No description available.

Thesis (M. Sc.(Agronomy)) -- University of Limpopo, 2015 / Cowpea (Vigna unguiculata L. Walp) is an important grain legume grown in many parts of the world mostly by smallholder (SH) farmers. Low soil phosphorus (P) and drought stress are major constraints to legume production and threaten food security. Root architecture is a spatial configuration of the root system which is influenced by moisture status and P uptake. A field experiment was conducted at Ukulima farm near Modimolle in Waterberg district during 2012/13 summer growing season. The treatments comprised of two levels each for soil P (low and high) and moisture status (water stress and well-watered); and eight cowpea genotypes (Tvu 4632, Tvu 6365, Tvu 9848, Tvu 15445, Tvu 16408, Tvu 15143, Oloyin and IT00K-1217). The low P level implied the available P in the soil measured in situ, which was less than 8 mg kg-1 while the high P level entailed fertilization at the rate of 40 kg P ha-1 application to achieve approximately 35 mg P kg-1 of soil . The root traits measured included angle of adventitious and basal roots, number of basal roots, tap root diameters at 5, 10, 15 and 20 cm soil depths; lateral branching densities at depth 5,10 and 15 cm, nodule score, deep score, shallowness score, 3rd order branching density, and 1.5 branching densities at 5 and 10 cm depth. Plant parameters measured were plant height, number of pods per plant, number of seeds per pod, length of the pods, unshelled weight, shelled weight and number of primary and secondary branches. Photosynthetic parameters measured were photosynthetic rate, intercellular CO2 concentration, water conductance, transpiration rate, vapour pressure deficits, sample cell CO2, sample cell H2O and relative humidity in the cell. All treatment factors were combined as split-split plot arrangement fitted into randomized complete block design; with four replicates. Results indicate that the lateral root branching density at 5 and 10 cm differed significantly (P≤0.05) across cowpea genotypes. Genotype showed significant effect on taproot diameter at 10 cm. Moisture status and P level exerted significant effect on cowpea genotypes 15 cm. There were significant differences (P≤0.05) for lateral root branching density observed at 5 and 10 cm depth in P rates x genotype interaction. Statistical analysis showed that P levels and cowpea genotypes had significant effects (P≤0.05) on mean plant height, biomass and highly significantly effects (P≤0.01) on number of branches, days to physiological maturity and mean pod length. The interaction between cowpea genotype and moisture stress condition significantly (P≤0.05) affected hundred (100) seed weight. Cowpea genotype Tvu16408 obtained highest grain yield of 3240 kg ha-1 and lowest was by IT00K1217 which obtained grain yield of 1256 kg ha-1. Results showed that photosynthetic rate, water conductance, transpiration rate, sample cell CO2, sample cell H2O, relative humidity in the cell, intercellular CO2 and vapour pressure deficit differed significantly (P≤0.05) across cowpea genotypes. Soil moisture condition and cowpea genotype exerted significant (P≤0.01) effect on photosynthetic rate, water conductance, transpiration rate, sample cell CO2, sample cell H2O and relative humidity in the cell. Variation in P levels had no significant effect on the measured photosynthetic parameters. Oloyin genotype had the highest photosynthetic rate followed by Tvu 4632 while cowpea genotype Tvu 9848 had the least photosynthetic rate. Interaction of moisture stress and cowpea genotype had a significant effect on intercellular CO2 concentration. Water stress reduced the intercellular CO2 concentration of Oloyin, Tvu 6365 and 4632 but resulted in a significant increase in intercellular CO2 concentration in Tvu 9848 genotype. Results showed that variation in soil P level exerted a significant (P≤0.05) effect on grain tissue P content and uptake, and a highly significant (P≤0.01) difference in P content across the various cowpea genotypes. Moisture stress exerted a significant (P≤0.05) difference on P uptake. The results showed that P levels and cowpea genotype variation exerted significant (P≤0.05) effects on P content, P uptake and nitrogen (N) uptake. Moisture status and cowpea genotype variation exerted significant (P≤0.05) effects on total N and N uptake. Cowpea genotype Tvu 9848 obtained more total N content (4.37%), while the lowest total N content was obtained by cowpea genotype Tvu 15445 with 3035 mg kg-1. The interaction between cowpea genotype and moisture status exerted a significant (P≤0.05) effect on N and P uptake of immature green pods harvested. There is a need to conduct more studies to identify cowpea genotypes, their root architecture and agronomic measures that can do well under xvii drought stress and low soil P conditions. Research needs to be conducted to enhance cowpea productivity under both low soil P and drought stress. Keywords: cowpea genotypes; moisture stress; phosphorus fertilisation; root traits

No description available.

