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Murviel-lès-Montpellier, France

Ghestem M.,AgroParis Technology | Veylon G.,IRSTEA | Bernard A.,IRSTEA | Vanel Q.,EPHE Paris | Stokes A.,French National Institute for Agricultural Research
Plant and Soil | Year: 2014

Background and aims: Vegetation can be used to stabilise slopes with regard to shallow landslides, but the optimal plant architecture for conferring resistance is not known. This study aims at identifying root morphological traits which confer the most resistance to soil during shearing. Methods: Three species used for slope stabilisation (Ricinus communis L., Jatropha curcas L. and Rhus chinensis Mill.) were grown for 10 months in large shear boxes filled with silty clay similar to that found in Yunnan, China. Direct shear tests were then performed and compared to fallow soil. Root systems were excavated and a large number of traits measured. Results: Shear strength and deformation energy were enhanced by the presence of roots. Regardless of confining pressure, R. communis conferred most resistance due to its taprooted system with many vertical roots. J. curcas possessed oblique and vertical roots which created fragile zones throughout the soil profile. The least efficient root system was R. chinensis which possessed many horizontal lateral roots. Soil mechanical properties were most influenced by (i) density of roots crossing the shear plane, (ii) branching density throughout the soil profile, (iii) total length of coarse roots above the shear plane and (iv) total volume of coarse roots and fine root density below the shear plane. During failure, fine, short and branched roots slipped through soil rather than breaking. Conclusion: Root morphological traits such as density, branching, length, volume, inclination and orientation influence significantly soil mechanical properties. © 2013 Springer Science+Business Media Dordrecht. Source

Mickovski S.B.,Jacobs Engineering | Stokes A.,French National Institute for Agricultural Research | van Beek R.,University Utrecht | Ghestem M.,AgroParis Technology | Fourcaud T.,CIRAD - Agricultural Research for Development
Ecological Engineering | Year: 2011

The finite element (FE) method has been used in recent years to simulate overturning processes in trees and to better comprehend plant anchorage mechanics. We aimed at understanding the fundamental mechanisms of root-soil reinforcement by simulating direct shear of rooted and non-rooted soil. Two- (2D) and three-dimensional (3D) FE simulations of direct shear box tests were carried out using readily available software for routine strength assessment of the root-soil composite. Both rooted and non-rooted blocks of soil were modelled using a simplified model of root distribution and root material properties representative of real roots. Linear elastic behaviour was assumed for roots and the soil was modelled as an ideally plastic medium. FE analysis showed that direct shear tests were dependent on the material properties specified for both the soil and roots. 2D and 3D simulations of direct shear of non-rooted soil produced similar results and any differences between 2D and 3D simulations could be explained with regard to the spatial complexity of roots used in the root distribution model. The application of FE methods was verified through direct shear tests on soil with analogue roots and the results compared to in situ tests on rooted soil in field conditions. © 2011 Elsevier B.V. Source

Magnetic susceptibility can be used for assessing anthropogenic pollution in solid matrices, including soils and composts. This work studies the distribution of trace elements and magnetic susceptibility in the different size fractions of six composts, for the development of measures aimed at reducing compost pollution at the production stage. The results showed that magnetic susceptibility decreased with increasing particle size in all composts, and the same was true for most trace element concentrations. Magnetic susceptibility was significantly correlated with Fe, as well as with Cu, Zn, Pb, Cr and Ni, which proves the relationship between the presence of ferric particles and trace element contamination in compost. Our results suggest that the association of trace elements and magnetic susceptibility is a characteristic feature in municipal solid waste composts. © 2014, Universia. All rights reserved. Source

Ghestem M.,AgroParis Technology | Cao K.,CAS Xishuangbanna Tropical Botanical Garden | Cao K.,Guangxi University | Ma W.,CAS Kunming Institute of Botany | And 4 more authors.
PLoS ONE | Year: 2014

Major reforestation programs have been initiated on hillsides prone to erosion and landslides in China, but no framework exists to guide managers in the choice of plant species. We developed such a framework based on the suitability of given plant traits for fixing soil on steep slopes in western Yunnan, China. We examined the utility of 55 native and exotic species with regard to the services they provided. We then chose nine species differing in life form. Plant root system architecture, root mechanical and physiological traits were then measured at two adjacent field sites. One site was highly unstable, with severe soil slippage and erosion. The second site had been replanted 8 years previously and appeared to be physically stable. How root traits differed between sites, season, depth in soil and distance from the plant stem were determined. Root system morphology was analysed by considering architectural traits (root angle, depth, diameter and volume) both up- and downslope. Significant differences between all factors were found, depending on species. We estimated the most useful architectural and mechanical traits for physically fixing soil in place. We then combined these results with those concerning root physiological traits, which were used as a proxy for root metabolic activity. Scores were assigned to each species based on traits. No one species possessed a suite of highly desirable traits, therefore mixtures of species should be used on vulnerable slopes. We also propose a conceptual model describing how to position plants on an unstable site, based on root system traits. © 2014 Ghestem et al. Source

Chelle M.,French National Institute for Agricultural Research | Liu S.,AgroParis Technology | Mathieu A.,AgroParis Technology | Ney B.,AgroParis Technology
Plant Growth Modeling, Simulation, Visualization and Applications, Proceedings - PMA09 | Year: 2010

Function-Structure Plant models (FSPM) seem attractive to better understand the complex interactions between plant growth, canopy morphogenesis, and epidemics. Epidemics are driven by climate factors and among them, temperature is known to play a major role. Thus, weather station measurement is commonly used to drive epidemics models. However, the relationship between climate and within-canopy microclimate is mainly affected by the canopy architecture. Thus, the general question addressed in this study is: where air temperature should be measured as input of FSPM for sick plants? © 2010 IEEE. Source

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