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Terrestrial carbon cycle models are routinely used to determine the response of the land carbon sink under expected future climate change, yet these predictions remain highly uncertain. Increasing the realism of processes in these models may help with predictive skill, but any such addition should be confronted with observations and evaluated in the context of the aggregate behavior of the carbon cycle. Here, two formulations for leaf area index (LAI) phenology are coupled to the same terrestrial biosphere model, one is climate agnostic and the other incorporates direct environmental controls on both timing and growth. Each model is calibrated simultaneously to observations of LAI, net ecosystem exchange (NEE), and biomass using the CARbon DAta-MOdel fraMework (CARDAMOM), and validated against withheld data including eddy covariance estimates of gross primary productivity (GPP) and ecosystem respiration (Re), across six ecosystems from the tropics to high-latitudes. Both model formulations show similar predictive skill for LAI and NEE. However, with the addition of direct environmental controls on LAI, the integrated model explains 22 % more variability in GPP and Re, and reduces biases in these fluxes by 58 % and 77 %, respectively, while also predicting more realistic annual litterfall rates, due to changes in carbon allocation and turnover. We extend this analysis to evaluate the inferred climate sensitivity of LAI and NEE with the new model, and show that the added complexity shifts the sign, magnitude, and seasonality of NEE sensitivity to precipitation and temperature. This highlights the benefit of process complexity when inferring underlying processes from Earth observations and in representing the climate response of the terrestrial carbon cycle.

Most Earth system models (ESMs) do not explicitly represent the carbon (C) costs of plant nutrient acquisition, which leads to uncertainty in predictions of the current and future constraints to the land C sink. While plants acquire nutrients through different uptake pathways, such as from mycorrhizae, direct root uptake, retranslocation from senescing tissues, and biological fixation in the case of nitrogen (N), they usually have different associated C costs. Determining the amount of nutrients acquired through each uptake pathway and the associated C cost could increase understanding of the global C and nutrient cycles, as well as the predictive skills of ESMs.Here, we integrate a plant productivity-optimizing nutrient (N and phosphorus (P)) acquisition model (Fixation & Uptake of Nutrients, FUN) into the Energy Exascale Earth System (E3SM) Land Model (ELM) to simulate the global C and nutrient cycles (Braghiere et al., 2022). We benchmarked the model with observations (in-situ, remotely sensed, and integrated using artificial intelligence), and other ESMs from CMIP6; we found significant improvements in present C cycle variables estimates. We also examine the impact of mycorrhizal spatial distributions on the global C cycle, since most plant species predominantly associate with a single type of mycorrhizal fungi and uncertainties in mycorrhizal distributions are non-trivial, with current estimates disagreeing in up to 50% over 40% of the land area (Braghiere et al., 2021). Global Net Primary Productivity (NPP) is reduced by 20% with N costs and 50% with NP costs, while modeled and observed nutrient limitation agreement increases when N and P are considered together. Even though NPP has been growing globally in response to increasing CO2, as soil nutrient progressively becomes more limiting, the costs to NPP for nutrient acquisition have increased at a faster rate. This suggests that nutrient acquisition will increasingly demand a higher portion of assimilated C to support the same productivity.Braghiere, et al. (2022) doi.org/10.1029/2022MS003204Braghiere, et al. (2021) doi.org/10.1029/2021GL094514

In vegetation canopies with complex architectures, diffuse solar radiation can enhance carbon assimilation through photosynthesis because isotropic light is able to reach deeper layers of the canopy. Although this effect has been studied in the past decade, the mechanisms and impacts of this enhancement over South America remain poorly understood. Over the Amazon deforestation arch large amounts of aerosols are released into the atmosphere due to biomass burning, which provides an ideal scenario for further investigation of this phenomenon in the presence of canopies with complex architecture. In this paper, the relation of aerosol optical depth and surface fluxes of mass and energy are evaluated over three study sites with artificial neural networks and radiative transfer modeling. Results indicate a significant effect of the aerosol on the flux of carbon dioxide between the vegetation and the atmosphere, as well as on energy exchange, including that surface fluxes are sensitive to second-order radiative impacts of aerosols on temperature, humidity, and friction velocity. CO2 exchanges increased in the presence of aerosol in up to 55 % in sites with complex canopy architecture. A decrease of approximately 12 % was observed for a site with shorter vegetation. Energy fluxes were negatively impacted by aerosols over all study sites.

