Linking rhizosphere processes across scales: Opinion

Abstract

PurposeSimultaneously interacting small-scale rhizosphere processes determine emergent plant-scale behaviour, including growth, transpiration, nutrient uptake, soil carbon storage and transformation by microorganisms. Current advances in modelling and experimental methods open the path to unravel and link those processes.MethodsWe present a series of examples of state-of-the art simulations addressing this multi-scale, multi-process problem from a modelling point of view, as well as from the point of view of integrating newly available rhizosphere data and images.ResultsEach example includes a model that links scales and experimental data to set-up simulations that explain and predict spatial and temporal distribution of rhizodeposition as driven by root architecture development, soil structure, presence of root hairs, soil water content and distribution of soil water. Furthermore, two models explicitly simulate the impact of the rhizodeposits on plant nutrient uptake and soil microbial activity, respectively. This exemplifies the currently available state of the art modelling tools in this field: image-based modelling, pore-scale modelling, continuum scale modelling and functional-structural plant modelling. We further show how to link the pore scale to the continuum scale by homogenisation or by deriving effective physical parameters like viscosity from nano-scale chemical properties.ConclusionModelling allows to integrate and make use of new experimental data across different rhizosphere processes (and thus across different disciplines) and scales. Described models are tools to test hypotheses and consequently improve our mechanistic understanding of how rhizosphere processes impact plant-scale behaviour. Linking multiple scales and processes is the logical next step for future research.

Carbon allocation to root exudates is maintained in mature temperate tree species under drought

“…Although the opposite has also been shown (Ruehr et al ., 2009), these studies mostly measured C allocation as root growth or exudation at the root‐branch level but did not assess whether C exudation at the root‐system and tree levels also increased. Extending root C exudation to larger scales helps to identify processes related to the up‐ and downregulation of exudation at the whole‐tree level and the linkage to rhizosphere characteristics (Prescott et al ., 2020; Schnepf et al ., 2022). Given the potential ecological benefits of belowground C allocation in the forest´s capacity to recover from drought (Hagedorn et al ., 2016) and for tree drought tolerance (Carminati et al ., 2016), we hypothesized that trees would increase the partitioning of C from net photosynthesis into root exudation under drought.…”

Understanding the joint impacts of soil architecture and microbial dynamics on soil functions: Insights derived from microscale models

“…However, the rhizosphere constitutes hotspots of soil microbial activity and rhizodeposition has a role in the priming effect and soil aggregation (e.g., Baumert et al, 2018). Current advances in modelling and experimental methods offer new opportunities to quantify the rhizosphere at microscopic scales and advance new insights into how these microscopic processes impact across scales, and current challenges in the rhizosphere (Schnepf et al, 2022). Microscale models could help in quantifying the respective role of detritusphere and rhizosphere in SOM decomposition and greenhouse gas production.…”

Soil water status shapes nutrient cycling in agroecosystems from micrometer to landscape scales

“…In addition to the focus on individual rhizosphere compounds, it is important to consider the interplay between multitudes of processes taking place in the rhizosphere at various spatial and temporal scales (Schnepf et al., 2022). For instance, plants can alter their rhizosphere by releasing organic substances that affect the hydraulic and/or chemical nature of the soil surrounding them.…”