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Microorganisms and their interactions in soil play a critical role in nutrient transformations and cycling, and in sustaining soil productivity. Arbuscular mycorrhizal fungi (AMF) are a keystone group of fungi influencing nutrient cycling. In turn, the activity and composition of microorganisms in soil are influenced by management practices such as the choice of crop species and fertilization. Long-term effects of cropping, manuring and mineral fertilization on the soil-plant system were defined in three selected agro-ecosystems of Canada. A greenhouse experiment was also conducted to define the involvement of AMF in organic residue decomposition and nitrogen (N) mineralization.<p> In the greenhouse experiment, pasteurized soil was inoculated or not with a strain of <i>Glomus claroideum, G. clarum</i> or <i>G. intraradices</i>. 15N-labelled organic residue in a nylon mesh was buried in the soil. The fate of residue-N was determined after 24 weeks. Arbuscular mycorrhizal fungal species enhanced mineralization of organic residue to different degrees. The highest recovery of mineralized N by plants (25%) occurred when inoculated with <i>G. clarum</i>. The AMF enhanced N-mineralization differentially leading to differential plant growth stimulation, differences in the C-to-N ratio of the decomposing organic residue, and in soil microbial community structure.<p> In a field trial conducted on a Brown Chernozemic soil at the Semiarid Prairies Agricultural Research Centre in Swift Current, SK, eight years of phosphorus (P) (0, 20 and 40 kg P2O5 ha-1) application to alfalfa monoculture and alfalfa-Russian wildrye (RWR) dual culture modified the soil microbial community structure. Low levels of phosphorus (0 and 20 kg P2O5 ha-1) fertilization in alfalfa-RWR dual culture increased the abundance of fungivorous nematodes and grazing of AMF hyphae thus increasing the carbon drain from plants and ultimately reducing plant biomass.<p> In a sub-humid region of Saskatchewan on a a Black Chernozem soil, mineral N (0, 20 or 40 kg N ha-1) was applied for 10 years to pea grown continuously or in rotation with wheat. Lower yields in continuous-pea were associated with reduced abundance of beneficial Gram positive bacteria and AMF, and an increase in uptake of plant available Fe to toxic levels. These differences in soil properties were related to root rot which increased with years in continuous-pea. The soil environment in the continuous-pea rotation further led to lower organic carbon inputs, and to reduced soil microbial biomass and soil enzyme activity indicating a negative impact on nutrient cycling.<p> In the south coastal region of Agassiz, British Columbia, dairy manure slurry (DMS) and ammonium nitrate (AN) had been applied on a Regosol at the same annual rate of mineral N (50 or 100 kg mineral N ha-1) for nine years to perennial tall fescue, followed by one year of stand renovation through reseeding without fertilization. The multi-year application of DMS improved soil organic C, soil organic N, light fraction of organic matter, microbial biomass and enzyme activity as compared to mineral fertilization but the DMS-related increase in soil yield potential was lost in the process of stand rejuvenation. Dairy manure slurry application based on the crop N requirement also increased soil phosphate indicating increased environmental hazard. In conclusion, long-term use of DMS in multi-cut tall fescue can increase soil quality parameters but can also increase the risk of eutrophication of water bodies.<p> Overall, data showed that higher levels of soil nutrients can select for certain bacteria while AMF and other bacteria are more abundant under low soil fertility. On the other hand, different soil microbial groups were associated with different soil enzyme activities. From this study, I succeded in proving my hypothesis that practice of fertilization and choice of crop influence soil microbial community structure which further affect soil functioning.

