Master of Science / Department of Plant Pathology / Karen A. Garrett / Ari Jumpponen / Traditional fallow periods in the Bolivian highlands are being shortened in an effort to increase short-term crop yields, with potential long-term impacts on soil communities. Using 454-pyrosequencing, we characterized fungal and bacterial community responses to (1) the length of fallow period and (2) the presence of the plants Parasthrephia sp. or Baccharis sp. (both locally known as ‘thola’). Thola is widely considered by farmers as beneficial to soil health, although it is also frequently harvested as a source of fuel by farmers. Soils in one study area, Ancoraimes, had higher levels of organic matter, nitrogen and other macronutrients compared to the other study area, Umala. In our analyses, Ancoraimes soils supported more diverse fungal communities, whereas Umala had more diverse bacterial communities. Unexpectedly, the longer fallow periods were associated with lower fungal diversity in Umala and lower bacterial diversity in Ancoraimes. Fungi assigned to genera Verticillium, Didymella, and Alternaria, and bacteria assigned to genera Paenibacillus, Segetibacter, and Bacillariophyta decreased in abundance with longer fallow period. The presence of thola did not significantly affect overall soil fungal or bacterial diversity, but did increase the frequency of some genera such as Fusarium and Bradyrhizobium. Our results suggest that fallow period has a range of effects on microbial communities, and that the removal of thola from the fields impacts the dynamics of the soil microbial communities.

Stress activates a number of endocrine pathways that alter an animal's physiology in a manner which can result in undesirable meat quality. Animals frequently exhibit meat quality defects, including ecchymosis, at slaughter due to the stress of slaughter. This thesis explores how stress related hormones interact with adrenergic receptors to alter muscle and vascular physiology. Fallow deer were exposed to either a transciptional regulator (hydrocortisone), a beta adrenergic recptor agonist (clenbuterol) or a beta adrenergic receptor antagonist (propranolol). The administration of hydrocortisone resulted in a negative feed-back type reduction in circulating cortisol. Animals treated with propranolol and clenbuterol displayed less severe eccymosis. These results indicated that the beta 2 adrenergic receptor (B2AR) is important in controlling ecchymosis severity. B2AR was also found to be important in mediating vascular dynamics, growth and energy pathways. To investigate how adrenergic receptors alter skeletal muscle gene expression and meat quality, an in vivo wistar rat model was developed in conjunction with in vitro muscle cell (L6) experiments. Gene expression of B2AR, its associated kinase (BARK) and collagen type III, prolyl- 4-hydroxylase (P4Hy) was measured in rat muscle and L6 cells. Following exposure to clenbuterol and hydrocortisone, growth and meat quality were determined. The L6 experiments revealed that gene expression following exposure to hydrocortisone and B2AR ligands paralleled the in vivo rat changes in B2AR, BARK, collagen type III, and P4Hy gene expression. In both L6 and wistar rat models the B2AR and BARK genes are similarly expressed following clenbuterol exposure. Both rats and deer exposed to clenbuterol had significant increases in growth rate and a reduction of intramuscular fat. The B2AR therefore appears to be a major mediator of many interrelated events including energy distribution, growth and vascular response to stress. Habituating animals to stress stimuli may increase their coping ability and improve welfare and meat quality. / Doctor of Philosophy (PhD)

