A soil-plant-atmosphere continuum (SPAC) model for simulating tree transpiration with a soil multi-compartment solution

García-Tejera, Omar; López-Bernal, Álvaro; Testi, Luca; Villalobos, Francisco J.

doi:10.1007/s11104-016-3049-0

Cited by 32 publications

(20 citation statements)

References 52 publications

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“…A mechanistic SPAC model was used to simulate exchanges of CO 2 and H 2 O at the Lägeren forest site. The applied SPAC model was proposed by Garcia‐Tejera, Lopez‐Bernal, Testi, and Villalobos () and allows calculating the water transport in plants based on water potential (ψ) gradients from the soil (ψ s ) to the leaf (ψ l ) along with A n and T as well as underlying physiological parameters (i.e. maximum carboxylation rate [VC max ], maximum electron transport rate [ J max ], the Michaelis–Menten constants K C and K O , light compensation point [Γ], g s , leaf internal CO 2 [ C i ] and respiration [ R d ]).…”

Section: Methodsmentioning

confidence: 99%

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Remote sensing of forest gas exchange: Considerations derived from a tomographic perspective

Damm

Paul‐Limoges

Kükenbrink

et al. 2020

Global Change Biology

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The global exchange of gas (CO2, H2O) and energy (sensible and latent heat) between forest ecosystems and the atmosphere is often assessed using remote sensing (RS) products. Although these products are essential in quantifying the spatial variability of forest–atmosphere exchanges, large uncertainties remain from a measurement bias towards top of canopy fluxes since optical RS data are not sensitive for the vertically integrated forest canopy. We hypothesize that a tomographic perspective opens new pathways to advance upscaling gas exchange processes from leaf to forest stands and larger scales. We suggest a 3D modelling environment comprising principles of ecohydrology and radiative transfer modelling with measurements of micrometeorological variables, leaf optical properties and forest structure, and assess 3D fields of net CO2 assimilation (An) and transpiration (T) in a Swiss temperate forest canopy. 3D simulations were used to quantify uncertainties in gas exchange estimates inherent to RS approaches and model assumptions (i.e. a big‐leaf approximation in modelling approaches). Our results reveal substantial 3D heterogeneity of forest gas exchange with top of canopy An and T being reduced by up to 98% at the bottom of the canopy. We show that a simplified use of RS causes uncertainties in estimated vertical gas exchange of up to 300% and that the spatial variation of gas exchange in the footprint of flux towers can exceed diurnal dynamics. We also demonstrate that big‐leaf assumptions can cause uncertainties up to a factor of 10 for estimates of An and T. Concluding, we acknowledge the large potential of 3D assessments of gas exchange to unravelling the role of vertical variability and canopy structure in regulating forest–atmosphere gas and energy exchange. Such information allows to systematically link canopy with global scale controls on forest functioning and eventually enables advanced understanding of forest responses to environmental change.

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Section: Methodsmentioning

confidence: 99%

“…both differ less than 1%) (cf. Garcia‐Tejera et al, for a process chart). Afterwards, g s is scaled with the actual leaf area index (LAI) to obtain canopy conductance g c and used to obtain canopy T and A n with

A_{normaln} = g_{normalc} false(C_{a} - C_{i} false) + R_{normald},

T = g_{normalc} 1.6 \frac{VPD}{P},

where VPD is the vapour pressure deficit and P is the air pressure.…”

Section: Methodsmentioning

confidence: 99%

Remote sensing of forest gas exchange: Considerations derived from a tomographic perspective

Damm

Paul‐Limoges

Kükenbrink

et al. 2020

Global Change Biology

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“…By exploring only short-term salinity exposure, the proposed approach focuses on physiological mechanisms and allows us to momentarily neglect the morphological ones where acclimation becomes necessary. Future work will consider soil-root and multi-canopy layers (Williams et al, 1996;Siqueira et al, 2008;Bonan et al, 2014;Garc ıa-Tejera et al, 2017;Manoli et al, 2017) as well as variable sources and sinks of sucrose along the phloem. A further extension of this model can account for dynamic soil water and salt mass balance (Daly et al, 2004;Bartlett et al, 2014;Hartzell et al, 2018).…”