Microorganisms and their interactions in soil play a critical role in nutrient transformations and cycling, and in sustaining soil productivity. Arbuscular mycorrhizal fungi (AMF) are a keystone group of fungi influencing nutrient cycling. In turn, the activity and composition of microorganisms in soil are influenced by management practices such as the choice of crop species and fertilization. Long-term effects of cropping, manuring and mineral fertilization on the soil-plant system were defined in three selected agro-ecosystems of Canada. A greenhouse experiment was also conducted to define the involvement of AMF in organic residue decomposition and nitrogen (N) mineralization.<p> In the greenhouse experiment, pasteurized soil was inoculated or not with a strain of <i>Glomus claroideum, G. clarum</i> or <i>G. intraradices</i>. 15N-labelled organic residue in a nylon mesh was buried in the soil. The fate of residue-N was determined after 24 weeks. Arbuscular mycorrhizal fungal species enhanced mineralization of organic residue to different degrees. The highest recovery of mineralized N by plants (25%) occurred when inoculated with <i>G. clarum</i>. The AMF enhanced N-mineralization differentially leading to differential plant growth stimulation, differences in the C-to-N ratio of the decomposing organic residue, and in soil microbial community structure.<p> In a field trial conducted on a Brown Chernozemic soil at the Semiarid Prairies Agricultural Research Centre in Swift Current, SK, eight years of phosphorus (P) (0, 20 and 40 kg P2O5 ha-1) application to alfalfa monoculture and alfalfa-Russian wildrye (RWR) dual culture modified the soil microbial community structure. Low levels of phosphorus (0 and 20 kg P2O5 ha-1) fertilization in alfalfa-RWR dual culture increased the abundance of fungivorous nematodes and grazing of AMF hyphae thus increasing the carbon drain from plants and ultimately reducing plant biomass.<p> In a sub-humid region of Saskatchewan on a a Black Chernozem soil, mineral N (0, 20 or 40 kg N ha-1) was applied for 10 years to pea grown continuously or in rotation with wheat. Lower yields in continuous-pea were associated with reduced abundance of beneficial Gram positive bacteria and AMF, and an increase in uptake of plant available Fe to toxic levels. These differences in soil properties were related to root rot which increased with years in continuous-pea. The soil environment in the continuous-pea rotation further led to lower organic carbon inputs, and to reduced soil microbial biomass and soil enzyme activity indicating a negative impact on nutrient cycling.<p> In the south coastal region of Agassiz, British Columbia, dairy manure slurry (DMS) and ammonium nitrate (AN) had been applied on a Regosol at the same annual rate of mineral N (50 or 100 kg mineral N ha-1) for nine years to perennial tall fescue, followed by one year of stand renovation through reseeding without fertilization. The multi-year application of DMS improved soil organic C, soil organic N, light fraction of organic matter, microbial biomass and enzyme activity as compared to mineral fertilization but the DMS-related increase in soil yield potential was lost in the process of stand rejuvenation. Dairy manure slurry application based on the crop N requirement also increased soil phosphate indicating increased environmental hazard. In conclusion, long-term use of DMS in multi-cut tall fescue can increase soil quality parameters but can also increase the risk of eutrophication of water bodies.<p> Overall, data showed that higher levels of soil nutrients can select for certain bacteria while AMF and other bacteria are more abundant under low soil fertility. On the other hand, different soil microbial groups were associated with different soil enzyme activities. From this study, I succeded in proving my hypothesis that practice of fertilization and choice of crop influence soil microbial community structure which further affect soil functioning.

Diss. (sammanfattning). Uppsala : Sveriges lantbruksuniv. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Univ., 2004. / Härtill 5 uppsatser.

Generalist predators can contribute to vital ecosystem services by potentially inducing trophic cascades as natural enemies of pests in agroecosystems. As the human population of the world gets larger, we need to produce more food on ever-smaller swaths of available land relying on ecosystem services, in the form of pest control, that may contribute to agricultural sustainability. Teasing apart the exact trophic linkages between predators and prey is a vital first step and essential to uncovering which predators are inducing trophic cascades and should be enhanced through conservation biological control. Combined with ecological experimentation, the main tool used throughout my research to identify trophic linkages is molecular gut-content analysis. I began by investigating mass sampling techniques and found they do not cause contamination in gut-content analysis and may be a simple method for collecting large numbers of cryptic predators for use in determining trophic linkages. Additionally, my research uncovered trophic interactions between stink bugs and generalist predators at multiple scales. Overall, I successfully designed molecular methods to investigate relationships between agricultural pests and generalist predators. A multi-year field study uncovered low predation on stink bug pests in contrast to previous research suggesting that generalist predators were contributing highly to biological control. This research highlights the need for replicated studies before making broad conservation biological control decisions. Although generalist predators were not consuming stink bugs in large numbers, my field cage study showed evidence of superfluous killing by spiders on adult stink bugs, highlighting the need to combine ecological studies with molecular methods to understand consumptive and non-consumptive effects on prey items. Gut-content analysis showed no evidence of consumption, but the field cage study allowed me to uncover the complicated relationships between spiders and stink bugs. In addition, I showed an invasive species can be detected in new areas through molecular gut-content analysis of predators before other sampling methods.