ALMEIDA, Cícero Lima de. Impacto da recuperação de área degradada sobre as respostas hidrológicas e sedimentológicas em ambiente semiárido. 2011. 132 f. : Dissertação (mestrado) - Universidade Federal do Ceará, Departamento de Engenharia Agrícola, Programa de Pós-Graduação em Engenharia Agrícola, Fortaleza-CE, 2011. / Submitted by demia Maia (demiamlm@gmail.com) on 2016-06-17T13:36:15Z No. of bitstreams: 1 2011_dis_clalmeida.pdf: 3766101 bytes, checksum: 4476b1021ccb20f6b1f9c8caaabe3473 (MD5) / Approved for entry into archive by demia Maia (demiamlm@gmail.com) on 2016-06-17T13:39:51Z (GMT) No. of bitstreams: 1 2011_dis_clalmeida.pdf: 3766101 bytes, checksum: 4476b1021ccb20f6b1f9c8caaabe3473 (MD5) / Made available in DSpace on 2016-06-17T13:39:51Z (GMT). No. of bitstreams: 1 2011_dis_clalmeida.pdf: 3766101 bytes, checksum: 4476b1021ccb20f6b1f9c8caaabe3473 (MD5) Previous issue date: 2011 / As regiões semiáridas compreendem áreas muito sensíveis às alterações do seu ambiente natural. O semiárido brasileiro, por ser um dos mais populosos do mundo, está mais susceptível às atividades antrópicas, como o desmatamento para atividades agrosilvopastoris. Esta pesquisa foi desenvolvida no âmbito do projeto “Estudos dos processos de degradação/desertificação e suas relações com o uso da terra em sistemas de produção no semiárido cearense: o caso da microrregião de Sobral – Ceará”. A área experimental localiza-se no município de Irauçuba, inserida em um dos núcleos de desertificação do semiárido brasileiro. O clima da região é do tipo quente e semiárido com chuvas de verão (média anual de 530 mm) e índice de aridez 0,34. O solo é do tipo Planossolo Nátrico Órtico típico, A fraco; e a vegetação nativa é do tipo Caatinga arbustiva aberta. A principal atividade econômica da região é a pecuária extensiva (bovino e ovino) em sobrepastejo, sem uso de práticas conservacionistas. O presente trabalho tem como objetivo comparar os processos hidrossedimentológicos de duas encostas em ambiente semiárido: uma (370 m²) está submetida à prática de pousio desde 2000; enquanto que a outra (468 m²) se encontra degradada, sendo usada como área de pastagem há mais de vinte anos. As duas encostas possuem as mesmas condições de solo, clima e relevo, diferenciando-se somente quanto ao uso e à cobertura do solo. São comparadas analiticamente variáveis hidrológicas e sedimentológicas. Os experimentos foram realizados entre 01 de janeiro de 2010 e 15 de abril de 2011. Para promover essa comparação foram coletados dados de precipitação (lâmina e intensidade), escoamento superficial e perda de solo. A precipitação foi de 264 mm em 2010 e de 445 mm até 15 de abril de 2011, tendo sido registrados 55 eventos nos 16 meses. As chuvas de Irauçuba demonstraram alta variabilidade espacial: há diferença estatística (nível de significância de 5%) entre os dois pluviômetros usados na pesquisa, embora estejam a uma distância de apenas 200 m. O padrão hidrológico das chuvas na região é de intermediário a atrasado (70% dos eventos), o que causa maior potencial erosivo. Conclui-se, a partir da análise comparativa, que os dez anos de pousio reduziram em 60% o escoamento superficial em relação à encosta degradada. A menor precipitação capaz de