The GOME-2-based SIF was a better proxy for GPP than the remotely sensed fAPAR (fraction of absorbed photosynthetic active radiation by vegetation). The observed SIF captured the seasonality of the photosynthesis at site scale and showed feasibility for use in improving of model seasonality at site and regional scale.

Highlights

The terrestrial biosphere is thought to store approximately a quarter of the carbon dioxide (CO2) released by anthropogenic activity (Le Quéré et al, 2016)
The leaf-level measurements provided the first comparison to simulations and it is essential that site-level sun-induced chlorophyll fluorescence (SIF) observations are available, such as in study by Yang et al (2015)
– JSBACH was better in simulation of SIF than fraction of absorbed photosynthetically active radiation (fAPAR) at the site scale

Summary

Introduction

The terrestrial biosphere is thought to store approximately a quarter of the carbon dioxide (CO2) released by anthropogenic activity (Le Quéré et al, 2016). A detailed spatio-temporal distribution of this uptake is absent, partly due to an incomplete understanding of the terrestrial carbon balance as a whole. Estimates of the terrestrial net carbon balance are often made by land surface models (LSMs) (Sitch et al, 2015). Assessing and improving the performance of LSMs at larger scales remains a challenge, as limited data sources for large-scale carbon dioxide flux estimates are available (Luo et al, 2012). Previous global estimates of the spatial distribution and the variability of plant photosynthetic production have mostly been based on remote sensing of vegetation greenness (such as the normalized difference vegetation index, NDVI) or the fraction of absorbed photosynthetically active radiation (fAPAR) describing how much of the incoming photosynthet-

Methods

Results

Discussion

Conclusion