The purpose of this study was to evaluate the sustainability of agroecosystems. The framework developed within this study is systems-based with the dynamic linkages between the system components explicit. The primary objective of the study was to develop a computer model, the Sustainable Agroecosystem Model (SAM), that dynamically integrates the economic and ecological components of an agroecosystem. The model was used to assess the sustainability of agroecosystems, defined by ecodistrict boundaries, in the Brown soil zone of southwestern Saskatchewan. The SAM was comprised of three components: (1) a soils model that simulated soil and crop growth parameters; (2) an economic model that simulated land use and cropping decisions; and (3) a habitat model that calculated habitat and biodiversity parameters. These components were largely self-standing models comprised of important processes of the soil, economic and ecological sectors of the agroecosystem respectively. To simulate the co-evolutionary changes of the agroecosystem the component models were dynamically linked, based on a one year time step, through selected input and output parameters. The output of the component models reflect elements of the natural and man-made capital stock of the target agroecosystems and were used as sustainability indicators. The concept of strong sustainability was adopted in the analysis such that changes in these indicators signal changes in the relative sustainability of the system. The study focused on two types of simulations: (1) the relative sustainability of four ecodistricts was assessed using baseline simulations. This analysis highlighted the importance of biophysical constraints to the sustainability of an agroecosystem. These simulations indicated that the development of production technologies and policy initiatives, targeting agroecosystem sustainability, should explicitly consider the regional biophysical constraints faced by farms; and (2) the relative sustainability of a single ecodistrict subjected to economic (carbon credit and carbon tax policies) and environmental (climate change) perturbations was evaluated. These simulations highlighted the difficulty in identifying a single policy that leads to a sustainable agroecosystem. In general, policies that resulted in improvement in some components of the capital stock caused degradation of other components. The Identification of preferred policy, in terms of agroecosystem sustainability, requires a weighting of system effects based on societal preferences, ethical responsibilities, degradation thresholds and system co-evolution.

La connexion entre milieux aquatiques et terrestres a suscité l’intérêt de la communauté scientifique, notamment l’effet du transfert d’énergie et de matière sur le fonctionnement des écosystèmes adjacents. Beaucoup d’études se sont intéressées aux apports d’insectes aquatiques ailés dans les écosystèmes naturels, mais peu à leur impact en milieu agricole. En modifiant la production secondaire d’invertébrés aquatiques, les pratiques agricoles sont à même d’intensifier ou diminuer l’effet de ces apports aquatiques dans les terres agricoles et par conséquent la fourniture de services écosystémiques utiles à l’agriculture. Nous avons collecté des données d’émergences et de dispersion d’insectes aquatiques depuis plusieurs rivières dans des paysages agricoles. Les principaux groupes d’insectes émergents sont les trichoptères (56%), chironomidés (25%) et éphéméroptères (19%). Nous estimons la biomasse sèche émergente entre 1445 et 7374 mg m-2 an-1 selon les sites. Une majorité de ces insectes aquatiques se déposent sur une bande entre 0 et 10 mètres du bord de la rivière mais une proportion importante (45%) se dépose dans les cultures après 20 mètres. Nous apportons de nouvelles et prometteuses connaissances suggérant que les insectes aquatiques participent à la fourniture de plusieurs services écosystémiques (fertilisation, contrôle biologie, épuration de l’eau et pollinisation). En paysage agricole, une communauté d’insectes riche et abondant est nécessaire à la mise en place d’un système agricole durable. Nous pensons que le rôle des insectes aquatiques est à ce titre important et suggérons de nouvelles pistes de recherches pour l’agroécologie. / The connection between aquatic and terrestrial habitats has increased scientific interest in ecological subsidies, focusing on how the transfer of matter and energy between adjacent ecosystems can modify the ecosystems functioning. Much attention has focused on aquatic subsidies associated with winged aquatic insects in pristine areas, but their implication in agricultural landscapes is rarely considered. By altering the production of benthic macroinvertebrates, agricultural practices can increase or decrease the strength of aquatic subsidies and subsequently the provision of several ecosystem services to agriculture. We have monitored the emergence and inland dispersal of adult aquatic insects from several agricultural streams. Most emerging dry mass (DM) belong to Trichoptera (56%), Chironomidae (25%) and Ephemeroptera (19%). We estimate that annual emerging dry mass of aquatic insects ranged between 1445 and 7374 mg m-2 y-1 depending on stream. The majority of aquatic insects emerging falls between 0 and 10 meters from stream hedges. However, a great proportion (45%) though disperses and eventually falls after 20 meters from the stream. We provide new and promising evidence suggesting that winged stream insects can support several ecosystem services (soil fertilization, crop pest control, water purification and pollination). In agricultural landscapes, a rich and abundant insect community is necessary to promote sustainable practices, and we believe the role of aquatic subsidies in providing ecosystem services to agriculture is a new and promising field of research in agroecology.