gerar escoamento superficial foi 7,2 mm na encosta degradada, enquanto que esse valor foi de 8,6 mm para a encosta em pousio. Isso demonstra o incremento de abstração inicial da encosta preservada, ou seja, sua maior capacidade de retenção de umidade. O incremento da capacidade de retenção se dá através da interceptação vegetal, da serrapilheira e da camada superficial do solo. No entanto, observou-se que a maior precipitação incapaz de gerar escoamento superficial foi idêntica (17 mm) nas duas encostas. A explicação para tal resultado é que o parâmetro dominante nesse processo é a estrutura do solo: embora haja diferenças na superfície dos solos, os dez anos de pousio ainda não foram capazes de alterar sua estrutura, conforme avaliou Sousa em pesquisa independente. Observou-se que a taxa de decaimento da vazão foi sensivelmente afetada pela prática de pousio: a taxa, de 0,107 min-1 na encosta degrada, decresceu para 0,045 min-1 na encosta preservada. A menor taxa de decaimento de vazão na encosta em pousio indica o início da recuperação de seu escoamento de base, o que favorece maior permanência da água no corpo hídrico. Os dez anos de pousio também foram capazes de reduzir a perda de solo. Essa redução, de 83% em relação à encosta degradada, induz à melhoria das condições físicas, químicas e biológicas do solo, responsáveis pelo incremento da produção vegetal. Conclui-se, com base nos experimentos aqui realizados, que os dez anos de pousio melhoraram, de modo mensurável, as condições hidrológicas e sedimentológicas na encosta semiárida. A prática de pousio, portanto, pode ser adotada para fins de recuperação de áreas de Caatinga degradada. Sugere-se que sejam realizadas novas investigações, que avaliem a associação dessa prática a outras, a fim de intensificar o processo de recuperação de áreas degradadas no semiárido

Aktuell gibt es für Selen (Se) keine Bedarfsempfehlungen für das Damwild (Dama dama) in Gehegehaltung. Diese Studie soll die typische Se-Aufnahme bei Gehegehaltung von Damwild ermitteln und klären, welche Parameter sich eignen, um die Se-Versorgung des Damwildes zu reflektieren. Dazu wurden 19 Damhirsche in zwei Gruppen unter identischen Bedingungen gehalten. Die Tiere ernährten sich von dem natürlichen Grasaufwuchs und Mischfutter (0,15 mg/kg TS bzw. 1,07 - 1,91 mg/kg TS). In Blut, Plasma und die Organen wurden der Se-Gehalt, die Aktivität der Se-abhängigen Glutathionperoxidase (GPx) sowie teilweise die Gesamt-GPx-Aktivität (gesGPx), die Aktivität der Glutathion-S-Transferase (GST) und die Expression verschiedener GPx analysiert. Durch die Se-Supplementierung wurden ein signifikanter Anstieg des Plasma-Se in der Versuchsgruppe und ein moderater Unterschied der Vollblut-Se-Konzentration sowie der Vollblut-GPx-Aktivität zwischen der Kontroll- und der Versuchsgruppe beobachtet (p = 0,08). Außerdem wurde in allen Organen der Versuchsgruppe ein höherer Se-Gehalt als in der Kontrollgruppe festgestellt. In der Hierarchie der untersuchten Organe ist die Niere am höchsten angeordnet, absteigend folgen der Herz- und Skelettmuskel, die Milz und die Leber. Eine Se-Aufnahme von 0,05 - 0,08 mg/kg TS führt beim Damwild nicht zur Ausprägung von Se-Mangelsymptomen und stellt daher eine ausreichende Se-Versorgung dar. Die Empfehlungen zur Se-Versorgung für Damwild sind somit nicht von Hauswiederkäuern zu übernehmen. Im Plasma und im Vollblut scheinen Se-Konzentrationen von 28 - 64 µg/l und 81 - 200 µg/l für eine ausreichende