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We examined the effects of periodic nitrogen (N) and phosphorus (P) fertilizer applications on the O horizon and mineral soil in loblolly pine (Pinus taeda L.) plantations over a 12-year period. To accomplish this, we used 9 experimental sites located across the south, which were grouped using the CRIFF Classification System. Group 1—CRIFF A, B (poorly-drained Ultisols); group 2—CRIFF C, D, G (sandy Spodosols and Entisols); and group 3—CRIFF E, F (well-drained Ultisols). Fertilization rates were 135, 202, and 269 kg N ha-1 at 4 years application frequency. This resulted in a cumulative N application rate of 540, 808, and 1076 kg ha-1. P was added at 10% of the N rate. Fertilization increased the mass, N content, and P content of the O horizon in all soil groups. Fertilization did not impact mineral soil N. No significant increases in total N trends were observed to a depth of 1 m. Likewise, total inorganic N (NH4+ + NO3-) was not affected by fertilization. These results suggest that N fertilization will have little effect on long-term soil N availability regardless of soil types. In contrast, fertilization increased extractable P in soil CRIFF groups 1, 2, and 3 by 26, 60, and 4 kg P ha-1 respectively suggesting potential for long-term soil P availability and site quality improvement. However, the low extractable P in soil group 3 implies additional fertilization with P for the next rotation for sites included into this soil group. / Master of Science

Plants adapt genetically and phenotypically to abiotic and biotic environmental conditions, and associated changes in their traits and investment strategies may affect their palatability to herbivores. This study aims to investigate if ecosystem retrogression results in heritable adaptation of Betula pubescens and how this impacts seedling growth, response to fertilizer, and palatability to the herbivore Spodoptera littoralis. Seeds were collected from a retrogressive island chronosequence for which nutrient availability increased with island size. Seeds were grown in a common garden and a fertilizer experiment was carried out to analyze genetic and phenotypic adaptations to nutrient availability. A bioassay using S. littoralis larvae was conducted to reveal the effect of adaptations to nutrient availability and herbivory on plant palatability. Only the root-to-shoot ratio indicated any heritable adaptation, being higher for seedlings originating from small islands. Seedlings showed highly plastic responses to fertilizer, indicative of an increased acquisition of resources. The palatability of B. pubescens was mainly determined by a tradeoff between leaf dry matter content and specific leaf area and was reduced by induced defenses. The acquisition of resources, growth, and reproduction of B. pubescens appears to be driven largely by phenotypic plasticity rather than prior genetic adaptation. Since all treatment responses were independent of island size, the whole population may be resilient to future changes in environmental conditions. The study revealed that ecosystem retrogression does not have to result in heritable plant adaptations, even if changes in ecosystem conditions can be substantial. It is of great importance to gain more knowledge on how species may adapt to future changes in environmental conditions over different timescales, both to naturally and anthropogenically induced changes.

Root system development in the early phases of plant ontogeny Seed germination and subsequential developement of the root system is a critical stage of life of a newly rising plant. The plant must recognise and suitably and quickly find an answer to the environmental conditions in which it finds itself. However, the way in which the root system develops and its final architecture depends not only on the environmental conditions but also on the plant itself. In addition, responses to different conditions may vary among different plant species. This work examines the developement of a root system in the first four weeks of a plant's life. It observes the dependence on the amount of available nutrients in the substrate and on the amount of available nutrients the seed is given by the mother plant. It also briefly touches on the relations between seed germination, seed size and the amount of available nutrients. No differences relating to the amount of available nutrients were found in seed germination. However, differences in germination speeds were found between plant species. Plant biomass increases with the increasing amount of available nutrients in the substrate. This increase is relatively greater for plant species with a small seed size. Plant species with a big seed size invest relatively more...