Section: Model Limitationsmentioning

confidence: 99%

Xylem–phloem hydraulic coupling explains multiple osmoregulatory responses to salt stress

2019

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Summary Salinity is known to affect plant productivity by limiting leaf‐level carbon exchange, root water uptake, and carbohydrates transport in the phloem. However, the mechanisms through which plants respond to salt exposure by adjusting leaf gas exchange and xylem–phloem flow are still mostly unexplored. A physically based model coupling xylem, leaf, and phloem flows is here developed to explain different osmoregulation patterns across species. Hydraulic coupling is controlled by leaf water potential, ψl, and determined under four different maximization hypotheses: water uptake (1), carbon assimilation (2), sucrose transport (3), or (4) profit function – i.e. carbon gain minus hydraulic risk. All four hypotheses assume that finite transpiration occurs, providing a further constraint on ψl. With increasing salinity, the model captures different transpiration patterns observed in halophytes (nonmonotonic) and glycophytes (monotonically decreasing) by reproducing the species‐specific strength of xylem–leaf–phloem coupling. Salt tolerance thus emerges as plant's capability of differentiating between salt‐ and drought‐induced hydraulic risk, and to regulate internal flows and osmolytes accordingly. Results are shown to be consistent across optimization schemes (1–3) for both halophytes and glycophytes. In halophytes, however, profit‐maximization (4) predicts systematically higher ψl than (1–3), pointing to the need of an updated definition of hydraulic cost for halophytes under saline conditions.

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“…Numerous models of varying complexity have been developed to study the hydrologic processes in the rhizosphere including the two-way feedback between the root xylem and the soil. Some models use a circuit analogy to simulate the flow of water through the network of xylem conduits (Christoffersen et al 2016;Garcia-Tejera et al 2017;Manoli et al 2017;Sperry et al 1998). The soil compartments in these models are often simplified shells surrounding onedimensional (1D) root layers.…”

Section: Introductionmentioning

confidence: 99%

An efficient three-dimensional rhizosphere modeling capability to study the effect of root system architecture on soil water and reactive transport

et al. 2019

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Aims The objective of this research was to develop a three-dimensional (3D) rhizosphere modeling capability for plant-soil interactions by integrating plant biophysics, water and ion uptake and release from individual roots, variably saturated flow, and multicomponent reactive transport in soil. Methods We combined open source software for simulating plant and soil interactions with parallel computing technology to address highly-resolved root system architecture (RSA) and coupled hydrobiogeochemical processes in soil. The new simulation capability was demonstrated on a model grass, Brachypodium distachyon. Results In our simulation, the availability of water and nutrients for root uptake is controlled by the interplay between 1) transpiration-driven cycles of water uptake, root zone saturation and desaturation; 2) hydraulic redistribution; 3) multicomponent competitive ion exchange; 4) buildup of ions not taken up during kinetic nutrient uptake; and 5) advection, dispersion, and diffusion of ions in the soil. The uptake of water and ions by individual roots leads to dynamic, local gradients in ion concentrations. Conclusion By integrating the processes that control the fluxes of water and nutrients in the rhizosphere, the modeling capability we developed will enable exploration of alternative RSAs and function to advance the understanding of the coupled hydro-biogeochemical processes within the rhizosphere.

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A soil-plant-atmosphere continuum (SPAC) model for simulating tree transpiration with a soil multi-compartment solution

Cited by 32 publications

References 52 publications

Remote sensing of forest gas exchange: Considerations derived from a tomographic perspective

Remote sensing of forest gas exchange: Considerations derived from a tomographic perspective

Xylem–phloem hydraulic coupling explains multiple osmoregulatory responses to salt stress

An efficient three-dimensional rhizosphere modeling capability to study the effect of root system architecture on soil water and reactive transport

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