Se-Versorgung zu sprechen, in der Leber Se-Konzentrationen von 270 - 663 µg/kg TS.:Inhaltsverzeichnis Inhaltsverzeichnis I Abbildungsverzeichnis V Tabellenverzeichnis VI Verzeichnis der Anhangstabellen VIII Abkürzungsverzeichnis IX 1. Einleitung 1 2. Literaturübersicht 2 2.1 Se als chemisches Element 2 2.2 Geschichte des Se und seiner Proteine 3 2.3 Se-Gehalte in Boden, Pflanzen, Nahrungs- und Futtermitteln 4 2.3.1 Se-Gehalte im Boden 4 2.3.2 Se-Gehalte in Pflanzen 5 2.3.3 Se-Gehalte in Nahrungsmitteln 7 2.3.4 Se-Gehalte in Futtermitteln 8 2.4 Se im Stoffwechsel 9 2.4.1 Resorption 9 2.4.2 Transport, Metabolismus und Speicherung 10 2.4.2.1 Transport 10 2.4.2.3 Speicherung 11 2.4.3 Versorgung über Plazenta und Milch 12 2.4.4 Exkretion 14 2.5 Biologische Funktionen des Se 16 2.5.1 SeP 16 2.5.2 Funktionen 18 2.5.2.1 Spezielle Funktionen der GPx 18 2.5.2.2 Weitere Funktionen der Selenoenzyme 20 2.6 Damwild (Dama dama) 21 2.6.1 Systematische und historische Einordnung des Damwildes 21 2.6.2 Physiologie und Ernährung des Damwildes 22 2.6.3 Se-Status bei Cerviden 23 2.7 Se-Bedarf 24 2.8 Se- und Enzymwerte im Organismus 25 2.8.1 Se-Gehalte im Blut 25 2.8.2 Se-Gehalte in verschiedenen Organen 28 2.9 Se und Erkrankungen 30 2.9.1 Se-Mangel assoziierte Erkrankungen 30 2.9.2 Se-Toxizität 31 2.9.2.1 Die akute Se-Intoxikation 32 2.9.2.2 Die subakute Se-Intoxikation 33 2.9.2.3 Die chronische Se-Intoxikation 33 3 Tiere, Material und Methoden 35 3.1 Versuchsziel 35 3.2 Tiere 35 3.3 Haltung 35 3.4 Fütterung und Supplementierung 35 3.5 Versuchsablauf 37 3.6 Probenentnahmen 38 3.6.1 Blutproben 38 3.6.2 Organ- und Gewebeproben 38 3.6.3 Wiegen 40 3.6.4 Futterproben 41 3.7 Versuchsparameter 43 3.8 Analytische Methoden 43 3.8.1 Futteranalyse 43 3.8.1.1 TS 43 3.8.1.2 Rohasche (Ra) 44 3.8.1.3 Organische Substanz (oS) 44 3.8.1.4 Rohprotein (Rp) 44 3.8.1.5 Rohfett (Rfe) 44 3.8.1.6 Rohfaser (Rfa) 44 3.8.1.7 N-freie Extraktstoffe (NfE) 45 3.8.1.8 Spurenelemente: Se, Cu, Zn 45 3.8.2 Vollblut-, Plasma-, Organ- und Gewebeanalyse 45 3.8.2.1 Histologie der Skelettmuskulatur 45 3.8.2.2 Se-Gehalt 46 3.8.2.3 TS-Gehalt 47 3.8.2.4 GPx-Aktivität 47 3.8.2.5 Proteingehalt 48 3.8.2.6 Hämoglobingehalt 49 3.8.2.7 GPx-mRNA-Expression 49 3.8.2.8 α -Glutathion-S-Transferase-Aktivität (GST) 53 3.9 Statistische Auswertung 54 4. Ergebnisse 55 4.1 KM der Tiere und Gewichte der Schlachtkörperhälften 55 4.1.1 KM der Tiere zu Versuchsbeginn 55 4.1.2 Gewichte der Schlachtkörperhälften zu Versuchende 55 4.2 Histologie der Skelettmuskulatur 56 4.3 Se-Gehalte in Plasma, Vollblut und Organen 58 4.3.1 Se-Gehalte in Plasma und Vollblut 58 4.3.2 Se-Gehalte in verschiedenen Organen 59 4.4 Se-abhängige und -unabhängige Enzyme 60 4.4.1 GPx-Aktivitäten in Plasma und Vollblut 60 4.4.2 GPx-Aktivität in verschiedenen Organen 62 4.4.3 GPx-mRNA-Expression 63 4.4.4 α-GST-Aktivität 64 5. Diskussion 67 5.1 Kritik der Methoden 67 5.1.1 Se-Supplementierung der Tiere 67 5.1.1.1 Futteraufnahme 67 5.1.1.2 Höhe der Se-Supplementierung 67 5.1.1.3 Dauer der Se-Supplementierung 68 5.1.1.4 Art der Se-Supplementierung 68 5.1.2 Probengewinnung 69 5.1.3 Untersuchungsparameter 69 5.1.4 Vitamin E 69 5.2 Diskussion der Versuchsergebnisse 70 5.2.1 Einschätzung der Se-Versorgung vor Se-Supplementierung 70 5.2.2 Einschätzung der Se-Versorgung nach unterschiedlicher Se-Supplementierung 72 6. Zusammenfassung 81 7. Summary 83 8. Literaturverzeichnis 85 9. Anhang……………………………………………………………………..110 Danksagung 117

No description available.

