Published September 2023 | Published
Journal Article Open

Elucidating climatic drivers of photosynthesis by tropical forests

  • 1. ROR icon California Institute of Technology
  • 2. ROR icon Jet Propulsion Lab
  • 3. ROR icon University of Lorraine
  • 4. ROR icon University of Exeter

Abstract

Tropical forests play a pivotal role in regulating the global carbon cycle. However, the response of these forests to changes in absorbed solar energy and water supply under the changing climate is highly uncertain. Three‐year (2018–2021) spaceborne high‐resolution measurements of solar‐induced chlorophyll fluorescence (SIF) from the TROPOspheric Monitoring Instrument (TROPOMI) provide a new opportunity to study the response of gross primary production (GPP) and more broadly tropical forest carbon dynamics to differences in climate. SIF has been shown to be a good proxy for GPP on monthly and regional scales. Combining tropical climate reanalysis records and other contemporary satellite products, we find that on the seasonal timescale, the dependence of GPP on climate variables is highly heterogeneous. Following the principal component analyses and correlation comparisons, two regimes are identified: water limited and energy limited. GPP variations over tropical Africa are more correlated with water‐related factors such as vapor pressure deficit (VPD) and soil moisture, while in tropical Southeast Asia, GPP is more correlated with energy‐related factors such as photosynthetically active radiation (PAR) and surface temperature. Amazonia is itself heterogeneous: with an energy‐limited regime in the north and water‐limited regime in the south. The correlations of GPP with climate variables are supported by other observation‐based products, such as Orbiting Carbon Observatory‐2 (OCO2) SIF and FluxSat GPP. In each tropical continent, the coupling between SIF and VPD increases with the mean VPD. Even on the interannual timescale, the correlation of GPP with VPD is still discernable, but the sensitivity is smaller than the intra‐annual correlation. By and large, the dynamic global vegetation models in the TRENDY v8 project do not capture the high GPP seasonal sensitivity to VPD in dry tropics. The complex interactions between carbon and water cycles in the tropics illustrated in this study and the poor representation of this coupling in the current suite of vegetation models suggest that projections of future changes in carbon dynamics based on these models may not be robust.

Copyright and License

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Acknowledgement

This work was funded by the President's and Director's Research and Development Fund at the NASA-sponsored Jet Propulsion Laboratory (JPL) and California Institute of Technology. We also want to acknowledge the financial support from NASA Carbon Cycle Ecosystem program. The work done at the eddy flux tower in French Guiana was supported by two grants overseen by the French National Research Agency (ANR) as part of the “Investissements d'Avenir” program (ARBRE: ANR-11-LABX-0002-01, CEBA: ANR-10-LABX-25-01). The satellite products, reanalysis data, and TRENDY model output used for this research can be downloaded from the website at http://web.gps.caltech.edu/~yzw/share/GCB-2021. The TROPOMI SIF data can be accessed through ftp://fluo.gps.caltech.edu/data/tropomi/. All requests for materials in this paper should be addressed to Yuan Wang (yzwang@stanford.edu).

Data Availability

The data that support the findings of this study are available from Zenodo at GCB-23-0221.R1.

Supplemental Material

Data S1 (PDF)

Files

Global Change Biology - 2023 - Wang - Elucidating climatic drivers of photosynthesis by tropical forests.pdf

Additional details

Created:
January 24, 2025
Modified:
January 24, 2025