254 research outputs found

    Plant-soil interaction and soil carbon turnover across geochemical and topographic gradients in African tropical montane forests

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    Tropical forests play a central role in global carbon (C) cycles due to the high exchange rate of carbon between plants, soil, and the atmosphere. Nutrient availability in tropical forest systems controls these exchanges via their impact on tree growth, carbon productivity, and stocks. Research shows that local edaphic factors such as soil parent material and topography codetermine nutrient availability. However, the process knowledge of how tropical forests respond to changes in nutrients, the chemistry of the local parent material and topography, and the effect this has on C cycling between plants, soils, and the atmosphere remains unclear. This gap in knowledge obstructs the mechanistic understanding of the controls of C cycling in tropical forest systems. Furthermore, data for African tropical forests are scarce, as most research has focused mainly on Amazon and South Asia. This thesis tried to answer these questions and provided directions on where future research can focus. This thesis is based on both experimental (field and laboratory) and observational studies at different sites in the Eastern Congo Basin and along the Albertine Rift Valley System. It has three major parts: (a) nutrient uptake and distribution in the canopy of African tropical forests, (b) C stocks, Net Primary Productivity (NPP), and NPP C allocation between plant compartments, and (c) soil potential heterotrophic respiration (SPR) and soil organic carbon (SOC) turnover rate in forests developed along geochemical and topographic gradients. Specifically, the thesis focused on three contrasting geochemical regions (mafic magmatic, felsic metamorphic, and a mixture of sedimentary rock but distinct from mafic and felsic. Throughout the thesis, the three regions are referred to as “mafic”, “felsic”, and “sedimentary). Chapter 2 assessed canopy chemistry of 344 samples collected from different tree species growing on different parent materials and topographic positions. The data shows that tropical forest canopy chemistry shifts significantly when local soils and parent material geochemistry indicate fertility constraints, mainly due to low amounts of rock-derived nutrients. In contrast, topography did not affect canopy chemistry in the three investigated geochemical regions. Chapter 3 assessed the effects that soil parent material and topography as drivers of soil fertility have on forest NPP, C allocation, and biomass C stocks and how they relate to SOC stocks. Here a combination of two years monitoring of vegetation growth and soil geochemical properties measurements were used. The thesis found that soil fertility parameters reflecting the local parent material are the main drivers of NPP and C allocation patterns in tropical montane forests, resulting in significant differences in below to aboveground biomass ratio across geochemical regions. Topography did not constrain the variability in C allocation and NPP. Furthermore, SOC stocks showed no relation to C input in tropical forests. Instead, plant C input seemingly exceeded the maximum potential of these soils to stabilize C. Chapter 4 assessed potential heterotrophic soil respiration and SOC turnover via lab-based incubation experiments. Here, depth explicit SPR and Δ14C of samples originating from the three geochemical regions and topographic positions were measured under constant temperature and moisture conditions. The results revealed distinct patterns in soil respiration with soil depth and parent material geochemistry. The topographic origin of the samples was not the main determinant of the observed respiration rates and Δ14C. However, in situ soil hydrological conditions likely influence soil C turnover by inhibiting decomposition in valley subsoils. Overall, the results of this thesis demonstrate that, even in deeply weathered tropical soils, parent material has a long-lasting effect on soil geochemistry that can affect (1) nutrient availability, and uptake, (2) NPP, and C allocation, ultimately affecting differently above and belowground biomass, (3) microbial activity, the size of subsoil C stocks and the turnover rate of C in soil. Therefore, soil parent material and its control on soil chemistry need to be taken into account to predict C fluxes and to understand C cycling in African old-growth tropical forest systems