All natural aquatic systems harbour a vast variety of microorganisms. In the aquatic microbial food web, the larger microorganisms (i.e. protozoa) feed on the smaller microorganisms (i.e. bacteria and phytoplankton). An increase in nutrient availability results in changes of the microbial food web structure, like altered community composition and blooms of toxic phytoplankton. In this thesis work I hypothesised that nutrient-rich aquatic environments, with strong protozoan predation, favour the occurrence of predation-resistant bacteria like F. tularensis, and that the microbial food web may provide a reservoir for the bacterium between outbreaks. By using a size-structured ecosystem food web model it was shown that the protozoan predation pressure on bacteria, defined as protozoan predation per bacterial biomass, increases with increasing nutrient availability in aquatic systems (estimated chlorophyll a 0.2 to 112 μg L-1). This dynamics was caused by increasing growth-rate of a relatively constant number of bacterial cells, maintaining the growth of an increasing number of protozoan cells. The results were supported by meta-analysis of field studies. Thus my results suggest that protozoa control the bacterial community by predation in nutrient-rich environments. In a field study in a natural productivity gradient (chlorophyll a 1.4 to 31 μg L-1) it was shown that intense selection pressure from protozoan predators, favours predation-resistant forms of bacteria. Thus, the abundance of predation-resistant bacteria increases with increasing nutrient availability in lakes. Furthermore, I could demonstrate that the bacterium Francisella tularensis, the causative agent of tularemia, was present in eutrophic aquatic systems in an emerging tularemia area. Isolated strains of the bacterium were found to be resistant to protozoan predation. In a microcosm study, using natural lake water, high nutrient availability in combination with high abundance of a small colourless flagellate predator favoured the occurrence of F. tularensis holarctica. In laboratory experiments F. tularensis strains were able to form biofilm at temperatures between 30-37°C, but not below 30°C. In conclusion, I have shown that the protozoan predation pressure on bacteria increases with increasing nutrient availability in aquatic systems. Predation-resistant forms of bacteria, such as F. tularensis are favoured in nutrient-rich environments. The complexity of the microbial food web and nutrient-richness of the water, influence the transmission of the pathogenic F. tularensis holarctica. However, over long periods of time, the bacterium survives in lake water but may lose its virulence. The temperature-regulated biofilm formation by F. tularensis may play a role in colonization of vectors or for colonization of hosts, rather than for survival in aquatic environments.

No description available.

High-biomass cover cropping enhances marketable yields in organic production of vegetables, linked to the improvement of soil quality and weed control. Although, during transition from chemical to organic cover-cropping production, especially with no-till systems, reduction of nitrogen availability to the main crop and increase in weed and pest pressure may occur. In 2004-2005, summer and fall broccoli (Brassica oleraceae L. Botrytis Group) crops were grown in twin rows on permanent (controlled traffic) raised beds (185-cm wide). Before broccoli transplanting, high-biomass cover crops were grown in specific bed areas. Legumes (Vicia villosa, Glycine max L., and Crotolaria juncea L.) on bed tops (grow zones) and grass species (Secale Cereale L., Setaria italica L., and Sorghum bicolor X S. bicolor var. Sudanese) in the alleyways (bed shoulders and bottoms). Experimental treatments were tillage (conventional, CT; and no-tillage, NT), farmscaping (with and without), and nitrogen sidedressing (with and without, applied 3 weeks after transplanting as a mixture of sodium nitrate - 22 kg N ha-1 - and feathermeal - 44 kg N ha-1). Weeds were managed by mechanical cultivation in CT and a spot weeding by hand in NT treatments. High numbers of beneficial insects (Cotesia glomerata, Cotesia orobenae and Diadegma insulare) kept the primary insect pest population (Pieris rapae, Evergestis rimosalis (Guenee), and Plutella xylostella) at a pest to predator ratio below 4:1. Although the excellent insect pest control was attributed to the farmscape plantings, pest level and crop yields were not significantly affected by farmscaping (likely due to the close proximity of the farmscaped plots (10-50m from non-farmscaped)). Broccoli yield averaged 62% higher in fall than summer (12.1 vs. 7.5 t ha-1) likely due to cool weather conditions during broccoli head development (October), increasing head size, uniformity, and marketability. In 2004, broccoli yield in CT plots was either equal or slightly higher than NT (9.5 vs. 9.0 t ha-1). However, in 2005, broccoli yield in CT plots was significantly higher in both spring (8.8 vs. 6.8 t ha-1; p = 0.0258) and fall crops (13.5 vs. 12.3 t ha-1 with p = 0.0484). Nitrogen sidedressing improved yield in all plots (9.8. vs. 12.7 t ha-1) and particularly in NT (8.6 vs. 12.1 t ha-1), indicating that availability and/or synchrony of nitrogen was a limiting factor. Incorporating high-N legume residues in the grow zones resulted in a lesser N response in CT. / Master of Science