Organic matter (OM) is a multi-purpose tool in West African smallholder mixed-farming systems, but its supply has been decreasing for several decades. To assess the viability of a mixed-farming system of south Senegal, carbon (C), nitrogen (N) and phosphorus (P; available in soil and noted POD) budgets (stocks and flows) were thus quantified.The village territory of the study showed a ring-like organisation with growing intensification of fertilization and cropping practices from the periphery (bush ring) to the compounds (compound fields).Stocks in plant and soil averaged 54.7 tC, 2.63 tN and 43.5 kgP ha 1 in old fallows. They were 97, 29 and 251 % higher than in the bush cropped fields, plant biomass accounting for nearly all of the rise. C, N and P amounts recorded in the soil of compound fields were higher than those of the bush field, but the increase was restricted mainly to the 0 10 cm layer. However, the rather weak response of local sandy soils to management can be interpreted only by reassessing the bio-thermodynamical signification of soil organic carbon cycling in the maintenance of the integrity of local agroecosystems.Manageable stocks of the whole village territory were estimated to 29.7 tC, 1.52 tN and 28.6 kgP ha 1 in 1997. Carbon was stored mainly in soil. Livestock, crop harvest and wood collecting were responsible for respectively 59, 27 and 14 % of the C uptake on the village territory. As a result, large C flows were set towards the compound ring (3.8 tC ha 1 y 1). N and P depletion of the system amounted to 4 kgN and 1 kgP ha 1 y 1, suggesting that the system was close to nutrient balance.Under current demographic growth rate, C depletion may reach 0.38 tC ha 1 y 1 and C demand may double during the next three decades. Without any intensification of farming practices, the viability of the system might soon be called into question.

In der vorliegenden Dissertation wird die Bedeutung von Brachen für Artenvielfalt und Stabilität von Blüte-Bestäuber-Nahrungsnetzen in agrarisch genutzten Landschaften anhand ausgewählter blütenbesuchender Insektengruppen (Syrphidae, Lepidoptera) untersucht. Die Freilandarbeiten fanden von 1998-2000 im Raum der Feldberger Seenlandschaft, Mecklenburg-Vorpommern, statt. Es werden die beiden Hauptnahrungsquellen Nektar und Pollen betrachtet, dabei fanden Untersuchungen zur Intensität der Blüte-Bestäuber-Interaktion auf Stilllegungsflächen, zum flächenbezogenen quantitativen Nektarangebot im Jahresverlauf, zur individuellen Pollennutzung bei Syrphiden und zur Breite und Überlappung der Nahrungsnischen bei den dominanten Arten Episyrphus balteatus, Metasyrphus corollae, Syritta pipiens und Sphaerophoria scripta statt.<br /> <br /> Im Ergebnis zeigt sich eine hohe Bedeutung der Brachflächen für die Stabilität des Blüte-Bestäuber-Netzes, während die Diversität von anderen, eher landschaftsbezogenen Faktoren abhängig ist. / This dissertation examines the importance of fallow land for the diversity and stability of pollination webs in agricultural landscapes as exemplified by selected groups of anthophilous insects (syrphidae and lepidoptera). The field studies were carried out between 1998 and 2000 in the Feldberg lakeland area in the north-east German State of Mecklenburg-Western Pomerania. Observations were made of nectar and pollen as the two main sources of food. Studies were conducted into the intensity of plant-pollinator interaction in set-aside areas, the site-specific quantity of nectar available during the vegetation period and the individual pollen intake of syrphid flies. Different methods were employed to establish the breadth of the trophic niches among the predominant species (Episyrphus balteatus, Metasyrphus corollae, Syritta pipiens and Sphaerophoria scripta) and the extent to which they overlapped. <br /> <br /> The studies showed that, while fallow land is very important for the stability of plant-pollinator food webs, their diversity depends on other factors that are more closely related to the landscape.

