Research

Global Earth System Modelling

Global distribution of climatic constraints (radiation, temperature, and precipitation) from WATCH-Forcing-Data-ERA-Interim data set to gross primary productivity from FLUXNET-MTE data for the year of 2008.
Fig3c_difference_gpp_clump_default_jules
Difference in GPP between JULES with clumping and JULES without clumping. Global average values are indicated at the bottom of the figures in PgC yr-1 with the 95% confidence interval. Grey areas represent regions with no data. From Braghiere et al. (2019).

Most tree species predominantly associate with a single type of mycorrhizal fungi, which can affect plant nutrient acquisition and biogeochemical cycling. Uncertainties in mycorrhizal distributions are non-trivial and current estimates disagree in up to 50% over 40% of the land area, including tropical forests. Remote sensing capabilities for mycorrhizal detection show promise for refining these estimates further. We address for the first time the impact of mycorrhizal distributions on global carbon and nutrient cycling. Using the state-of-the-art carbon-nitrogen economics within the Community Land Model version 5 (CLM5) we found Net Primary Productivity (NPP) increased throughout the 21st century by 20%; however, as soil nitrogen has progressively become limiting, the costs to NPP for nitrogen acquisition — i.e., to mycorrhizae — have increased at a faster rate by 60%. This suggests that nutrient acquisition will increasingly demand a higher portion of assimilated carbon to support the same productivity.

Nitrogen_limitation
(a) Risk of nitrogen limitation. Areas in red indicate higher risk of nitrogen limitation for NPP, and areas in blue indicate lower risk of nitrogen limitation for NPP; (b) The impact of climate change on ECM fraction (%) derived from Steidinger et al. (2019) for 2070 following the RCP8.5 with CMIP5 simulations; (c) Difference in NPP (gC m−2 yr−1) for future simulations (2016–2075) between projected future map generated for the year of 2070 and the present-day map C (Steidinger et al., 2019). The projected runs with CLM5 followed the SSP5 scenario in combination with RCP8.5 climate forcing from CESM2, member of CMIP6 simulations.

Braghiere, R. K., Fisher, J. B., Allen, K., Brzostek, E., Shi, M., Yang, X., Ricciuto, D.M., Fisher, R.A., Zhu, Q., Phillips, R.P., 2022. Modeling Global Carbon Costs of Plant Nitrogen and Phosphorus Acquisition. J. Adv. Model. Earth Syst. 14, e2022MS003204, https://doi.org/10.1029/2022MS003204

Braghiere, R. K., Fisher, J. B., Fisher, R. A., Shi, M., Steidinger, B. S., Sulman, B. N., Soudzilovskaia, N. A., Yang, X., Liang, J., Peay, K. G., Crowther, T. W. and Phillips, R. P., 2021. Mycorrhizal Distributions Impact Global Patterns of Carbon and Nutrient Cycling, Geophys. Res. Lett., 48(19), https://doi.org/10.1029/2021GL094514

Braghiere, R. K., Wang, Y., Doughty, R., Sousa, D., Magney, T., Widlowski, J.-L., Longo, M., Bloom, A.A., Worden, J., Gentine, P., Frankenberg, C., 2021. Accounting for canopy structure improves hyperspectral radiative transfer and sun-induced chlorophyll fluorescence representations in a new generation Earth System model. Remote Sens. Environ. 261, 112497. https://doi.org/10.1016/j.rse.2021.112497

Braghiere, R. K., Quaife, T., Black, E., He, L., and Chen, J. M.: Underestimation of Global Photosynthesis in Earth System Models Due to Representation of Vegetation Structure. Global Biogeochemical Cycles, 2018GB006135. https://doi.org/10.1029/2018GB006135, 2019.

Hogan, R. J., Quaife, T., and Braghiere, R.: Fast matrix treatment of 3-D radiative transfer in vegetation canopies: SPARTACUS-Vegetation 1.1, Geosci. Model Dev., 11, 339-350, https://doi.org/10.5194/gmd-11-339-2018, 2018.

 

Field work

Tropical forest

Uatumã Reserve, Amazon, Brazil. 2013.
Flux tower in Uatumã Reserve, Amazon, Brazil. 2013.

The effects of biomass burning aerosols on energy and mass fluxes in the Amazon

In vegetation canopies with complex architecture, diffuse solar radiation can enhance photosynthesis. Although studies have shown evidence on this, the mechanisms and impacts of the fertilisation effect of diffuse radiation in the Amazon rainforest still remains poorly understood. This  study was conducted  in three different sites in the Amazon Deforestation Arch in Brazil in order to estimate the impact of aerosol optical depth on surface fluxes.
 
Results indicate significant effects of the aerosol on fluxes of carbon dioxide, heat, and water. Fluxes are sensitive to temperature, humidity and wind speed, as well as the influence of the diurnal cycle itself. Experimental modelling scenarios were created in order to isolate the effect of aerosols. In the Jaru Biological Reserve and Bananal Island, flux of CO2 between the atmosphere and the surface increased in the presence of aerosol by up to 55% higher in Jaru, indicating an increase in carbon uptake by these forests. However, in Sinop a decrease was observed over the same period.
 
Fluxes of heat and water were negatively affected by the presence of aerosols. In the Bananal Island the average of sensitive heat flux in scenarios without aerosols was around 60% higher, and up to 13% higher for the latent heat flux in Sinop. Due to absorption and scattering of solar radiation by aerosols, less energy reaches the surface, and therefore less radiation is available at the surface.

Braghiere, R.K., Yamasoe MA, do Rosário NM, da Rocha H, de Souza Nogueira J, de Araújo AC. 2020. Characterization of the radiative impact of aerosols on CO2 and energy fluxes in the Amazon deforestation arch using artificial neural networks. Atmospheric Chemistry and Physics 20: 3439–3458. doi:10.5194/acp-20-3439-2020

Braghiere, R.K., Yamasoe, M.A., 2013.: Evaluation of CO2 flux modification as a function of aerosol optical depth at Bananal Island, Tocantins, Brazil, in: AIP Conference Proceedings. pp. 552–555. doi:10.1063/1.4804829

Other forest types

Addressing the impact of 3D vegetation structure on shortwave radiation transfer in Earth System Models (ESMs) is important for accurate weather forecasting, carbon budget estimates, and climate predictions. While leaf-level photosynthesis is well characterized and understood, estimates of global level carbon assimilation in the literature range from 110 to 175 PgC.yr-1. In this NASA JPL Carbon Club presentation, I explore how neglecting canopy structure leads to significant uncertainties in shortwave radiation partitioning, as well as second order derived canopy properties, such as leaf area index (LAI). I compare two different parameterization schemes of clumping index retrieved from digital hemispherical photography and 3D radiative transfer modeling over flux-tower sites in North America. Finally, I touch on how the clumping index might be integrated into hyperspectral ESMs to explore the theoretical relationship between canopy structure and photosynthesis, as well as estimates of vegetation indices, such as NDVI, NIRv, and SIF.

Braghiere, R. K., Quaife, T., Black, E., Ryu, Y., Chen, Q., Kauwe, M. G. De, & Baldocchi, D. (2020). Influence of sun zenith angle on canopy clumping and the resulting impacts on photosynthesis. Agricultural and Forest Meteorology, 291(May), 108065. doi:10.1016/j.agrformet.2020.108065

Boreal forest

Flux tower in Hyytiälä, Finland. 2017.
Siikaneva flux tower in a large open peatland, Finland. 2017.