Background and AimsImproved modelling of carbon assimilation and plant growth to low soil moisture requires evaluation of underlying mechanisms in the soil, roots, and shoots. The feedback between plants and their local environment throughout the whole spectrum soil-root-shoot-environment is crucial to accurately describe and evaluate the impact of environmental changes on plant development. This study presents a 3D functional structural plant model, in which shoot and root growth are driven by radiative transfer, photosynthesis, and soil hydrodynamics through different parameterisation schemes relating soil water deficit and carbon assimilation. The new coupled model is used to evaluate the impact of soil moisture availability on plant productivity for two different groups of flowering plants under different spatial configurations.MethodsIn order to address different aspects of plant development due to limited soil water availability, a 3D FSP model including root, shoot, and soil was constructed by linking three different well-stablished models of airborne plant, root architecture, and reactive transport in the soil. Different parameterisation schemes were used in order to integrate photosynthetic rate with root water uptake within the coupled model. The behaviour of the model was assessed on how the growth of two different types of plants, i.e. monocot and dicot, is impacted by soil water deficit under different competitive conditions: isolated (no competition), intra, and interspecific competition.Key ResultsThe model proved to be capable of simulating carbon assimilation and plant development under different growing settings including isolated monocots and dicots, intra, and interspecific competition. The model predicted that (1) soil water availability has a larger impact on photosynthesis than on carbon allocation; (2) soil water deficit has an impact on root and shoot biomass production by up to 90 % for monocots and 50 % for dicots; and (3) the improved dicot biomass production in interspecific competition was highly related to root depth and plant transpiration.ConclusionsAn integrated model of 3D shoot architecture and biomass development with a 3D root system representation, including light limitation and water uptake considering soil hydraulics, was presented. Plant-plant competition and regulation on stomatal conductance to drought were able to be predicted by the model. In the cases evaluated here, water limitation impacted plant growth almost 10 times more than the light environment.

Most tree species predominantly associate with a single type of mycorrhizal fungi, which can differentially 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. Here, 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, 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-that is, 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. U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program United States Department of Energy (DOE) [DE-SC0008317, DE-SC0016188]; NASA IDS program

Three-dimensional (3D) vegetation canopy structure plays an important role in the way radiation interacts with the land surface. Accurately representing this process in Earth System models (ESMs) is crucial for the modeling of the global carbon, energy, and water cycles and hence future climate projections. Despite the importance of accounting for 3D canopy structure, the inability to represent such complexity at regional and global scales has impeded a successful implementation into ESMs. An alternative approach is to use an implicit clumping index to account for the horizontal heterogeneity in vegetation canopy representations in ESMs at global scale. This paper evaluates how modeled hyperspectral shortwave radiation partitioning of the terrestrial biosphere, as well as Sun-Induced Chlorophyll Fluorescence (SIF) are impacted when a clumping index parameterization is incorporated in the radiative transfer scheme of a new generation ESM, the Climate Model Alliance (CliMA). An accurate hyperspectral radiative transfer representation within ESMs is critical for accurately using of satellite data to confront, constrain, and improve land model processes. The newly implemented scheme is compared to Monte Carlo calculations for idealized scenes from the Radiation transfer Model Intercomparison for the Project for Intercomparison of Land-Surface Parameterizations (RAMI4PILPS), for open forest canopies both with and without snow on the ground. Results indicate that it is critical to account for canopy structural heterogeneity when calculating hyperspectral radiation transfer. The RMSE in shortwave radiation is reduced for reflectance (25%), absorptance (66%), and transmittance (75%) compared to the scenario without considering clumping. Calculated SIF is validated against satellite remote sensing data with the recently launched NASA Orbiting Carbon Observatory (OCO) 3, showing that including vertical and horizontal canopy structure when deriving SIF can improve model predictions in up to 51% in comparison to the scenario without clumping. By adding a clumping index into the CliMA-Land model, the relationship between canopy structure and SIF, Gross Primary Productivity (GPP), hyperspectral radiative transfer, and viewing geometry at the canopy scale can be explored in detail.