    Differential Migration Timing and the Form and Function of Avian Wings

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    A common differential migration strategy in birds is protandry, whereby males arrive earlier than females. The probable causes of protandry are well studied from the perspective of innate and physical environmental cues, but the influence of the social environment and wing morphology are less known. Theoretical models propose that sex ratio influences protandry; male-biased sex ratios are predicted to advance timing in males due to increased intrasexual competition. To empirically test this, I investigated the spring migration traits of male Yellow-rumped Warblers Setophaga coronata under differing sex ratios. An integrated automated telemetry approach was used, where locomotor movement of captive birds was quantified, followed by the use of Motus Wildlife Tracking System to quantify stopover departure timing post release. Males from the female-biased environment exhibited more locomotor movement and had an earlier onset of migratory restlessness, a proxy for the urge to migrate, suggesting that the composition of the social environment can influence migration behaviour. Next, I assessed the relationship between wing morphology and both differential arrival timing and flight performance in migratory passerines, as pointed wings are theorized to aid level-flight efficiency and impede take-off performance. A long-term migration monitoring dataset revealed that protandry and sexual size dimorphism of wing length co-vary by age, which is believed to reflect a coevolutionary response to sexual selection and viability selection. Larger males may be better able to afford the viability costs of early arrival and younger males may reduce competition with older males by arriving later. Wingtip morphology was characterized using the feather length measurements of 1929 individuals from 18 families and a flight tower was used to determine whether these morphologies influence take-off flight performance. Males, with larger and more convex wingtips, exhibited faster take-off speeds than females. Although older birds had more pointed wingtips than younger birds, this trait did not impact take-off speed. Overall, these findings suggest that males and older birds have competitive advantages and are likely better at escaping predation. Understanding the probable causes of differential migration provides insights on the basic knowledge of avian migration and helps to predict the consequences of future climate change

    A Techno-Economic Assessment of Shipping Through the Arctic

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    The Arctic Ocean is experiencing considerable and adverse environmental change driven by global warming. Global warming is inducing Arctic ice to melt and recede, facilitating increased accessibility for ships to transit through. Arctic shipping routes are shorter than their counterparts the Suez and Panama Canal routes. For the same origin and destination, a shorter shipping route would enable lower transport costs and an increased volume of trade. In this thesis, the principal contribution is to expand the framing of Arctic shipping feasibility to include costs from emission externalities and assess Arctic shipping feasibility on balance with these externalities. Five scenarios which represent different societal choices and levels of global warming were considered to see how they affect the development of Arctic shipping viability. All ships are treated as newbuilds, alternative fuelled ships are assumed to have the machinery retrofitted on top of the newbuild design. A dimensionless metric was proposed to enable a comparison of Arctic shipping feasibility between the different scenarios in the years 2020, 2035 and 2050. Including emission damages increased the feasibility of Arctic shipping due to the lower damages associated with air pollution in the Arctic and a lower intensity of emissions. However, only externalities from a select number of emission species were considered which means that the considered environmental costs are an underestimate. The veracity of increased feasibility is discussed. A deterministic analysis was complemented with a stochastic assessment to address uncertainties and show that Arctic shipping probably becomes economically feasible for container shipping and infeasible for dry bulkers across all scenarios. Mixed results were returned for tankers. A sensitivity analysis found that the most significant variables that determine Arctic shipping feasibility were the cost of carbon, engine load and route lengths. This thesis concludes with a discussion on the implications of these results

    Is there lignin in the Ulva cell wall? A multidisciplinary structural investigation to provide new insights into cell wall evolution and macroscopic complexity in the chlorophyte green seaweeds