As planted forests mature and are clearfelled in patches, second rotation tree crops (restocks) become available to black grouse, a species of conservation concern in the UK. Currently, only a limited amount is known about the resources provided by this habitat to black grouse and their broods. The aims of this study therefore, were to investigate the recovery of field-layer vegetation and the invertebrate population from restock through to canopy closure of planted trees, assess the duration of habitat availability and food resources to black grouse, and understand how forest management could improve provision. Changes to the abundance of predators resulting from habitat management were also considered. The comparative habitat quality of restocks was assessed in a wider landscape context. Field-layer vegetation in 72 restocks in two afforested areas in the north-east and the south-west of the Scottish Highlands was surveyed. On average, only 60% of ground in restocks was re-planted with second rotation trees, with the remainder left unplanted. Initial vegetation recovery was generally impeded by timber harvest residues (mainly brash), which comprised up to 50% of total ground cover two years after restock. Increased cover of heather Calluna vulgaris, often an important component of black grouse habitat, and decreased brash cover were recorded in areas of restocks where first-rotation timber was removed by cable-winch (compared with harvester and forwarder removal) and in planted areas (compared with areas left unplanted). Bilberry Vaccinium myrtillus and cotton grass Eriophorum spp. occurrence was recorded infrequently irrespective of restock age or management. Heather generally dominated the field-layer six years after restock, reaching a height and density reported to be suitable for black grouse nesting and brood cover in other studies. The onset of tree canopy closure as early as eight years suggests that suitable black grouse habitat availability in restocks is likely to be severely limited in duration. Brash removal, or break-up and re-distribution of the brash layer, positively affected the recovery of field-layer vegetation species potentially of use to black grouse. Extending the fallow period prior to restock resulted in an extended period of suitable habitat available to black grouse prior to canopy closure. However, habitat created by extending the fallow period also attracted a higher number of mammalian predators of black grouse. In the longer term, areas of restocks left unplanted should provide a valuable open-ground resource after canopy closure of the planted crop, although results suggest that management to prevent encroachment of naturally regenerating non-native trees is likely to be necessary. Invertebrate taxa selected by chicks in previous black grouse studies were available in all ages of restock studied. Taxa abundance differed as restocks aged and field-layer vegetation developed, although contrasting habitat preferences of taxa meant that each was affected differently by restock management. No single forest management method positively increased abundance of all taxa. Abundance of Lepidoptera larvae, a key food item for black grouse chicks, was positively related to dwarf shrub cover. An extended fallow period prior to restock should prolong increased larvae availability to chicks. Provision of preferred field-layer vegetation habitat and invertebrate abundance in restocks was comparable to habitat surrounding leks - areas likely to be occupied and utilised by black grouse. Restocks had a comparatively low occurrence of key plant species, including bilberry Vaccinium myrtillus and cotton grass Eriophorum spp. Cover of the dwarf shrub bog myrtle Myrica gale, positively associated with Lepidoptera larvae abundance in habitat surrounding leks, was absent from restocks. The abundance of other invertebrate taxa considered was similar between leks and restocks. Study findings are discussed with reference to black grouse conservation and commercial forestry systems in Europe. Management recommendations to improve habitat for black grouse in second rotation planted forests in Britain are provided.

