Xi Sun

Expansive clays present significant geotechnical challenges, often damaging structures and road networks, and requiring reliable stabilization techniques. This study investigates the combin... Practical ApplicationsExpansive clays pose serious risks to transport infrastructure and buildings, often requiring costly remediation. Stabilization of such soils is therefore essential. However, ...

The soil–water retention curve (SWRC) is a fundamental property that governs the hydraulic and mechanical behavior of unsaturated soils. Laboratory SWRC determination remains time-consuming and costly, promoting indirect estimation methods. However, existing methods often oversimplify the pore structure and particle arrangement of soils and neglect the effect of capillary menisci, resulting in discrepancies from natural soil behavior. This study proposes a novel method to estimate the SWRC of coarse-grained soils based on grain size distribution (GSD) and relative density. In the proposed method, soil particles are idealized as spheres in a two-dimensional (2D) plane, and the packing structure is modeled using representative quadrilaterals composed of four poly-disperse particles. The GSD is employed to calculate the probability of different particle sizes occupying the corners of the quadrilateral elements, while the relative density defines their geometric configuration. The water retention behavior is then evaluated using the geometric relationships between the air–water interface and particle radii. The predicted SWRCs are in good agreement with experimental data, indicating that the method can effectively capture the water retention characteristics of coarse-grained soils governed by capillary effects. The method’s applicability is limited to coarse-grained soils and excludes clayey soils where adsorbed water dominates retention mechanisms.

Aims: This study evaluates the water use strategies and physiological resilience of three Australian native tree species in saline soils to assess their potential for phytoremediation under climate change. We hypothesise that species with high water demand and delayed stomatal closure under aridity can enhance soil salinity mitigation through sustained transpiration and groundwater regulation. Methods: Continuous sap flow measurements were recorded over 12 months on nine trees (three per species) from three species across three moderately saline sites in Melbourne, Australia. Detailed analyses of morphological traits, sapwood properties, and soil profiles (including texture and water content) were conducted. Diurnal sap flow patterns, peak flow timing, and physiological responses to temperature and vapour pressure deficit (VPD) were evaluated to determine species-specific thresholds for heat and drought tolerance. Results: Melaleuca styphelioides exhibited the highest water use, consuming 128% and 97% more water monthly than Lophostemon confertus and Corymbia maculata , respectively. Its peak sap flow occurred later in the day (15:00–17:00), coinciding with sustained stomatal conductance under high VPD (1.9–2.0 kPa) and extreme temperatures (41 °C). Optimal physiological performance for this species occurred at higher temperatures (32.2–33.4 °C) and VPD (1.9–2.0 kPa). Conclusions: Melaleuca styphelioides may warrant further investigation as a potential candidate for water management in saline environments, given its higher water consumption and ability to maintain sap flow under elevated temperature and VPD conditions. These findings suggest that additional research, incorporating larger sample sizes and direct measurements of soil salinity changes, would be valuable to evaluate the suitability of this species for phytoremediation applications in aridifying regions.

Aims: This study investigates the complex interactions between urban trees and expansive clay soils, focusing on two prevalent species (Corymbia maculata and Lophostemon confertus) in Melbourne’s urban landscape. Limited field data and understanding of species-specific water use necessitate this research. We aim to quantify the spatiotemporal variability in soil-plant-water interactions within the urban contexts, a crucial factor for informed green infrastructure planning and sustainable ecosystem management in metropolitan areas. Methods: Comprehensive field measurements were conducted over 12 months, including soil movement, soil water dynamics, tree transpiration, and leaf water potential. Sap flow sensors monitored tree water requirements. Laboratory soil testing determined soil properties and developed soil suction and water content profiles. The intercorrelation between soil water dynamics and tree water use was investigated. Results: Peak water use for both trees occurred during summer, contributing 32–40% of their total consumption. C. maculata transpired 48.1 kL, exceeding L. confertus by 106%. The trees’ desiccation influence extended horizontally to 0.4–0.5 times the tree height and vertically to 2.3–3.3 m depth. Soil water content explained 31–36% of soil movement variability, with a strong correlation (R² > 0.9) between soil suction and water content within the active root zone. Conclusions: This study enhances our mechanistic understanding of urban tree-soil interactions, providing valuable insights for sustainable city planning. It emphasizes species-specific considerations in tree selection and placement, especially in areas with expansive soils. The robust field data contributes to refining predictive models of soil-plant-atmosphere interactions in urban landscapes, supporting informed decision-making in urban greening initiatives.