Forests account for a large portion of global carbon storage. Almost half of this carbon is stored underground. Roots, especially fine-roots (diameter ≤ 2 mm) are an important part of soil carbon, and play a number of ecological roles. Yet, the below-ground parts of trees are still poorly understood. The aim of this report was to understand environmental controls over plants traits. I tested if plants shift their root traits towards a resource conservative strategy when environmental conditions are challenging (dry and cold). Furthermore, the contribution of different fine-root diameters to total root length (TRL), surface area (SA) and root volume (VO) was assessed. Root traits such as TRL, SA, VO, fine-root diameter, specific root length (SRL) and root tissue density (RTD) were quantified. The root samples are taken from 11 old growth Swedish forests across a climate gradient in three different soil moisture categories per forest (dry, intermediate, wet). Fine-roots were scanned, and analysed with the RhizoVision Explorer Software (Version 2.0.3). Uni-factorial ANOVAs, combined with Tukey’s posthoc test, or linear regressions were conducted, and the results revealed no significant effects of the summer air temperature on root traits. However, higher soil moisture was found to decrease RTD, but increase fine-root diameters significantly. These findings did not confirm the plants aim on building resource conservative root traits in challenging conditions. Instead, they highlighted variability among and within forests suggest that multiple factors influence root morphology and function. This study contributes to our understanding of how fine-roots respond to environmental conditions.

No description available.

Drought is the major environmental factor affecting crop growth, yield and quality. Two experiments were conducted to understand rice genotypic variability responses to drought stress conditions during seed germination and early-seedling growth. In Experiment I, the influence of wide range of osmotic stress on seed germination properties of 15 rice cultivars were studied using polyethylene glycol media. In Experiment II, seedling morph-physiological parameters including root traits were quantified by subjecting rice seedlings to three different soil moisture treatments, 100, 66 and 33% field capacity. Rice cultivars differed in their response to drought at both the stages. Cultivars were classified into different drought tolerant groups based cumulative drought response indices. Based on seed- and early-season growth and developmental responses, RU1104122, Rex, CL111 and RU1304154 were identified as drought tolerant among the rice cultivars tested. The identified tolerant cultivars will be a source for rice breeders to develop new drought tolerant cultivars.