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    Seaweeds are not only an integral component of the marine ecosystem via their role in global carbon and sulfur cycles, but also have significant economic value as crops for food and fuel, with certain intertidal seaweeds like the green 'sea lettuce' Ulva (Chlorophyta) appearing as attractive bioenergy feedstocks due to their rapid growth rates and polysaccharide-rich cell wall that can comprise half its total biomass. Seaweeds have a distinct biochemistry to traditional land plant crops. For example, they lack the phenylpropanoid pathway, a key milestone in land plant evolution that enabled the biosynthesis of the secondary cell wall biopolymer lignin which confers structural support and facilitates water transport in vascular plants. Despite this, 'lignin-like' fractions are reported in Ulva, and lignin has been found in a coralline red seaweed (Rhodophyta). No alternative pathway for lignin biosynthesis is provided by our current metabolic knowledge, meaning we have limited understanding of how ‘lignin’ arose in seaweeds. Furthermore, the only comprehensive structural investigation into seaweed 'phycolignin' to date has been performed in the coralline reds. Consequently, the presence of an equivalent component in green seaweeds like Ulva is still debatable. As the primary aim of this thesis, I investigate the identity of the proposed lignin-like fraction of Ulva using confocal microscopy, biochemical assays, and biophysical analysis. To accomplish this, I evaluate the use of a sequential extraction protocol described for charophyte green algae (Streptophyta) to determine which cell wall polysaccharides the proposed structure associates with. No evidence for lignin-like structures in the Ulva cell wall was identified during this research. Instead, I propose that the previous attributions to lignin in Ulva were misidentifications on account of the limitations of quantification protocols used. Interestingly, a major structural protein component is identified with possible implications for how Ulva mitigates osmotic stress at low tide. The absence of 'phycolignin' in the Ulva cell wall contrary to the lignified coralline seaweeds demonstrates that seaweeds display diverse adaptations to intertidal habitats, and provides support to the current hypothesis that lignin arose convergently in the red lineage, with green seaweeds and land plants sharing a more recent evolutionary history

    ECOS 2012

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    The 8-volume set contains the Proceedings of the 25th ECOS 2012 International Conference, Perugia, Italy, June 26th to June 29th, 2012. ECOS is an acronym for Efficiency, Cost, Optimization and Simulation (of energy conversion systems and processes), summarizing the topics covered in ECOS: Thermodynamics, Heat and Mass Transfer, Exergy and Second Law Analysis, Process Integration and Heat Exchanger Networks, Fluid Dynamics and Power Plant Components, Fuel Cells, Simulation of Energy Conversion Systems, Renewable Energies, Thermo-Economic Analysis and Optimisation, Combustion, Chemical Reactors, Carbon Capture and Sequestration, Building/Urban/Complex Energy Systems, Water Desalination and Use of Water Resources, Energy Systems- Environmental and Sustainability Issues, System Operation/ Control/Diagnosis and Prognosis, Industrial Ecology

    Environmental Hydraulics Research

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    This book aims to provide research and engineering applications related to water and hydraulic problems. It is comprised of scientific papers in all topics of hydraulics, in particular, on sustainable water management, environmental hydraulics, ecohydraulics, water–energy nexus, and systems protection and efficiency. Safety and innovation issues, interdisciplinary problems, and linkage of theory to experimental and field applications can also be found within. Solutions of water problems in the form of prediction models, flow simulations, engineering systems, monitoring, management strategies covering scientific investigations and/or experimental or field studies of flow behaviour, hydrodynamics, and climate changes effects and adaptation, new design solutions, innovative approaches in the field of environment, hydraulics, techniques, methods, and analyses to address the new challenges in environmental hydraulics are alo presented and explored. This topic is studied both from a technical and environmental point of view, with the objective of protecting and enhancing the quality of the environment. In a cross-disciplinary field of study, this book comprises open channel/river flows and pressurised systems, combining, among others, new technological, social, and environmental hydraulic challenges, working in water-related fields with available information, new concepts and tools, new design solutions, eco-friendly technologies, and the advanced materials necessary to address the increasing challenges of ensuring a sustainable water environment by promoting the adaptation, flexibility, integration, and sustainability of recognised environmental solutions

    Comparative Analysis of Student Learning: Technical, Methodological and Result Assessing of PISA-OECD and INVALSI-Italian Systems .

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    PISA is the most extensive international survey promoted by the OECD in the field of education, which measures the skills of fifteen-year-old students from more than 80 participating countries every three years. INVALSI are written tests carried out every year by all Italian students in some key moments of the school cycle, to evaluate the levels of some fundamental skills in Italian, Mathematics and English. Our comparison is made up to 2018, the last year of the PISA-OECD survey, even if INVALSI was carried out for the last edition in 2022. Our analysis focuses attention on the common part of the reference populations, which are the 15-year-old students of the 2nd class of secondary schools of II degree, where both sources give a similar picture of the students
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