Sun-induced fluorescence and near-infrared reflectance of vegetation track the seasonal dynamics of gross primary production over Africa

Mengistu Anteneh Getachew, Mengistu Tsidu Gizaw, Koren Gerbrand, Kooreman Maurits L., Boersma K. Folkert, Tagesson Torbern, Ardö Junas, Nouvellon Yann, Peters Wouter. 2021. Sun-induced fluorescence and near-infrared reflectance of vegetation track the seasonal dynamics of gross primary production over Africa. Biogeosciences, 18 (9) : 2843-2857.

Quartile : Q1, Sujet : ECOLOGY / Quartile : Q1, Sujet : GEOSCIENCES, MULTIDISCIPLINARY

Résumé : The carbon cycle of tropical terrestrial vegetation plays a vital role in the storage and exchange of atmospheric CO2. But large uncertainties surround the impacts of land-use change emissions, climate warming, the frequency of droughts, and CO2 fertilization. This culminates in poorly quantified carbon stocks and carbon fluxes even for the major ecosystems of Africa (savannas and tropical evergreen forests). Contributors to this uncertainty are the sparsity of (micro-)meteorological observations across Africa's vast land area, a lack of sufficient ground-based observation networks and validation data for CO2, and incomplete representation of important processes in numerical models. In this study, we therefore turn to two remotely sensed vegetation products that have been shown to correlate highly with gross primary production (GPP): sun-induced fluorescence (SIF) and near-infrared reflectance of vegetation (NIRv). The former is available from an updated product that we recently published (Sun-Induced Fluorescence of Terrestrial Ecosystems Retrieval – SIFTER v2), which specifically improves retrievals in tropical environments. A comparison against flux tower observations of daytime-partitioned net ecosystem exchange from six major biomes in Africa shows that SIF and NIRv reproduce the seasonal patterns of GPP well, resulting in correlation coefficients of >0.9 (N=12 months, four sites) over savannas in the Northern and Southern hemispheres. These coefficients are slightly higher than for the widely used Max Planck Institute for Biogeochemistry (MPI-BGC) GPP products and enhanced vegetation index (EVI). Similarly to SIF signals in the neighboring Amazon, peak productivity occurs in the wet season coinciding with peak soil moisture and is followed by an initial decline during the early dry season, which reverses when light availability peaks. This suggests similar leaf dynamics are at play. Spatially, SIF and NIRv show a strong linear relation (R>0.9; N≥250 pixels) with multi-year MPI-BGC GPP even within single biomes. Both MPI-BGC GPP and the EVI show saturation relative to peak NIRv and SIF signals during high-productivity months, which suggests that GPP in the most productive regions of Africa might be larger than suggested.

Mots-clés Agrovoc : végétation, production primaire, télédétection, Réflectance, fluorescence, variation saisonnière, indice de végétation, cycle du carbone

Mots-clés géographiques Agrovoc : Afrique

Mots-clés complémentaires : fluorescence induite par le soleil

Mots-clés libres : Gross primary productivity, Remote Sensing, Sun-induced fluorescence, Near-infrared reflectance, Africa

Classification Agris : U30 - Méthodes de recherche
P01 - Conservation de la nature et ressources foncières

Champ stratégique Cirad : CTS 1 (2019-) - Biodiversité

Agences de financement européennes : European Research Council

Programme de financement européen : H2020

Projets sur financement : (EU) New constraints on the Amazonian carbon balance from airborne observations of the stable isotopes of CO2

Auteurs et affiliations

• Mengistu Anteneh Getachew, Addis Ababa University (ETH) - auteur correspondant
• Mengistu Tsidu Gizaw, Addis Ababa University (ETH)
• Koren Gerbrand, Wageningen University (NLD)
• Kooreman Maurits L., Royal Netherlands Meteorological Institute (NLD)
• Boersma K. Folkert, Wageningen University (NLD)
• Tagesson Torbern, Lund University (SWE)
• Ardö Junas, Lund University (SWE)
• Nouvellon Yann, CIRAD-PERSYST-UMR Eco&Sols (THA)
• Peters Wouter, Wageningen University (NLD)

Source : Cirad-Agritrop (https://agritrop.cirad.fr/598235/)

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