Enquanto em regiões temperadas o conhecimento sobre a relação solo-vegetação é consolidado, nos trópicos e subtrópicos é preliminar. É urgente a necessidade de se determinar os fatores abióticos que controlam padrões vegetacionais visando dar suporte a estudos de recuperação e conservação. O presente estudo analisa a relação entre fatores abióticos e vegetação campestre na forma de três artigos científicos (capítulos I, II e III) e um artigo de revisão (capítulo IV). Nos primeiros três artigos, analisou-se a variância da vegetação em diferentes escalas ecológicas; e no artigo de revisão, discutiu-se de forma aplicada a variância de fatores bióticos e abióticos em resposta à degradação. Dessa forma, a presente tese objetivou responder as seguintes questões: (I) Que diferenças podem ser observadas dentro de uma mesma espécie quanto à funcionalidade e suas estratégias de alocação sob diferentes graus de disponibilidade de recursos?; (II) Quão variáveis são as propriedades físicas e químicas do solo em diferentes escalas espaciais; e existem propriedades dos solos que podem explicar com maior precisão a distribuição das espécies em diferentes escalas espaciais? (III) Que porcentagem de variância da vegetação pode ser explicada por propriedades pedológicas e climáticas; e quais características de solo e clima melhor explicam esses padrões de vegetação? No capítulo IV é apresentado um modelo conceitual sobre degradação dos campos e sua aplicação aos campos do Rio Grande do Sul (RS). Para responder as questões acima usei dados ao nível de espécie de campos calcáreos da Alemanha (capítulo I); dados ao nível de comunidade em seis áreas campestres do Rio Grande do Sul, sul do Brasil (capítulos II e III); e através da revisão de literatura relacionada à degradação, quanto à capacidade de recuperação dos campos do RS (capítulo IV). Os resultados evidenciaram que: (I) dentro de espécies ficaram evidentes duas estratégias frente à limitação de recursos, enquanto a resposta dos atributos aos diferentes tratamentos se mostrou constante; (II) a variação dos parâmetros do solo relaciona-se à escala espacial aplicada e a variância da vegetação geralmente responde a diferentes parâmetros de solo em diferentes escalas; (III) 45% da variância da vegetação entre biomas nos campos do RS foi explicada por características pedológicas e climáticas, sendo em grande parte governada pela precipitação anual e a porcentagem de saturação por alumínio do solo; e (IV) o modelo conceitual apresenta variações ao longo de dois eixos (biótico e abiótico) e poderá servir de suporte a estudos de conservação e recuperação de campos tropicais e suptropicais, bem como facilitar a tomada de decisões quanto ao manejo e conservação. Como conclusão geral, verificou-se que a vegetação campestre responde a variações ambientais em diferentes escalas espaciais e pode adotar diferentes estratégias para sobrepor filtros ambientais e processos de degradação. O entendimento da relação entre a vegetação e o meio abiótico é de grande importância para tomada de decisões quanto ao emprego de formas alternativas de manejo e conservação. / Whereas in temperate regions the abiotic-biotic relationship is well-known, in the tropics and subtropics our understanding is still preliminary. There is an urgent need to determine abiotic factors that control vegetation patterns in order to give support to restoration and conservation approaches. The present thesis analyses the relationship between abiotic factors and grassland vegetation in three original research papers (chapters I, II and III) and a review paper (chapter IV). In the first three papers, vegetation variance in response to abiotic factors was analyzed at different ecological scales; and in the fourth, the variance in biotic and abiotic factors in response to degradation process was discussed with a more applied view. Thus in this thesis the aim is to answer the following questions: (I) Which differences can be found in functional plant traits and allocation strategies within species at different levels of water and nutrient availability?; (II) How variable are physical and chemical parameters in different spatial scales; and are there soil parameters that can more accurately explain plant distribution in different spatial scales? (III) How much of RS grassland vegetation variance can be explained by soil and climatic properties; and which climatic and soil properties better explain these vegetation patterns? In chapter IV a conceptual model of grassland degradation is presented and applied to Rio Grande do Sul (RS) grasslands. To address these questions I used species-level data in a calcareous grassland in Germany (chapter I); community-level data in six sites in RS, South Brazilian grasslands (chapter II and III); and a review of literature studies concerning RS grassland degradation and restorability (chapter IV). The results showed that: (I) at a intraspecific level, the study species showed two allocation strategies in relation to resource stress, while the responses of individual traits to the soil treatments were consistent across species; (II) soil parameters variation are related to the measurement scale applied and the vegetation variance often responds to different soil parameters at different scales; (III) climatic and soil properties explained 45% of vegetation variance between biomes in RS grasslands and the main factors controlling its variance are annual precipitation and percent aluminum saturation; and (IV) the conceptual model is displayed as biotic and abiotic changes along the axes and can serve as a general framework to study degradation and restorability of tropical and subtropical grasslands, and further it may facilitate decisions on alternative management and conservation. As a general conclusion, the grassland vegetation responds to changes in the environment in different scales and may use different strategies to overcome environmental selective forces and degradation process. The understanding of this relationship is of high importance to facilitate decisions on alternative management and conservation.

