Abstract
AimsThe 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.MethodsWe 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.ResultsIn 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.ConclusionBy 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.
Highlights
The rhizosphere is a complex interaction zone for hydrological and biogeochemical processes characterized by large gradients in chemical and biological concentrations and physical properties along the root-soil interface (Helliwell et al 2017)
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 Root system architecture (RSA) and function to advance the understanding of the coupled hydro-biogeochemical processes within the rhizosphere
To simulate the root and soil interactions, three open source software tools were used: 1) RootBox (Leitner et al 2010a, 2010b; Schnepf et al 2018), a 3D dynamic Lindenmayer System (L-systems) model of RSA, to generate the root system geometry constrained by B. distachyon root attributes reported in the literature; 2) BioCro (Jaiswal et al 2017; Wang et al 2015), a process-based plant biophysics model for simulating energy crops, to calculate the transpiration rates that drive the coupled root and soil water flow simulation; and 3) eSTOMP (Yabusaki et al 2011), a variably saturated flow and multicomponent reactive transport simulator, to model the coupled process interactions given the root system geometry and boundary conditions
Summary
The rhizosphere is a complex interaction zone for hydrological and biogeochemical processes characterized by large gradients in chemical and biological concentrations and physical properties along the root-soil interface (Helliwell et al 2017). Root system and rhizosphere processes govern ecosystem plant water and nutrient use efficiency. Representations of these processes in numerical models are critical because they profoundly impact global carbon stocks and vegetation feedbacks (Finzi et al 2015). The term “multicomponent reactive transport” is taken to mean that multiple reactions can share the same ion This can lead to interactions between ions and competition for common ions that systematically control concentrations. Changes in the pH or the aqueous concentration of an individual exchangeable cation systematically affects the concentration of all exchangeable cations (Chung and Zasoski 1994) This differs from some nutrient uptake models which may have multiple nutrients, but without interactions
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