At the leaf level, stomata control the exchange of water and carbon across the air-leaf interface. Stomatal conductance is typically modeled empirically, based on environmental conditions at the leaf surface. Recently developed stomatal optimization models show great skills at predicting carbon and water fluxes at both the leaf and tree levels. However, it has not been evaluated how well the optimization models perform at larger scales. Furthermore, stomatal models are often used with simple single-leaf representations of canopy radiative transfer (RT), such as big-leaf models. Nevertheless, the single-leaf canopy RT schemes do not have the capability to model optical properties of the leaves or the entire canopy. As a result, they are unable to evaluate the impact of vertical gradients within the canopy, or directly link canopy optical properties with light distribution within the canopy to remote sensing data observed from afar. Here we incorporated one optimization-based and two empirical stomatal models with a comprehensive RT model in the land component of a new Earth System model within CliMA, the Climate Modelling Alliance. The model allowed us to simultaneously simulate carbon and water fluxes as well as leaf and canopy reflectance and fluorescence spectra. We tested our model by comparing our modeled carbon and water fluxes and solar-induced chlorophyll fluorescence (SIF) to two flux tower observations (a gymnosperm forest and an angiosperm forest) and satellite SIF retrievals, respectively. All three stomatal models quantitatively predicted the carbon and water fluxes for both forests. The optimization model, in particular, showed increased skill in predicting the water flux given the lower error (c. 14.2 % and 21.8 % improvement for the gymnosperm and angiosperm forests, respectively) and better 1 : 1 comparison (slope increases from c. 0.34 to 0.91 for the gymnosperm forest, and from c. 0.38 to 0.62 for the angiosperm forest). Our model also predicted the SIF yield, quantitatively reproducing seasonal cycles for both forests. We found that using stomatal optimization with a comprehensive RT model showed high accuracy in simulating land surface processes. The ever-increasing number of regional and global datasets of terrestrial plants, such as leaf area index and chlorophyll contents, will help parameterize the land model and improve future Earth System modeling in general.

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. I will 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 will also cover how modeled carbon assimilation of the terrestrial biosphere is impacted when a satellite derived clumping index is incorporated into the UKESM. Finally, I will touch on how the clumping index might be integrated into hyperspectral ESMs to explore the theoretical relationship between canopy structure and photosynthesis.

Most tree species predominantly associate with a single type of mycorrhizal fungi. Because of the principle differences in mycorrhizal associations, they can differentially affect plant nutrient ac...

International audience; The impact of vegetation structure on the absorption of shortwave radiation in Earth System Models (ESMs) is potentially important for accurate modeling of the carbon cycle and hence climate projections. A proportion of incident shortwave radiation is used by plants to photosynthesize and canopy structure has a direct impact on the fraction of this radiation which is absorbed. This paper evaluates how modeled carbon assimilation of the terrestrial biosphere is impacted when clumping derived from satellite data is incorporated. We evaluated impacts of clumping on photosynthesis using the Joint UK Land Environment Simulator, the land surface scheme of the UK Earth System Model. At the global level, Gross Primary Productivity (GPP) increased by 5.53 +/- 1.02 PgC/year with the strongest absolute increase in the tropics. This is contrary to previous studies that have shown a decrease in photosynthesis when similar clumping data sets have been used to modify light interception in models. In our study additional transmission of light through upper canopy layers leads to enhanced absorption in lower layers in which photosynthesis tends to be light limited. We show that this result is related to the complexity of canopy scheme being used.

Addressing the impact of vegetation architecture on shortwave radiation transfer in land surface models is important for accurate weather forecasting, carbon budget estimates, and climate predictions. This paper investigates to what extent it is possible to retrieve structural parameters of two different parameterization schemes from direct transmittance derived from digital hemispherical photography and 3D radiative transfer modeling for two study sites with different vegetation canopy architectures. Neglecting the representation of 3D canopy structure in radiative transfer schemes leads to significant errors in shortwave radiation partitioning (up to 3.5 times more direct transmittance in the 3D model). Structural parameters, referred to as whole canopy ‘clumping indices’, were obtained in order to evaluate the impact of angular variation in clumping on shortwave radiation transfer. Impacts on photosynthesis were evaluated at site level with the UKESM land surface model, JULES. A comparison between flux tower derived and modeled photosynthesis indicates that considering zenith angular variations of structural parameters in the radiative transfer scheme of the UKESM land surface model significantly improves photosynthesis prediction in light limited ecosystems (from RMSE = 2.91 μmol CO2.m − 2.s − 1 to RMSE = 1.51 μmol CO2.m − 2.s − 1, 48% smaller), typically with enhanced photosynthesis from bottom layers.

A fast scheme is described to compute the 3-D interaction of solar radiation with vegetation canopies. The canopy is split in the horizontal plane into one clear region and one or more vegetated regions, and the two-stream equations are used for each, but with additional terms representing lateral exchange of radiation between regions that are proportional to the area of the interface between them. The resulting coupled set of ordinary differential equations is solved using the matrix-exponential method. The scheme is compared to solar Monte Carlo calculations for idealized scenes from the RAMI4PILPS intercomparison project, for open forest canopies and shrublands both with and without snow on the ground. Agreement is good in both the visible and infrared: for the cases compared, the root-mean-squared difference in reflectance, transmittance and canopy absorptance is 0.020, 0.038 and 0.033, respectively. The technique has potential application to weather and climate modelling.

