Salinity Effect on Horticultural Crops: Morphological, Physiological, and Biomolecular Elements of Salinity Stress Response

Among abiotic stresses, high salinity stress is the most severe environmental stress. High salinity exerts its negative impact mainly by disrupting the ionic and osmotic equilibrium of the cell. In saline soils, high levels of sodium ions lead to plant growth inhibition and even death. Salt tolerance in plants is a multifarious phenomenon involving a variety of changes at molecular, organelle, cellular, tissue as well as whole plant level. In addition, salt tolerant plants show a range of adaptations not only in morphological or structural features but also in metabolic and physiological processes that enable them to survive under extreme saline environments. The main objectives of my dissertation were understanding the main physiological and biomolecular features of plant responses to salinity in different genotypes of horticultural crops that are belonging to different families Solanaceae (tomato) and Cucurbitaceae (melon) and Brassicaceae (cabbage and radish). Several aspects of crop responses to salinity have been addressed with the final aim of combining elements of functional stress response in plants by using several ways for the assessment of plant stress perception that ranging from destructive measurements (eg. leaf area, relative growth rate, leaf area index, and total plant fresh and dry weight), to physiological determinations (eg. stomatal conductance, leaf gas exchanges, water use efficiency, and leaf water relation), to the determination of metabolite accumulation in plant tissue (eg. Proline and protein) as well as evaluation the role of enzymatic antioxidant capacity assay in scavenging reactive oxygen species that have been generated under salinized condition, and finally assessing the gene induction and up-down regulation upon salinization (eg. SOS pathway).

Tuzla City (BiH): an example of geohazard induced by salt extraction

Salt deposits characterize the subsurface of Tuzla (BiH) and made it famous since the ancient times. Archeological discoveries demonstrate the presence of a Neolithic pile-dwelling settlement related to the existence of saltwater springs that contributed to make the most of the area a swampy ground. Since the Roman times, the town is reported as “the City of Salt deposits and Springs”; "tuz" is the Turkish word for salt, as the Ottomans renamed the settlement in the 15th century following their conquest of the medieval Bosnia (Donia and Fine, 1994). Natural brine springs were located everywhere and salt has been evaporated by means of hot charcoals since pre-Roman times. The ancient use of salt was just a small exploitation compared to the massive salt production carried out during the 20th century by means of classical mine methodologies and especially wild brine pumping. In the past salt extraction was practised tapping natural brine springs, while the modern technique consists in about 100 boreholes with pumps tapped to the natural underground brine runs, at an average depth of 400-500 m. The mining operation changed the hydrogeological conditions enabling the downward flow of fresh water causing additional salt dissolution. This process induced severe ground subsidence during the last 60 years reaching up to 10 meters of sinking in the most affected area. Stress and strain of the overlying rocks induced the formation of numerous fractures over a conspicuous area (3 Km2). Consequently serious damages occurred to buildings and infrastructures such as water supply system, sewage networks and power lines. Downtown urban life was compromised by the destruction of more than 2000 buildings that collapsed or needed to be demolished causing the resettlement of about 15000 inhabitants (Tatić, 1979). Recently salt extraction activities have been strongly reduced, but the underground water system is returning to his natural conditions, threatening the flooding of the most collapsed area. During the last 60 years local government developed a monitoring system of the phenomenon, collecting several data about geodetic measurements, amount of brine pumped, piezometry, lithostratigraphy, extension of the salt body and geotechnical parameters. A database was created within a scientific cooperation between the municipality of Tuzla and the city of Rotterdam (D.O.O. Mining Institute Tuzla, 2000). The scientific investigation presented in this dissertation has been financially supported by a cooperation project between the Municipality of Tuzla, The University of Bologna (CIRSA) and the Province of Ravenna. The University of Tuzla (RGGF) gave an important scientific support in particular about the geological and hydrogeological features. Subsidence damage resulting from evaporite dissolution generates substantial losses throughout the world, but the causes are only well understood in a few areas (Gutierrez et al., 2008). The subject of this study is the collapsing phenomenon occurring in Tuzla area with the aim to identify and quantify the several factors involved in the system and their correlations. Tuzla subsidence phenomenon can be defined as geohazard, which represents the consequence of an adverse combination of geological processes and ground conditions precipitated by human activity with the potential to cause harm (Rosenbaum and Culshaw, 2003). Where an hazard induces a risk to a vulnerable element, a risk management process is required. The single factors involved in the subsidence of Tuzla can be considered as hazards. The final objective of this dissertation represents a preliminary risk assessment procedure and guidelines, developed in order to quantify the buildings vulnerability in relation to the overall geohazard that affect the town. The historical available database, never fully processed, have been analyzed by means of geographic information systems and mathematical interpolators (PART I). Modern geomatic applications have been implemented to deeply investigate the most relevant hazards (PART II). In order to monitor and quantify the actual subsidence rates, geodetic GPS technologies have been implemented and 4 survey campaigns have been carried out once a year. Subsidence related fractures system has been identified by means of field surveys and mathematical interpretations of the sinking surface, called curvature analysis. The comparison of mapped and predicted fractures leaded to a better comprehension of the problem. Results confirmed the reliability of fractures identification using curvature analysis applied to sinking data instead of topographic or seismic data. Urban changes evolution has been reconstructed analyzing topographic maps and satellite imageries, identifying the most damaged areas. This part of the investigation was very important for the quantification of buildings vulnerability.