Research object. Populations of cervine animals (moose, red deer, roes) and their living environment in Mikieriai Forestry of the Public Institution Anykščiai Forest Enterprise. Research aim. To study the populations of cervine animals, their living environment and effect of these animals on forest in Mikieriai Forestry of the Public Institution Anykščiai Forest Enterprise. Research methods. Logic analysis of literature and systemic selective accounting. Research results. Cervine animals living in the forests of the Forestry are moose (density 7 pcs./1000 ha), red deer (12 pcs./1000 ha), roes (31 pcs./1000 ha). Because of their effect on forest planting and sprouts the number of cervine animals should be reduced as they browse, break stems and peel bark. The use of cervine animals is low. Before breeding fallow-deer in the forests of the Forest the basic breed should be moose, secondary – roe, minor secondary – red deer. When the fallow-deer are bred, to which the forests of the Forestry are good to live in and belong to the category of middle areas, the basic breed in the forests of the Forestry should be moose, secondary – roe and fallow-deer, minor secondary (undesirable) – red deer. From possible effect of cervine animals the forest planting and sprouts are protected by fences and repellents and protected area makes up 4,8 – 6,2% of the total area of the forests. Many recommended stimulants in biosphere range are also favourable for the increase of hunting fauna. The... [to full text]

Le Sahel est particulièrement exposé à la variabilité de la mousson Ouest-Africaine dont les répercussions socio-économiques peuvent prendre un caractère dramatique. Cette région est en outre confrontée à l'une des plus fortes croissances démographiques jamais observées, se traduisant par une pression toujours plus forte sur de faibles ressources naturelles et un environnement fragile. Dans ce contexte, un enjeu important se situe dans notre capacité à proposer des outils aidant au suivi des ressources hydriques et végétales, et permettant d'anticiper les impacts climatiques et anthropiques à moyen terme sur ces ressources. Pour cela, il est indispensable d'étudier et mieux comprendre les processus d'échanges d'énergie et de matière à l'interface terre-atmosphère, qui contribuent à la régulation de la mousson d'une part et gouvernent le cycle hydrologique local et le développement végétal d'autre part. Les travaux réalisés s'inscrivent dans cette problématique, portant précisément sur l'analyse des cycles de l'eau et de l'énergie en région sahélienne sous les effets combinés du climat et de l'activité humaine. La démarche s'appuie sur une méthodologie alliant observations in situ et modélisation à base physique. L'étude a été réalisée dans la région centrale du Sahel, dont le système agricole traditionnel associe pastoralisme et cultures pluviales en alternance avec la jachère. Elle s'est appuyée sur le réseau d'observations éco-hydrologiques et énergétiques acquises en continu durant 7 années (2005-2012) par l'Observatoire AMMA CATCH au Sud-Ouest Niger. La qualité et la cohérence de ces observations ont permis de dresser des grands traits du fonctionnement éco-hydrologique des deux couverts végétaux les plus répandus dans la région : cultures de mil et jachères arbustives. Les observations ne permettent cependant pas à elles seules d'établir des bilans complets aux différentes échelles temporelles d'intérêt (infra-journalière à interannuelle). Une modélisation couplée détaillée des cycles de l'énergie et de l'eau a par conséquent été élaborée pour ces deux couverts, à l'aide du modèle de transferts sol-plante-atmosphère SiSPAT. Etalonné sur une période de 2 ans, le modèle a ensuite été validé sur les 5 autres années d'observation, en contraignant les paramètres du modèle à des valeurs physiquement réalistes. En bon accord avec les observations, cette modélisation pluriannuelle s'est révélée être un outil d'analyse précieux, intégrant toute la pertinence, la richesse et la cohérence du jeu de données. La représentativité de la période étudiée a permis d'en exploiter les résultats pour (1) analyser l'impact de la variabilité climatique sur les bilans d'eau et d'énergie aux différentes échelles temporelles et (2) fournir une première climatologie des flux et stocks d'eau et d'énergie à l'interface sol-végétation-atmosphère, à ces mêmes échelles. Les similitudes et différences de fonctionnement éco-hydrologique et énergétique entre écosystèmes ont été mises en évidence. Par