A fast scheme is described to compute the 3D interaction of solar radiation with vegetation. The vegetation canopy is split horizontally into one clear region and one or more vegetated regions, and the two-stream equations are used for each, but with additional terms representing lateral exchange of radiation between regions that are proportional to the area of the interface between them. The resulting coupled set of ordinary differential equations is solved using the matrix-exponential method. The scheme is compared to solar Monte Carlo calculations for idealized scenes from the ‘RAMI4PILPS’ intercomparison project, for open forest canopies and shrublands both with and without snow on the ground. Agreement in reflectance, transmittance and canopy absorptance is excellent in both the visible and near infrared. The technique has potential application to weather and climate modelling.

Em dosséis com arquitetura foliar complexa, a radiação solar difusa pode potencializar a capacidade fotossintética, porque os penetra de modo mais eficiente. Apesar dos diversos estudos realizados nesse sentido em diferentes regiões do globo, os mecanismos e impactos do efeito da fertilização difusa sobre a América do Sul ainda continuam sendo pouco conhecidos. O Arco do Desflorestamento da Amazônia é um cenário ideal para sua maior investigação, tanto pela presença de complexos ecossistemas, quanto pela grande carga de aerossóis lançada para a atmosfera, em decorrência da queima de biomassa. Um estudo baseado em três diferentes localidades do Arco do Desflorestamento da Amazônia foi conduzido, a fim de relacionar a profundidade óptica dos aerossóis com alguns fluxos de superfície. Os resultados mostraram efeitos significativos da presença dos aerossóis tanto na troca de gás carbônico entre a vegetação e a atmosfera, quanto na troca de energia. Ainda, os fluxos mostraram ser sensíveis também às mudanças na temperatura, umidade e vento, além da influência do próprio ciclo diurno. Em cenários hipotéticos, foi possível isolar apenas o efeito do aerossol. O comportamento do fluxo de gás carbônico à presença dos aerossóis não foi o mesmo para as três localidades, o que indica uma grande dependência do fenômeno com as características da vegetação local. Na Reserva Biológica do Jaru e Ilha do Bananal, as trocas de gás carbônico entre a atmosfera e a superfície são favorecidas na presença de aerossóis, podendo atingir valores até 55% maiores em Jaru. Entretanto, Sinop apresentou uma redução de aproximadamente 12% no valor médio do fluxo de gás carbônico, para o período avaliado. Os fluxos de energia mostraram ser afetados negativamente pela presença dos aerossóis. Na Ilha do Bananal, a média do fluxo de calor sensível em cenários sem aerossóis foi em torno de 60% maior, e de até 13% maior para o fluxo de calor latente em Sinop. Devido aos processos de absorção e espalhamento da radiação solar pelos aerossóis, menos energia atinge a superfície e, portanto, há menos disponibilidade para a realização de tais trocas, como esperado. In complex architecture canopies, the diffuse solar radiation can enhance photosynthetic capacity, as it penetrates more efficiently on them. Although several studies have been conducted on this topic over the world, the mechanisms and impacts of the \"diffuse fertilization effect\" over South America still remains poorly understood. The Amazon Deforestation Arch provides an ideal scenario for its further investigation, by the presence of complex ecosystems and by the large amounts of aerosols released into the atmosphere due to biomass burning. A study based on three different sites in the Amazon Deforestation Arch was conducted in order to relate the aerosol optical depth with some surface fluxes. The results showed significant effects of the aerosol presence in both, the exchange of carbon dioxide between the vegetation and the atmosphere, and the energy exchange. Still, the fluxes also showed to be sensitive to changes in temperature, humidity and wind velocities, as well as the influence of the diurnal cycle itself. In hypothetical scenarios, it was possible to isolate only the aerosol effect. The carbon dioxide flux behavior due to the aerosol presence was not the same for all the three locations, showing that it depends on the local vegetation characteristics. At the Jaru Biological Reserve and Bananal Island, the carbonic gas exchanges between the atmosphere and the surface increased under the aerosol presence, achieving values up to 55% higher in Jaru. However, Sinop showed a decrease by approximately 12% in the average value of the carbon dioxide flux for the evaluated period. Energy fluxes showed to be 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 the aerosols, less energy reaches the surface, and therefore there is less availability to perform such exchanges, as expected.