Salt stress responses in pear and quince: physiological and molecular aspects

The productivity of agricultural crops is seriously limited by salinity. This problem is rapidly increasing, particularly in irrigated lands. Like almost all the fruit tree species, Pyrus communis is generally considered a salt sensitive species, but only little information is available on its behavior under saline conditions. Previous studies, carried out in the Department of Fruit Tree and Woody Plant Science (University of Bologna), focused their attention on pear and quince salt stress responses to understand which rootstock would be the most suitable for pear in order to tolerate a salt stress condition. It has been reported that pear and quince have different ability in the uptake, translocation and accumulation of chloride (Cl-) and sodium (Na+) ions, when plants were irrigated for one season with saline water (5 dS/m). The aim of the present work was to deepen these aspects and investigate salt stress responses in pear and quince. Two different experiments have been performed: a “short-term” trial in a growth chamber and a “long-term” experiment in the open field. In the short-term experiment, three different genotypes usually adopted as pear rootstocks (MC, BA29 and Farold®40) and the pear variety Abbé Fétel own rooted have been compared under salt stress conditions. The trial was performed in a hydroponic culture system, applying a 90 mM NaCl stress to half of the plants, after five weeks of normal growth in Hoagland’s solution. During the three-weeks of salt stress treatment, physiological, mineral and molecular analyses were performed in order to monitor, for each genotype, the development of the salt stress responses in comparison with the corresponding “unstressed” plants. Farold®40 and Abbé Fétel own rooted showed the onset of leaf necrosis, due to salt toxicity, one week before quinces. Moreover, quinces displayed a significant delay in premature senescence of old leaves, while pears emerged for their ability to regenerate new leaves from apparently dead foliage with the salt stress still running. Physiological measurements, such as shoots length, chlorophyll (Chl) content, and photosynthesis, have been carried out and revealed that pears exhibited a significant reduction in water content and a wilting aspect, while for quinces a decrease in Chl content and a growth slowdown were observed. At the end of the trial, all plants were collected and organs separated for dry weight estimation and mineral analyses (Cu, Fe, Mn, Zn Mg, Ca, K, Na and Cl). Mineral contents have been affected by salinity; same macro/micro nutrients were altered in some organs or relocated within the plant. This plant response could have partially contributed to face the salt stress. Leaves and roots have been harvested for molecular analyses at four different times during stress conditions. Molecular analyses consisted of the gene expression study of three main ion transporters, well known in Arabidopsis thaliana as salt-tolerance determinants in the “SOS” pathway: NHX1 (tonoplast Na+/H+ antiporter), SOS1 (plasmalemma Na+/H+ antiporter) and HKT1 (K+ high-affinity and Na+ low-affinity transporter). These studies showed that two quince rootstocks adopted different responsive mechanisms to NaCl stress. BA29 increased its Na+ sequestration activity into leaf vacuoles, while MC enhanced temporarily the same ability, but in roots. Farold®40, instead, exhibited increases in SOS1 and HKT1 expression mainly at leaf level in the attempt to retrieve Na+ from xylem, while Abbé Fétel differently altered the expression of these genes in roots. Finally, each genotype showed a peculiar response to salt stress that was the sum of its ability in Na+ exclusion, osmotic tolerance and tissue tolerance. In the long-term experiment, potted trees of the pear variety Abbé Fétel grafted on different rootstocks (MC, BA29 and Farold®40), or own rooted and also rootstocks only were subjected to a salt stress through saline water irrigation with an electrical conductivity of 5 dS/m for two years. The purposes of this study were to evaluate salinity effects on physiological (shoot length, number of buds, photosynthesis, etc.) and yield parameters of cultivar Abbé Fétel in the different combinations and to determine the salt amount that pear is able to tolerate over the years. With this work, we confirmed the previous hypothesis that pear, despite being classified as a salt-sensitive fruit tree, can be cultivated for two years under saline water irrigation, without showing any salt toxicity symptoms or severe drawbacks on plant development and production. Among different combinations, Abbé Fétel grafted on MC resulted interesting for its peculiar behaviors under salt stress conditions. In the near future, further investigations on physiological and molecular aspects will be necessary to enrich and broaden the knowledge of salt stress responses in pear.