Enquanto em regiões temperadas o conhecimento sobre a relação solo-vegetação é consolidado, nos trópicos e subtrópicos é preliminar. É urgente a necessidade de se determinar os fatores abióticos que controlam padrões vegetacionais visando dar suporte a estudos de recuperação e conservação. O presente estudo analisa a relação entre fatores abióticos e vegetação campestre na forma de três artigos científicos (capítulos I, II e III) e um artigo de revisão (capítulo IV). Nos primeiros três artigos, analisou-se a variância da vegetação em diferentes escalas ecológicas; e no artigo de revisão, discutiu-se de forma aplicada a variância de fatores bióticos e abióticos em resposta à degradação. Dessa forma, a presente tese objetivou responder as seguintes questões: (I) Que diferenças podem ser observadas dentro de uma mesma espécie quanto à funcionalidade e suas estratégias de alocação sob diferentes graus de disponibilidade de recursos?; (II) Quão variáveis são as propriedades físicas e químicas do solo em diferentes escalas espaciais; e existem propriedades dos solos que podem explicar com maior precisão a distribuição das espécies em diferentes escalas espaciais? (III) Que porcentagem de variância da vegetação pode ser explicada por propriedades pedológicas e climáticas; e quais características de solo e clima melhor explicam esses padrões de vegetação? No capítulo IV é apresentado um modelo conceitual sobre degradação dos campos e sua aplicação aos campos do Rio Grande do Sul (RS). Para responder as questões acima usei dados ao nível de espécie de campos calcáreos da Alemanha (capítulo I); dados ao nível de comunidade em seis áreas campestres do Rio Grande do Sul, sul do Brasil (capítulos II e III); e através da revisão de literatura relacionada à degradação, quanto à capacidade de recuperação dos campos do RS (capítulo IV). Os resultados evidenciaram que: (I) dentro de espécies ficaram evidentes duas estratégias frente à limitação de recursos, enquanto a resposta dos atributos aos diferentes tratamentos se mostrou constante; (II) a variação dos parâmetros do solo relaciona-se à escala espacial aplicada e a variância da vegetação geralmente responde a diferentes parâmetros de solo em diferentes escalas; (III) 45% da variância da vegetação entre biomas nos campos do RS foi explicada por características pedológicas e climáticas, sendo em grande parte governada pela precipitação anual e a porcentagem de saturação por alumínio do solo; e (IV) o modelo conceitual apresenta variações ao longo de dois eixos (biótico e abiótico) e poderá servir de suporte a estudos de conservação e recuperação de campos tropicais e suptropicais, bem como facilitar a tomada de decisões quanto ao manejo e conservação. Como conclusão geral, verificou-se que a vegetação campestre responde a variações ambientais em diferentes escalas espaciais e pode adotar diferentes estratégias para sobrepor filtros ambientais e processos de degradação. O entendimento da relação entre a vegetação e o meio abiótico é de grande importância para tomada de decisões quanto ao emprego de formas alternativas de manejo e conservação. / Whereas in temperate regions the abiotic-biotic relationship is well-known, in the tropics and subtropics our understanding is still preliminary. There is an urgent need to determine abiotic factors that control vegetation patterns in order to give support to restoration and conservation approaches. The present thesis analyses the relationship between abiotic factors and grassland vegetation in three original research papers (chapters I, II and III) and a review paper (chapter IV). In the first three papers, vegetation variance in response to abiotic factors was analyzed at different ecological scales; and in the fourth, the variance in biotic and abiotic factors in response to degradation process was discussed with a more applied view. Thus in this thesis the aim is to answer the following questions: (I) Which differences can be found in functional plant traits and allocation strategies within species at different levels of water and nutrient availability?; (II) How variable are physical and chemical parameters in different spatial scales; and are there soil parameters that can more accurately explain plant distribution in different spatial scales? (III) How much of RS grassland vegetation variance can be explained by soil and climatic properties; and which climatic and soil properties better explain these vegetation patterns? In chapter IV a conceptual model of grassland degradation is presented and applied to Rio Grande do Sul (RS) grasslands. To address these questions I used species-level data in a calcareous grassland in Germany (chapter I); community-level data in six sites in RS, South Brazilian grasslands (chapter II and III); and a review of literature studies concerning RS grassland degradation and restorability (chapter IV). The results showed that: (I) at a intraspecific level, the study species showed two allocation strategies in relation to resource stress, while the responses of individual traits to the soil treatments were consistent across species; (II) soil parameters variation are related to the measurement scale applied and the vegetation variance often responds to different soil parameters at different scales; (III) climatic and soil properties explained 45% of vegetation variance between biomes in RS grasslands and the main factors controlling its variance are annual precipitation and percent aluminum saturation; and (IV) the conceptual model is displayed as biotic and abiotic changes along the axes and can serve as a general framework to study degradation and restorability of tropical and subtropical grasslands, and further it may facilitate decisions on alternative management and conservation. As a general conclusion, the grassland vegetation responds to changes in the environment in different scales and may use different strategies to overcome environmental selective forces and degradation process. The understanding of this relationship is of high importance to facilitate decisions on alternative management and conservation.