Reindeer appear to have strong positive effects on plant productivity and nutrient cycling in strongly nutrient-limited ecosystems. While the direct effects of grazing on vegetation composition have been intensively studied, much less is known about the indirect effect of grazing on plant-soil interactions. This thesis investigated the indirect effects of ungulate grazing on arctic plant communities via soil nutrient availability and plant nutrient uptake. At high density, the deposition of dung alone increased plant productivity both in nutrient rich and nutrient poor tundra habitats without causing major changes in soil possesses. Plant community responses to dung addition was slow, with a delay of at least some years. By contrast, a 15N-urea tracer study revealed that nutrients from reindeer urine could be rapidly incorporated into arctic plant tissues. Soil and microbial N pools only sequestered small proportions of the tracer. This thesis therefore suggests a strong effect of dung and urine on plant productivity by directly providing nutrient-rich resources, rather than by stimulating soil microbial activities, N mineralization and ultimately increasing soil nutrient availability. Further, defoliation alone did not induce compensatory growth, but resulted in plants with higher nutrient contents. This grazing-induced increase in plant quality could drive the high N cycling in arctic secondary grasslands by providing litter of a better quality to the belowground system and thus increase organic matter decomposition and enhance soil nutrient availability. Finally, a 15N natural abundance study revealed that intense reindeer grazing influences how plants are taking up their nutrients and thus decreased plant N partitioning among coexisting plant species. Taken together these results demonstrate the central role of dung and urine and grazing-induced changes in plant quality for plant productivity. Soil nutrient concentrations alone do not reveal nutrient availability for plants since reindeer have a strong influence on how plants are taking up their nutrients. This thesis highlights that both direct and indirect effects of reindeer grazing are strong determinants of tundra ecosystem functioning. Therefore, their complex influence on the aboveground and belowground linkages should be integrated in future work on tundra ecosystem N dynamic.

Ce travail s'inscrit dans le cadre du projet OUTPACE visant à caractériser les eaux du Pacifique tropical Sud-Ouest (WTSP) en termes de stocks et flux biogéochimiques, et de diversité biologique des diazotrophes le long d'un transect longitudinal Ouest-Est. Il est le fruit de la combinaison étroite de deux approches, l'une expérimentale et l'autre basée sur la modélisation, dans le but d'étudier le rôle de la diazotrophie dans la dynamique planctonique et les cycles biogéochimiques des eaux de surface du WTSP. Les analyses de plusieurs grandeurs mesurées lors de la campagne, et notamment la production primaire (PP) et du temps de turnover du phosphate inorganique dissous (DIP), ont permis d'observer un gradient Ouest-Est de productivité et de disponibilité nutritive, étroitement lié à la variabilité spatiale des taux de fixation de N$_2$. L'utilisation d'un modèle biogéochimique mécaniste (implémenté dans la plateforme Eco3M) incluant explicitement deux compartiments de diazotrophes, couplé à un modèle physique 1D vertical, a permis de mettre en évidence le fait que l'absence/présence de diazotrophie permettait d'expliquer le contraste observé entre les régions de l'Ouest de l'archipel Mélanésien (WMA) et de l'Ouest de la gyre du Pacifique Sud (WGY). Les résultats du modèle ont montré que les organismes non diazotrophes bénéficiaient de l'apport d'azote nouveau apporté par la fixation de N$_2$, et que la production planctonique de surface dépendait significativement de l'activité des diazotrophes, cette dernière contrôlée à l'Ouest par la disponibilité en phosphate et à l'Est par la disponibilité en fer. / This work is part of the OUTPACE project which aimed to characterize the western tropical south Pacific (WTSP) in terms of biogeochemical stocks and fluxes and biological diversity of diazotrophs along a West-East longitudinal transect. This work combines an experimental with a modeling approach in order to study the role of diazotrophy in the planktonic dynamics and biogeochemical cycles of the WTSP surface waters. The values measured during the campaign, iespecially those of primary production (PP) and dissolved inorganic phosphate (DIP) turnover time, revealed a West-East gradient of productivity and nutrient availability, closely related to the spatial variability of N$_2$ fixation rates. The use of a mechanistic biogeochemical model (implemented in the Eco3M platform) explicitly including two compartments of diazotrophs and coupled with a vertical 1D physical model, allowed to highlight the fact that the absence / presence of diazotrophy could explain the contrast between the western regions of the Melanesian Archipelago (WMA) and the west of the south Pacific gyre (WGY). ). The model results showed that non-diazotrophic organisms benefited from the new nitrogen supply provided by nitrogen fixers, and that the surface planktonic production depended significantly on diazotroph activity, which is controlled by the phosphate availability in the west and by the iron availability in the east of the WTSP.