Orientador: Elias José Simon / Resumo: O objetivo da agricultura é produzir alimentos e matérias-primas na qual a energia utilizada é fundamental. Análises energéticas de culturas revestem-se de igual importância às demais, sendo talvez aquela que traduz de forma privilegiada situações de maneira mais estrutural. Os agroecossistemas podem ser analisados e expressos sob a ótica energética e a determinação de índices que os avaliem devem merecer tratamento especial, visto que o itinerário técnico da cultura em termos de utilização de energia define graus de dependência com determinados sistemas produtivos. Do ponto de vista energético, gargalos de difícil superação não são recomendados e a análise energética, ao determinar índices que relacionam "entradas" e "saídas" de energia, é justificada enquanto instrumento complementar de avaliação. Observou-se a destacada importância da cultura do milho na agricultura brasileira, especialmente nos assentamentos rurais, e sua participação em diferentes formas de organização social da produção, inclusive na exploração agrícola familiar; a significativa demanda por terra no Brasil, expressando situação de relativa abundância de mão-de-obra; e os diversos itinerários técnicos percorridos até a produção final do grão. Assim, o presente trabalho objetivou determinar, a partir de análise energética, o perfil de utilização de energia, a energia cultural líquida e a eficiência cultural do agroecossistema milho cultivado em assentamento rural do Estado de São Paulo, tendo como hipótese a utilização do modelo agrícola denominado produtivista, onde privilegia-se o uso intensivo de energia nãorenovável, em que pese a organização social da produção possuir caráter familiar, forma coletiva de percorrer o itinerário técnico e fundamentar-se numa política de democratização do acesso à terra...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The objective of agriculture is to produce food and raw material in which the energy used is fundamental. Cultures energy analysis is so important as the others, and is possibly the one that translates situations in a more structural form. Agroecosystems can be analyzed and expressed under the energy viewpoint, and the determination of indexes to evaluate them deserves special attention, since the culture technical itinerary related to energy use defines levels of dependence with certain productive systems. From the energy point of view, bottlenecks of difficult surpass are not recommended and the energy analysis, when determining indexes that relate energy input and output, is justified as a complementary tool of evaluation. It was observed the high importance of corn culture in Brazilian agriculture, specially at rural settlements, and its participation in different ways of production social organization, including family agriculture, the significant demand for land in Brazil with relative abundance of labor force, and the different technical itineraries traversed until the final production of grain. The present work aimed to determine through energy analysis the outline of energy use, the culture efficacy and the culture net energy of the agroecosystem corn grown in rural settlement in São Paulo State, having as hypothesis the use of productivist agricultural model, where the intensive use of non-renewable energy is privileged, in which the familiar production character, collective way to traverse the technical itinerary and the politics of democratization of land access are considered. From studies which established the most varied energy indicators, the methodology used was based on coefficients better adjusted to the reality. ...(Complete abstract, click electronic access below) / Doutor

Une recrudescence de l’émergence ou de la réémergence de maladies infectieuses touchant l’homme ou ses animaux domestiques a été constatée ces dernières décennies. La majorité de ces maladies sont zoonotiques, c’est à dire originaires de la faune sauvage, et impliquent souvent un vecteur dans leur cycle de transmission. Parallèlement, des changements d’utilisation du sol en lien avec une intensification agricole modifient les paysages. L’objectif de cette thèse était d’améliorer l’état des connaissances de l’influence du paysage sur les relations entre hôtes, vecteurs et pathogènes. En Europe, les micromammifères peuvent abonder dans la plupart des écosystèmes terrestres, ce qui en fait des hôtes de choix pour les tiques généralistes Ixodes ricinus. Ils sont aussi des réservoirs d’agents infectieux transmis par les tiques. Les résultats de la thèse sont basés sur deux ans d’échantillonnage, printemps et automne, des micromammifères et des tiques dans différents paysages. Nous avons aussi recherché trois agents infectieux qu’ils hébergent et transmettent : Borrelia burgdorferi sensu lato (maladie de Lyme), Anaplasma phagocytophylum (anaplasmose) et Theileria (Babesia) microti (piroplasmose), ce dernier n’ayant pu être exploité en raison de sa trop faible prévalence. Les 24 sites d’échantillonnage étaient pour moitié en cœur ou en lisière de forêt et pour moitié dans des paysages agricoles