Enquanto em regiões temperadas o conhecimento sobre a relação solo-vegetação é consolidado, nos trópicos e subtrópicos é preliminar. É urgente a necessidade de se determinar os fatores abióticos que controlam padrões vegetacionais visando dar suporte a estudos de recuperação e conservação. O presente estudo analisa a relação entre fatores abióticos e vegetação campestre na forma de três artigos científicos (capítulos I, II e III) e um artigo de revisão (capítulo IV). Nos primeiros três artigos, analisou-se a variância da vegetação em diferentes escalas ecológicas; e no artigo de revisão, discutiu-se de forma aplicada a variância de fatores bióticos e abióticos em resposta à degradação. Dessa forma, a presente tese objetivou responder as seguintes questões: (I) Que diferenças podem ser observadas dentro de uma mesma espécie quanto à funcionalidade e suas estratégias de alocação sob diferentes graus de disponibilidade de recursos?; (II) Quão variáveis são as propriedades físicas e químicas do solo em diferentes escalas espaciais; e existem propriedades dos solos que podem explicar com maior precisão a distribuição das espécies em diferentes escalas espaciais? (III) Que porcentagem de variância da vegetação pode ser explicada por propriedades pedológicas e climáticas; e quais características de solo e clima melhor explicam esses padrões de vegetação? No capítulo IV é apresentado um modelo conceitual sobre degradação dos campos e sua aplicação aos campos do Rio Grande do Sul (RS). Para responder as questões acima usei dados ao nível de espécie de campos calcáreos da Alemanha (capítulo I); dados ao nível de comunidade em seis áreas campestres do Rio Grande do Sul, sul do Brasil (capítulos II e III); e através da revisão de literatura relacionada à degradação, quanto à capacidade de recuperação dos campos do RS (capítulo IV). Os resultados evidenciaram que: (I) dentro de espécies ficaram evidentes duas estratégias frente à limitação de recursos, enquanto a resposta dos atributos aos diferentes tratamentos se mostrou constante; (II) a variação dos parâmetros do solo relaciona-se à escala espacial aplicada e a variância da vegetação geralmente responde a diferentes parâmetros de solo em diferentes escalas; (III) 45% da variância da vegetação entre biomas nos campos do RS foi explicada por características pedológicas e climáticas, sendo em grande parte governada pela precipitação anual e a porcentagem de saturação por alumínio do solo; e (IV) o modelo conceitual apresenta variações ao longo de dois eixos (biótico e abiótico) e poderá servir de suporte a estudos de conservação e recuperação de campos tropicais e suptropicais, bem como facilitar a tomada de decisões quanto ao manejo e conservação. Como conclusão geral, verificou-se que a vegetação campestre responde a variações ambientais em diferentes escalas espaciais e pode adotar diferentes estratégias para sobrepor filtros ambientais e processos de degradação. O entendimento da relação entre a vegetação e o meio abiótico é de grande importância para tomada de decisões quanto ao emprego de formas alternativas de manejo e conservação. / Whereas in temperate regions the abiotic-biotic relationship is well-known, in the tropics and subtropics our understanding is still preliminary. There is an urgent need to determine abiotic factors that control vegetation patterns in order to give support to restoration and conservation approaches. The present thesis analyses the relationship between abiotic factors and grassland vegetation in three original research papers (chapters I, II and III) and a review paper (chapter IV). In the first three papers, vegetation variance in response to abiotic factors was analyzed at different ecological scales; and in the fourth, the variance in biotic and abiotic factors in response to degradation process was discussed with a more applied view. Thus in this thesis the aim is to answer the following questions: (I) Which differences can be found in functional plant traits and allocation strategies within species at different levels of water and nutrient availability?; (II) How variable are physical and chemical parameters in different spatial scales; and are there soil parameters that can more accurately explain plant distribution in different spatial scales? (III) How much of RS grassland vegetation variance can be explained by soil and climatic properties; and