Seasonal variability in leaf and whole-tree responses of Populus tremula L. to elevated CO2 and drought

Trees are exposed to unprecedented climate change, characterized by rapidly rising atmospheric CO2 concentration and longer and more intense drought episodes. Despite research efforts to predict effects of elevated CO2 (eCO2) on tree functioning, its temporal and spatial variability and the interaction between eCO2 and drought remain intensely debated. To address these knowledge gaps, this PhD dissertation investigates the effects of eCO2 on one-year-old European aspen trees at the beginning and the end of the growing season, and under well-watered and drought conditions. For this, leaf and whole-tree water use, carbon gain and carbon loss were monitored during two consecutive growing seasons under ambient or elevated atmospheric CO2 concentration. The conducted literature review and experiments highlight three important insights. First, the magnitude of the effects of eCO2 is highly variable over time, even within a single growing season, as a likely result of the different seasonal carbon requirements throughout plant development. Second, tree responses to eCO2 should not be derived from observations made at the leaf level. Finally, the alleviating effects of eCO2 when facing drought were limited to the leaf level and the late season in European aspen, suggesting a negligible role of CO2 fertilization in mitigating detrimental effects of drought

Predictions of angle dependent tortuosity and elasticity effects on sound propagation in cancellous bone

The anisotropic pore structure and elasticity of cancellous bone cause wave speeds and attenuation in cancellous bone to vary with angle. Previously published predictions of the variation in wave speed with angle are reviewed. Predictions that allow tortuosity to be angle dependent but assume isotropic elasticity compare well with available data on wave speeds at large angles but less well for small angles near the normal to the trabeculae. Claims for predictions that only include angle-dependence in elasticity are found to be misleading. Audio-frequency data obtained at audio-frequencies in air-filled bone replicas are used to derive an empirical expression for the angle-and porosity-dependence of tortuosity. Predictions that allow for either angle dependent tortuosity or angle dependent elasticity or both are compared with existing data for all angles and porosities

Acoustic response of a rigid frame porous medium slab with a periodic set of inclusions

The acoustic response of a rigid frame porous slab with a periodic set of inclusions is calculated by use of a multipole method. The acoustic properties, in particular the absorption, of such a structure are then derived and studied. Numerical results together with a modal analysis show that the addition of a periodic set of high-contrast inclusions leads to quasi-modes excitation of both the slab and the gratings, and to a large increase of the acoustic absorption of the initial slab, this being partly due to the quasi-modes excitation.Comment: submitted to Journal of Sound and Vibratio

Simulation of long-term stem diameter variation of Ficus benjamina based on simulated transpiration

Greenhouse microclimate (light, temperature, relative humidity and CO2) and irrigation are important factors for plant growth, development and quality in ornamental horticulture. To optimize plant growth, actual stem diameter growth can be measured and compared with a desired growth pattern. Using the deviation between measured and simulated stem diameter growth, growers can decide whether and in which way the microclimate or irrigation needs to be adjusted. Together with this decision, costs associated with climate control and irrigation must also be taken into account. This will help growers to find a proper balance between cultivation costs and plant growth. In this study, Ficus benjamina was grown from cutting to mature plant in a controlled greenhouse environment. Growing conditions, microclimate as well as plant spacing, closely resembled the ones used in commercial greenhouses. Microclimate, soil water content, leaf temperature, sap flow, stem diameter variation and leaf thickness were continuously measured on three plants. In addition, discrete measurements of leaf area, projected crown surface area, stem water potential, photosynthesis, transpiration and stomatal conductance were performed. These measurements were used to further extend a mechanistic plant model, which allows simulation of long-term stem diameter variation

Materials Testing

International audienceIn recent years, a number of models to calculate the acoustical behaviour of porous materials (sound absorption, sound insulation and vibration damping) have been developed [1]. Although these models are based on physical sound theories, they require a number of material parameters and the output of a calculation will depend on the accuracy of the input parameters. Depending on the complexity of the porous material and the configuration to be modeled, up to seven parameters may be needed

Use of leaf thickness sensors in horticultural crops

Changes in leaf thickness can be a rapid indicator of the plant’s water status and can therefore serve as an alarm signal for potential water deficits. Combining the use of continuous leaf thickness measurements with a mechanistic plant model describing optimal leaf growth and diel variations, would allow growers to optimize greenhouse growing conditions by adaptation of the microclimate and applied irrigation. Recent development of new sensors offers the possibility for real time measurements of leaf thickness on small plants, including ornamentals. However, the accuracy of leaf thickness variation measurements needs to be assured. In this study, the temperature influence on 12 LeafSen (Netafim, Tel Aviv, Israel) sensors has been tested in a temperature range from 16 °C to 31 °C by installation of the sensors on aluminium plates. Temperature variations in the investigated range resulted in sensor signal differences of up to 48 μm, indicating that temperature response can exceed the expected diel leaf thickness variation. Two typical temperature responses were distinguished, pointing to the need for a sensor specific temperature correction. The practical use of leaf thickness sensors and the established temperature corrections has been demonstrated by installing the sensors on the stem and leaf of three Ficus plants (Ficus benjamina) and three pot roses (Rosa chinensis cv.) starting from cutting stage in a commercial greenhouse environment

Contribution of the glass cladding to the overall structural behaviour of 19th-century iron and glass roofs

In the 19th-century architecture, the use of iron and glass roofs made it possible to bring light to the core of buildings. Together with the social context of the Industrial Revolution and the improvements in heating techniques, the creation of a “Garden of Eden” became popular. Building typologies like railway stations, market halls, fabrication halls, exhibition halls and greenhouses exploited this possibility at full extend. When renovating the 19th-century iron and glass roofs, both the heritage value and modern standards on safety and structural performance have to be taken into account. A first part of the research, which is based on literature study, goes into the construction history of iron and glass roofs to define the heritage value of the roof (and its components) to be restored. The second part puts forward a methodology to recalculate the performance of the original structure by taking into account iron and glass. Lab tests were performed to deliver data that was still missing to do so. Tests on historic adhesives, namely putty, were carried out. And modern adhesives were applied on elements that show effects of deterioration, present in renovation projects. Finally, a parameter study was carried out to determine the effect of renovation options which are applied nowadays: replacing historic putty by modern adhesives, replacing single glass by laminated glass, etc. Simulations showed that taking in account the original single glass panels in a calculation (even when connected with putty), has a positive impact on the overall behaviour

Characterization of porous acoustic materials

International audienceAn overview of the models and parameters of the acoustic wave propagation in porous media is presented. The most common parameters (the porosity, the permeability or flow resistivity and the densities) can be measured with standard methods. Ultrasonic methods for measuring the other parameters (the tortuosity and characteristic lengths) related to the complex pore micro-structure are reviewed. The ultrasonic methods are based on the transmission or reflection of airborne ultrasonic waves and on the signal analysis in the frequency and/or in the time domains. Ultrasonic scattering is discussed at higher frequencies where the classical models are no longer valid. In order to complete the characterization of porous acoustic materials, new techniques for evaluating the elastic and viscoelastic properties are proposed. These techniques are based on the generation of standing waves in a layer of material and on the spatial Fourier Transform of the displacement profile of the upper surface. Two configurations are proposed: a layer of porous material glued on a rigid substrate and a porous layer under Lamb conditions. Theoretical dispersion curves are fitted to the experimental results and this procedure can provide information on the complex shear modulus and of the complex Poisson ratio in a wide frequency range, typically between 50 Hz and 4 kHz