offrant un gradient d’occupation du sol et d’ouverture du paysage. Le meilleur facteur explicatif de l’abondance de nymphes est la présence de larves d’I. ricinus l’année précédente. Les résultats indiquent aussi une relation entre le nombre de larves portées par les mulots sylvestres (Apodemus sylvaticus ; 76,5% des captures) et l’abondance de nymphes l’année suivante. Les campagnols roussâtres (Myodes glareolus ; 22,3% des captures) portaient moins de larves au printemps, certainement du fait d’une résistance acquise aux tiques des individus hivernants. Bien que ces deux espèces réagissent différemment aux variables de composition et de configuration du paysage, les abondances de nymphes n’étaient pas expliquées par ces variables. D’autres hôtes, comme les chevreuils (Capreolus capreolus), et des facteurs microclimatiques et météorologiques influencent donc probablement aussi les abondances et la distribution des tiques dans le paysage. La richesse spécifique des hôtes et l’abondance des campagnols roussâtres, trois fois plus infectés que les mulots sylvestres, amplifieraient les prévalences d’A. phagocytophylum de ces deux espèces de rongeurs. A l’inverse, la fragmentation du paysage, via la réduction de la taille des populations d’hôtes, semble agir négativement sur ces prévalences. Aucun patron spatial évident n’a été observé pour B. burgdorferi s.l.. De même, aucun lien n’a pu être fait entre les prévalences des rongeurs et celles des nymphes d’I. ricinus. Ces résultats suggèrent un rôle probable d’espèces de tiques plus spécialistes, I. trianguliceps et I. acuminatus, dans la circulation des agents infectieux étudiés, soulignant l’intérêt qu’il pourrait y avoir à considérer l’ensemble de la communauté de vecteurs dans de futures études. L’ensemble des résultats soulignent aussi l’importance qu’il y aurait à considérer un maximum d’hôtes micromammifères réservoirs, même peu abondants, à l’échelle du paysage pour mieux comprendre la transmission de ces maladies infectieuses vectorielles. / An increase in the emergence or in the reemergence of infectious diseases of human and his domestic animals has been observed in the last decades. Most of these diseases are zoonotic, i.e. originated from wildlife, and imply often a vector for their transmission. At the same time, land use changes linked to agricultural intensification have modified the landscapes. The aim of the thesis was to enhance the state of knowledge on the influence of the landscape on the relationships between hosts, vectors and pathogens. In Europe, small mammals can be abundant in most of terrestrial ecosystems; they are thus preferred hosts for the generalist tick species Ixodes ricinus. They are also reservoirs of tick-borne infectious agents. The results of this thesis are based on two years of sampling, in spring and autumn, of small mammals and ticks in different landscapes. We analyzed them for three of the infectious agents they host and transmit: Borrelia burgdorferi sensu lato (Lyme disease), Anaplasma phagocytophylum (anaplasmosis) and Theileria (Babesia) microti (piroplasmosis), this last one could not be exploited because of too low prevalence. The 24 sampling sites were half in the core or the edge of a forest and half in agricultural landscapes with a gradient of land cover and of landscape openness. The best explanatory variable for nymph abundance was the presence of I. ricinus larvae the previous year. The results also indicate a relationship between the number of larvae attached on wood mice (Apodemus sylvaticus ; 76,5% of the catches) and the abundance of nymphs the following year. Bank voles (Myodes glareolus ; 22,3% of the catches) harbored less larvae in spring, certainly because of an acquired resistance to ticks in the overwintering individuals. Despite that these two species react differently to the composition and configuration features of the landscape, the abundances of nymphs were not related to these features. Other hosts, like roe deer (Capreolus capreolus), meteorological and microclimatic factors probably influence the abundances and the distribution of ticks in the landscape. The host specific richness and the abundance of bank voles, which were threefold more infected than wood mice, likely amplified the prevalence of A. phagocytophylum of these two rodent species. Conversely, landscape fragmentation, via the reduction of host population sizes, seems to act negatively on this prevalence. No clear spatial pattern was observed for B. burgdorferi s.l.. Likewise, no link could be established between the prevalence of the rodents and the prevalence of the nymphs. These results suggest a possible role of more specialist tick species, I. trianguliceps and I. acuminatus, in the circulation of the studied infectious agents, emphasizing the possible interest of considering the whole vector community in further studies. The results also emphasize the importance of considering a maximum of small mammal reservoir hosts, even at low abundances, at the landscape scale to better understand the transmission of these vector-borne infectious diseases.