exemple, l'évapotranspiration représente plus de 80% des précipitations annuelles et près de la moitié du rayonnement global au cœur de la mousson pour les deux sites. Sa distribution saisonnière et son partitionnement en évaporation du sol et transpiration des plantes diffèrent néanmoins entre les deux écosystèmes, tout comme le ruissellement, et le drainage sous la zone racinaire. Ce dernier apparaît significatif pour le champ de mil mais pas pour la jachère. Une analyse de sensibilité des processus aux caractéristiques du sol et du couvert a été réalisée. La robustesse des résultats produits devrait leur permettre de servir de référence pour les études des processus hydrologiques et énergétiques dans cette région. La modélisation ainsi construite présente un potentiel évident pour des études prospectives, relatives notamment au changement climatique ou à une évolution des pratiques agricoles. / The Sahel region is particularly exposed to the variability of the West African Monsoon, which may lead to dramatic socio-economical consequences. This region also has one of the highest demographic growth rates, resulting in an ever-increasing pressure on the scarce natural resources and fragile environment. In this context, a major challenge lies in our ability to provide appropriate tools for the monitoring of hydrological and vegetation resources. These tools should also be suitable for the prediction of climatic and anthropogenic impacts in the medium term. This requires a better understanding of energy and matter transfer processes at the earth-atmosphere interface. Indeed, the latter both play a role in the regulation of the monsoon and also drive the local hydrological cycle and vegetation development. The present research follows such a framework and consists specifically in analyzing the water and energy cycles in the Sahel region under the combined effects of climate and human activity. This is undertaken by developing a methodology combining the use of in situ observations and physically-based modelling. The study was conducted in the central Sahel, where traditional agricultural systems are formed by the association of pastoralism and rain-fed crops in rotation with fallow cycles. This study was based on the network of eco-hydrological and energy data acquired continuously during 7 years (2005-2012) by the South-West Niger AMMA-CATCH Observatory. Quality and consistency of these observations allowed analyzing the main features of the eco-hydrological functioning of the two main land-covers in the region: millet and fallow savannah. However, observations alone were not sufficient to compute comprehensive water and energy budgets at all the different time scales of interest (sub-daily to inter-annual). A detailed modelling of coupled water and energy cycles was therefore undertaken for these two land-covers, using the soil-vegetation-atmosphere transfer model SiSPAT. The model was first calibrated on a 2-year period, and further validated on the remaining 5-year observations, by constraining model parameters to physically realistic values. This multi-year modelling was in good agreement with the observations, and provided a precious analysis tool that integrated the relevance, richness and consistency of the dataset. Thanks to the representativeness of the studied period, results served at the different temporal scales to (1) analyze the impact of climatic variability on water and energy budgets and (2) produce a preliminary climatology for the water and energy fluxes and storages at the soil-vegetation-atmosphere interface. Similarities and differences in eco-hydrological and energy functioning between ecosystems were evidenced. For instance, evapotranspiration represented more than 80% of annual precipitations and close to half of the global radiation at the heart of the monsoon for both sites. Seasonal distribution and partitioning of evapotranspiration between soil evaporation and plants transpiration differed between the two ecosystems, as well as the runoff, and the drainage below the root zone which appeared significant for the millet field but not for the fallow site. A sensitivity analysis of the energy and water budgets to soil and vegetation characteristics was conducted. Robustness of the produced results should enable them to serve as reference for studies of water and energy processes in this region. The resulting calibrated model showed an obvious potential for prospective studies, such as those on climate change or on the evolution of agricultural practices.