which climatic and soil properties better explain these vegetation patterns? In chapter IV a conceptual model of grassland degradation is presented and applied to Rio Grande do Sul (RS) grasslands. To address these questions I used species-level data in a calcareous grassland in Germany (chapter I); community-level data in six sites in RS, South Brazilian grasslands (chapter II and III); and a review of literature studies concerning RS grassland degradation and restorability (chapter IV). The results showed that: (I) at a intraspecific level, the study species showed two allocation strategies in relation to resource stress, while the responses of individual traits to the soil treatments were consistent across species; (II) soil parameters variation are related to the measurement scale applied and the vegetation variance often responds to different soil parameters at different scales; (III) climatic and soil properties explained 45% of vegetation variance between biomes in RS grasslands and the main factors controlling its variance are annual precipitation and percent aluminum saturation; and (IV) the conceptual model is displayed as biotic and abiotic changes along the axes and can serve as a general framework to study degradation and restorability of tropical and subtropical grasslands, and further it may facilitate decisions on alternative management and conservation. As a general conclusion, the grassland vegetation responds to changes in the environment in different scales and may use different strategies to overcome environmental selective forces and degradation process. The understanding of this relationship is of high importance to facilitate decisions on alternative management and conservation.

La Chine est actuellement confrontée à de sérieux problèmes environnementaux et est listée parmi les pays qui contribuent le plus à la pollution et à la destruction de l'environnement mondial. En particulier, la Chine du Sud est une zone naturellement sujette aux glissements de terrain à cause de conditions tectoniques, climatiques et anthropiques particulièrement défavorables. Depuis la fin des années 1990, l'Etat chinois a mis en place des politiques de reforestation de grande envergure. mais il existe des lacunes de connaissances qu'il convient de combler. En particulier, le choix des espèces les plus adaptées n'est pas aisé parce que les processus par lesquels les plantes stabilisent les pentes ont besoin d'être mieux compris.En introduction, afin de mieux préciser les périmètres qui cadrent cette thèse, sont présentées la situation de la Chine du Sud au regard des glissements de terrain, la discipline d'éco-ingénierie et les solutions qu'elle peut apporter. Ainsi, ce travail (i) se concentre sur des espèces végétales locales, (ii) se limite aux glissements de terrain superficiels, et (iii) concerne à la fois les processus mécaniques et hydriques entre le sol et les racines. A l’intérieur de ces cadres, la thèse a pour objectif de répondre à la question scientifique : quels sont les propriétés racinaires qui influencent la stabilisation des pentes ? La réflexion est ensuite appliquée aux plantes de Chine du Sud afin d’identifier les meilleures espèces-outils. Pour répondre à cette question, à la fois les données de terrain (en Chine du Sud), les expériences de laboratoire (en France) et la formulation de concepts sont mobilisées. Les résultats sont organisés en deux chapitres. Le premier pose la question de l’efficacité de la présence de racines pour stabiliser les pentes, tous d’abord sous l’angle des processus mécaniques, puis sous l’angle des processus hydriques. Le deuxième chapitre permet d’identifier un panel de traits pertinents et non redondants évaluant l’efficacité d’une espèce pour la stabilisation des pentes puis s’appuie sur ce panel afin de sélectionner les espèces chinoises les plus efficaces. Enfin, la discussion aborde les limites de ce travail et propose de nouvelles pistes de recherche.Du point de vue mécanique comme du point de vue hydrique, c’est la conjonction des effets des racines de structure et des racines fines qui importe. Les racines de structure sanas racines fines ne sont pas optimales et peuvent même faire apparaître des lignes de fragilité. Plus précisément, les racines de structure sont particulièrement bienvenues vers l’aval de la pente pour des raisons à la fois mécaniques et