Bonded structures for enhanced damage tolerant pressurized fuselages

Adhesive bonding provides solutions to realize cost effective and low weight aircraft fuselage structures, in particular where the Damage Tolerance (DT) is the design criterion. Bonded structures that combine Metal Laminates (MLs) and eventually Selective Reinforcements can guarantee slow crack propagation, crack arrest and large damage capability. To optimize the design exploiting the benefit of bonded structures incorporating selective reinforcement requires reliable analysis tools. The effect of bonded doublers / selective reinforcements is very difficult to be predicted numerically or analytically due to the complexity of the underlying mechanisms and failures modes acting. Reliable predictions of crack growth and residual strength can only be based on sound empirical and phenomenological considerations strictly related to the specific structural concept. Large flat stiffened panels that combine MLs and selective reinforcements have been tested with the purpose of investigating solutions applicable to pressurized fuselages. The large test campaign (for a total of 35 stiffened panels) has quantitatively investigated the role of the different metallic skin concepts (monolithic vs. MLs) of the aluminum, titanium and glass-fiber reinforcements, of the stringers material and cross sections and of the geometry and location of doublers / selective reinforcements. Bonded doublers and selective reinforcements confirmed to be outstanding tools to improve the DT properties of structural elements with a minor weight increase. However the choice of proper materials for the skin and the stringers must be not underestimated since they play an important role as well. A fuselage structural concept has been developed to exploit the benefit of a metal laminate design concept in terms of high Fatigue and Damage Tolerance (F&DT) performances. The structure used laminated skin (0.8mm thick), bonded stringers, two different splicing solutions and selective reinforcements (glass prepreg embedded in the laminate) under the circumferential frames. To validate the design concept a curved panel was manufactured and tested under loading conditions representative of a single aisle fuselage: cyclic internal pressurization plus longitudinal loads. The geometry of the panel, design and loading conditions were tailored for the requirements of the upper front fuselage. The curved panel has been fatigue tested for 60 000 cycles before the introduction of artificial damages (cracks in longitudinal and circumferential directions). The crack growth of the artificial damages has been investigated for about 85 000 cycles. At the end a residual strength test has been performed with a “2 bay over broken frame” longitudinal crack. The reparability of this innovative concept has been taken into account during design and demonstrated with the use of an external riveted repair. The F&DT curved panel test has confirmed that a long fatigue life and high damage tolerance can be achieved with a hybrid metal laminate low weight configuration. The superior fatigue life from metal laminates and the high damage tolerance characteristics provided by integrated selective reinforcements are the key concepts that provided the excellent performances. The weight comparison between the innovative bonded concept and a conventional monolithic riveted design solution showed a significant potential weight saving but the weight advantages shall be traded off with the additional costs.

Reliable and Variation-Tolerant Interconnection Network for Low Power MPSOCS

Multi-Processor SoC (MPSOC) design brings to the foreground a large number of challenges, one of the most prominent of which is the design of the chip interconnection. With a number of on-chip blocks presently ranging in the tens, and quickly approaching the hundreds, the novel issue of how to best provide on-chip communication resources is clearly felt. Scaling down of process technologies has increased process and dynamic variations as well as transistor wearout. Because of this, delay variations increase and impact the performance of the MPSoCs. The interconnect architecture inMPSoCs becomes a single point of failure as it connects all other components of the system together. A faulty processing element may be shut down entirely, but the interconnect architecture must be able to tolerate partial failure and variations and operate with performance, power or latency overhead. This dissertation focuses on techniques at different levels of abstraction to face with the reliability and variability issues in on-chip interconnection networks. By showing the test results of a GALS NoC testchip this dissertation motivates the need for techniques to detect and work around manufacturing faults and process variations in MPSoCs’ interconnection infrastructure. As a physical design technique, we propose the bundle routing framework as an effective way to route the Network on Chips’ global links. For architecture-level design, two cases are addressed: (I) Intra-cluster communication where we propose a low-latency interconnect with variability robustness (ii) Inter-cluster communication where an online functional testing with a reliable NoC configuration are proposed. We also propose dualVdd as an orthogonal way of compensating variability at the post-fabrication stage. This is an alternative strategy with respect to the design techniques, since it enforces the compensation at post silicon stage.

