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Sustainable biomaterials such as natural fibers and biochars have been increasingly used in green infrastructures such as landfill covers for its dual-advantages of climate change mitigation and waste management. The existing studies did not systematically discuss the comparison on how biochar (stable carbon) and fiber (likely degradable), influence plant growth and water retention abilities in unsaturated soils. Also, the effect of photochemistry in the amended soils has rarely been investigated. This study addresses the limitations of previous investigations by exploring plant parameters such as photochemical yield, stomatal conductance, root area index, and unsaturated soil hydraulic parameters, including soil water retention curves (SWRC) of amended soils. Pot experiments were conducted in an environmentally controlled greenhouse. Two biochars from different plant-based feedstocks (Eichhornia crassipes, Prosopis juliflora) and one natural fiber (coir pith fiber) were mixed with soil at 5% and 10% application rate (by weight). Grass species of Axonopus compressus was planted to study the effects of different amendment materials and its corresponding plant responses during an applied drought period. The test results show that biochar amended soils increased the shoot growth by up to 100−200%. The stomatal conductance of the grass leaves increased by 54%−101% during the drought period for both biochars and coir amended soil. Furthermore, at low suction, the coir had a high water retention capacity than the biochars, explaining the observed higher stomatal conductance values. Importantly, it was discovered that the plant photochemical quantum yield responses associated with plant wilting was found to vary between 1500 and 1800 kPa for all the soil treatments. The study concludes with a newly developed mathematical expression based on the measurements of plant parameters and soil suction. The new equation could be used to optimize the irrigation frequency in order to

Aims: We investigated and compared the variability in biomechanical properties of Chrysopogon zizanioides L. (vetiver grass), including tensile strength, Young's modulus, and breakage strain, which have direct implication to root reinforcement to slope. Methods: We tested the effects of growth condition (pots versus field), root water content (hydrated versus oven dried), and loading speed (16 mm/min versus 200 mm/min) on the biomechanical properties of vetiver roots (n = 344) via a series of uniaxial tensile tests. We also measured the root biomechanical traits such as diameter, density, degree of saturation, and relative root dry weight. Results: Although the strength and modulus followed a negative power law relationship with root diameter (R2 up to 0.69), the strain–diameter relationship was linear (R2 = 0.20). Growth condition and loading speed did not have significant effects on the root biomechanical properties, whereas root water content showed significant effects on these properties, particularly in fine roots (<0.9 mm). Dried roots had higher strength and modulus but smaller strain than hydrated roots. Conclusion: A major source of the variability in strength, modulus, and strain of vetiver roots was root water content, which occurred primarily in fine roots (<0.9 mm). Considering slope stability, testing hydrated roots would give a lower estimate of strength than the case of dried roots, but it might overestimate root ductility and underestimate the time-of-slope failure. © 2021 Elsevier B.V.

Plant roots affect soil water regime through root-water uptake upon transpiration. This process induces soil matric suction, which affects soil hydraulic conductivity, soil shear strength and hence shallow soil stability. This is referred to as plant hydrological reinforcement in the soil bioengineering application. Recent experimental evidence put forward by the authors has demonstrated that plant hydrological reinforcement should not be exclusively limited to the effects of root-water uptake and plant transpiration. The presentation will provide some new evidence of other potential aspects of plant hydrological reinforcement, namely (1) root-induced changes in soil hydraulic properties, (2) root water-dependent bio-hydro-mechanical properties. In aspect (1), laboratory test results on how root growth dynamic alter the soil pore size distribution and hence affect both the soil water retention curve and hydraulic conductivity will be presented. To highlight the effects of these root-induced changes in soil properties on slope water regime and slope stability, numerical simulation employing a dual-permeability water transport model in unsaturated rooted soil will be discussed. In aspect (2), a new concept, hysteretic root water retention curve (relationship between root water content and root water potential), will be introduced with support of some preliminary data. How root water retention affects the root biomechanical properties including not only tensile strength and Young’s modulus that have received wide attention in the soil bioengineering literature but also breakage strain will be presented. New data will be provided in order to attempt to use root water content to explain the large variability of biomechanical properties observed in the literature.