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

Getachew Mengistu, Anteneh ; Mengistu Tsidu, Gizaw ; Koren, Gerbrand ; Kooreman, Maurits L. ; Folkert Boersma, K. ; Tagesson, Torbern LU ; Ardö, Jonas LU orcid ; Nouvellon, Yann and Peters, Wouter (2021) In Biogeosciences 18(9). p.2843-2857
Abstract
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... (More)
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. (Less)
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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Biogeosciences
volume
18
issue
9
pages
15 pages
publisher
Copernicus GmbH
external identifiers
  • scopus:85105871699
ISSN
1726-4170
DOI
10.5194/bg-18-2843-2021
language
English
LU publication?
yes
id
f359598e-721d-4d09-9892-b8eb4ff4cb63
date added to LUP
2021-06-01 11:18:43
date last changed
2023-02-21 10:42:42
@article{f359598e-721d-4d09-9892-b8eb4ff4cb63,
  abstract     = {{The carbon cycle of tropical terrestrial vegetation plays a vital role in the storage and exchange of atmospheric CO<sub>2</sub>. But large uncertainties surround the impacts of land-use change emissions, climate warming, the frequency of droughts, and CO<sub>2</sub> 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 CO<sub>2</sub>, 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 &gt;0.9 (<i>N</i>=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 (<i>R</i>&gt;0.9; <i>N</i>≥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.}},
  author       = {{Getachew Mengistu, Anteneh and Mengistu Tsidu, Gizaw and Koren, Gerbrand and Kooreman, Maurits L. and Folkert Boersma, K. and Tagesson, Torbern and Ardö, Jonas and Nouvellon, Yann and Peters, Wouter}},
  issn         = {{1726-4170}},
  language     = {{eng}},
  month        = {{05}},
  number       = {{9}},
  pages        = {{2843--2857}},
  publisher    = {{Copernicus GmbH}},
  series       = {{Biogeosciences}},
  title        = {{Sun-induced fluorescence and near-infrared reflectance of vegetation track the seasonal dynamics of gross primary production over Africa}},
  url          = {{http://dx.doi.org/10.5194/bg-18-2843-2021}},
  doi          = {{10.5194/bg-18-2843-2021}},
  volume       = {{18}},
  year         = {{2021}},
}