hydriques. Les racines fines seules ne sont pas optimales non plus, elles peuvent faire apparaître localement des zones de faiblesse qui, si elles sont proches, participeront au déclenchement d’un glissement de terrain. Des ramifications racinaires denses améliorent la stabilité mécanique. Orientées vers l’aval de la pente, elles améliorent la stabilité hydrique. Les autres traits racinaires pertinents pour évaluer l’efficacité des racines à stabiliser le sol sont la contrainte et la déformation maximale en tension, la concentration en azote et la concentration en sucres solubles. / China is currently facing serious environmental issues and is listed among the countries that contribute most to pollution and destruction of the global environment. Particularly, Southern China is naturally prone to landslides because of unfavourable tectonic, climatic and anthropogenic conditions. Since the late 1990s, the Chinese government has implemented policies of large-scale reforestation, but the question of the most suitable species is still pending. The introduction of this thesis presents the different types of landslides, the context in Southern China and what eco-engineering means, in order to clarify the boundaries within which this work is situated. Thus, this study (i) limits itself to the study of superficial landslides, (ii) fits into the requirement scheme of low-cost solutions using local plant species, and (iii) focuses on the root, plant and hotspot degradation scales. Within those geographical, sociological, political and scientific frameworks, this thesis aims to answer the following scientific question: which species and root architectures are the most efficient to stabilize the steep slopes in Southern China? To answer this question, field data (in Southern China), laboratory experiments (in France) and the formulation of concepts are mobilized. The results are organized into two chapters. The first chapter identifies a panel of relevant and nonredundant traits assessing a given species effectiveness in slope stabilization, and then draws on that panel to select the most efficient Chinese species. The second chapter raises the question of the effectiveness of the presence of roots to stabilize slopes, first in terms of mechanical processes, then in terms of hydraulic processes. Finally, the discussion addresses the limitations of that work and suggests new avenues of research. Root traits relevant to assessing the root effectiveness to soil stabilization are maximum tensile stress and strain, nitrogen concentration as well as concentration in water-soluble sugars. The most efficient species among nine pioneer species measured on the Chinese slopes are Pueraria stricta, a legume native from Southeast Asia which plantation happened from reforestation programs, and Artemisia codonocephala, a spontaneous Asteraceae native from Southern China. Recommendations regarding the nine species are presented for the use of their characteristics in eco-engineering. From the mechanical as well as the hydraulic viewpoint, the conjunction of structural roots and fine roots is determinant. Structural roots alone are not optimal and may even bring up lines of weakness. Specifically, for both mechanical and hydric reasons, structural roots are particularly efficient when they grow downslope. Fine roots alone are not optimal either, as they can produce local areas of weakness which, if they are close, can participate in the triggering of a landslide. The branching organization is also particularly important: dense throughout the root profile, branches improve the mechanical stability. Oriented downslope, branching forks improve underground water flow and thus hydraulic stability. The limits of this thesis point out the difficulty to choose indicators and to follow their evolution over time. Another limitation lies in the difficulty to assess the relationship between roots and soil, as the only root resistance is not sufficient to prevent soil from sliding. Finally, the spatial integration of root properties remains challenging. In conclusion, this thesis contributes to improve the knowledge of the plant material available in the mountains of Southern China. Its results will optimize eco-engineering actions related to slope stability. It also upgrades the knowledge about processes at stake between roots and their environment during a landslide