Purpose: Simultaneously interacting rhizosphere processes determine emergent plant behaviour, including growth, transpiration, nutrient uptake, soil carbon storage and transformation by microorganisms. However, these processes occur on multiple scales, challenging modelling of rhizosphere and plant behaviour. Current advances in modelling and experimental methods open the path to unravel the importance and interconnectedness of those processes across scales. Methods: We present a series of case studies 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. Results: Each case study includes a model that links scales and experimental data to explain and predict spatial and temporal distribution of rhizosphere components. We exemplify the state-of-the-art modelling tools in this field: image-based modelling, pore-scale modelling, continuum scale modelling, and functional-structural plant modelling. We 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. Furthermore, we demonstrate ways of modelling the links between rhizodeposition and plant nutrient uptake or soil microbial activity. Conclusion: Modelling allows to integrate new experimental data across different rhizosphere processes and scales and to explore more variables than is possible with experiments. 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 including the dynamics of root growth is the logical next step for future research.

Aims: High viscosity, low surface tension and hydrophobicity are specific properties of maize root mucilage which contribute to modulate the spatial configuration of the liquid phase in soil pores. Several processes in the rhizosphere, in particularly nutrient absorption, root exudation and microbial activity, may cause strong temporal variations in the chemistry of the soil solution of the rhizosphere. Although the physical properties of maize root mucilage have been repeatedly measured in the last years, their variation upon a changing chemical environment and understanding of the chemical mechanisms governing these properties remain unexplored.Methods: We investigated how flow and surface properties of maize root mucilage varied by changes in pH, calcium chloride (CaCl₂) and lecithin concentrations.Results: The physical properties of mucilage can strongly vary depending on the environmental conditions. Low surface tension of maize root mucilage at pH7 was increased by addition of calcium. Upon pH change and lecithin addition, hydrophobic mucilage turned hydrophilic. High Ca concentration above 0.83 mmol Ca (g dry mucilage)⁻¹, the addition of 167 μg lecithin (g dry mucilage)⁻¹and a pH rise to 9 decreased the viscosity of mucilage.Conclusion: Such variations strongly suggest that the role of mucilage in hydraulic processes in the rhizosphere depends on changes of solutes concentration and composition, which themselves vary according to plant growth and soil water content. It seems that mucilage can best serve as a hydraulic bridge only under certain chemical environments, whose spatio-temporal occurrence in the changing rhizosphere remains to be defined.

This study aimed to evaluate changes in abundance, structure, and enzyme activity of the soil microbiome in response to 4 years of mulching using either black polyethylene plastic film (PM) or wheat straw (SM). Soil samples (depth 0–5 and 5–10 cm) were collected from conventional strawberry plots, in two samplings: 1 week prior (S1) and 7 weeks after straw application (S2). Selected soil properties were monitored in each system and the abundance and structure of microbial communities were characterized via phospholipid fatty acid (PLFA) analysis. The investigation of soil microbial functions included activities of the enzymes chitinase, leucine aminopeptidase, and acid phosphatase, as well as function genes involved in nitrogen transformation. Each mulch system resulted in distinct physicochemical properties. In particular, a pH value higher by one-unit under PM (7.6 ± 0.3) compared to SM (6.5 ± 0.3) was observed. Values for SOC, DOC, and total-N were 15%, 22%, and 16% higher in PM than in SM. The microbial biomass (total PLFAs) was 1.5-fold higher in SM compared to PM. The abundance of soil fungi (F) and bacteria (B) increased by 37% and 44% after straw incorporation compared to PM (S2). In particular, Gram-negative bacteria (gr–) increased by twofold in SM. Consequently, wider F:B and gr+:gr– ratios were observed in PM. According to the shifts in microbial abundance, the activity of the enzyme chitinase was lower by 27% in PM, while the activity of the acid phosphatase increased by 32%. Denitrification genes were not affected by the mulching systems. In conclusion, the abundance and structure of the investigated microbial groups and the enzyme activities were strongly influenced by the mulching system. In detail, effects on microbiota were primarily attributed to the altered soil pH and probably the input of degradable organic matter with straw mulching in SM. This resulted in higher abundance of soil microorganisms in SM, although measures within this cultivation system such as fungicide application may have exerted adverse effects on the microbiota.

An increasing amount of TiO2 engineered nanoparticles (TNP) is released into soils and sediments, increasing the need for dedicated detection methods. Titanium is naturally present in soils at concentrations typically much higher than the estimated concentrations for TNP. Therefore, a precise knowledge of this natural background, including the colloidal fraction, is required for developing adapted strategies for detecting TNP. In this study, we characterized the natural colloidal Ti-background by analyzing eight soils with different properties and origins. A combination of X-ray fluorescence analysis and ICP-OES was used for determining the silicate bound fraction, which was a minor fraction for all soils (0–32%). The colloidal fraction obtained by extracting colloids from soil prior to ICP-OES measurements ranged between 0.3% and 7%. Electron microscopy and hydrodynamic chromatography confirmed that Ti in the form of colloids or larger particles was mostly present as TiO2 minerals with a fraction smaller than 100 nm. The size distribution mode of the extracted colloids determined using hydrodynamic chromatography ranged between 80 and 120 nm. The chromatograms suggested a broad size distribution with a significant portion below 100 nm. In addition to these data, we also discuss possible implications of our findings for the method development for detecting TNP in soils.