Variability-tolerant High-reliability Multicore Platforms

Next generation electronic devices have to guarantee high performance while being less power-consuming and highly reliable for several application domains ranging from the entertainment to the business. In this context, multicore platforms have proven the most efficient design choice but new challenges have to be faced. The ever-increasing miniaturization of the components produces unexpected variations on technological parameters and wear-out characterized by soft and hard errors. Even though hardware techniques, which lend themselves to be applied at design time, have been studied with the objective to mitigate these effects, they are not sufficient; thus software adaptive techniques are necessary. In this thesis we focus on multicore task allocation strategies to minimize the energy consumption while meeting performance constraints. We firstly devise a technique based on an Integer Linear Problem formulation which provides the optimal solution but cannot be applied on-line since the algorithm it needs is time-demanding; then we propose a sub-optimal technique based on two steps which can be applied on-line. We demonstrate the effectiveness of the latter solution through an exhaustive comparison against the optimal solution, state-of-the-art policies, and variability-agnostic task allocations by running multimedia applications on the virtual prototype of a next generation industrial multicore platform. We also face the problem of the performance and lifetime degradation. We firstly focus on embedded multicore platforms and propose an idleness distribution policy that increases core expected lifetimes by duty cycling their activity; then, we investigate the use of micro thermoelectrical coolers in general-purpose multicore processors to control the temperature of the cores at runtime with the objective of meeting lifetime constraints without performance loss.

Effects of Resources Exploitation on Water Quality: case studies in Salt Water Intrusion and Acid Mine Drainage

Throughout the world, pressures on water resources are increasing, mainly as a result of human activity. Because of their accessibility, groundwater and surface water are the most used reservoirs. The evaluation of the water quality requires the identification of the interconnections among the water reservoirs, natural landscape features, human activities and aquatic health. This study focuses on the estimation of the water pollution linked to two different environmental issues: salt water intrusion and acid mine drainage related to the exploitation of natural resources. Effects of salt water intrusion occurring in the shallow aquifer north of Ravenna (Italy) was analysed through the study of ion- exchange occurring in the area and its variance throughout the year, applying a depth-specific sampling method. In the study area were identified ion exchange, calcite and dolomite precipitation, and gypsum dissolution and sulphate reduction as the main processes controlling the groundwater composition. High concentrations of arsenic detected only at specific depth indicate its connexion with the organic matter. Acid mine drainage effects related to the tin extraction in the Bolivian Altiplano was studied, on water and sediment matrix. Water contamination results strictly dependent on the seasonal variation, on pH and redox conditions. During the dry season the strong evaporation and scarce water flow lead to low pH values, high concentrations of heavy metals in surface waters and precipitation of secondary minerals along the river, which could be released in oxidizing conditions as demonstrated through the sequential extraction analysis. The increase of the water flow during the wet season lead to an increase of pH values and a decrease in heavy metal concentrations, due to dilution effect and, as e.g. for the iron, to precipitation.

Fault detection, diagnosis and active fault tolerant control for a satellite attitude control system

Modern control systems are becoming more and more complex and control algorithms more and more sophisticated. Consequently, Fault Detection and Diagnosis (FDD) and Fault Tolerant Control (FTC) have gained central importance over the past decades, due to the increasing requirements of availability, cost efficiency, reliability and operating safety. This thesis deals with the FDD and FTC problems in a spacecraft Attitude Determination and Control System (ADCS). Firstly, the detailed nonlinear models of the spacecraft attitude dynamics and kinematics are described, along with the dynamic models of the actuators and main external disturbance sources. The considered ADCS is composed of an array of four redundant reaction wheels. A set of sensors provides satellite angular velocity, attitude and flywheel spin rate information. Then, general overviews of the Fault Detection and Isolation (FDI), Fault Estimation (FE) and Fault Tolerant Control (FTC) problems are presented, and the design and implementation of a novel diagnosis system is described. The system consists of a FDI module composed of properly organized model-based residual filters, exploiting the available input and output information for the detection and localization of an occurred fault. A proper fault mapping procedure and the nonlinear geometric approach are exploited to design residual filters explicitly decoupled from the external aerodynamic disturbance and sensitive to specific sets of faults. The subsequent use of suitable adaptive FE algorithms, based on the exploitation of radial basis function neural networks, allows to obtain accurate fault estimations. Finally, this estimation is actively exploited in a FTC scheme to achieve a suitable fault accommodation and guarantee the desired control performances. A standard sliding mode controller is implemented for attitude stabilization and control. Several simulation results are given to highlight the performances of the overall designed system in case of different types of faults affecting the ADCS actuators and sensors.