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).

Analysis of cumulative effects of multiple stressors on saltmarshes and consideration of management options

Natural systems face pressures exerted by natural physical-chemical forcings and a myriad of co-occurring human stressors that may interact to cause larger than expected effects, thereby presenting a challenge to ecosystem management. This thesis aimed to develop new information that can contribute to reduce the existing knowledge gaps hampering the holistic management of multiple stressors. I undertook a review of the state-of-the-art methods to detect, quantify and predict stressor interactions, identifying techniques that could be applied in this thesis research. Then, I conducted a systematic review of saltmarsh multiple stressor studies in conjunction with a multiple stressor mapping exercise for the study system in order to infer potential important synergistic stressor interactions. This analysis identified key stressors that are affecting the study system, but also pointed to data gaps in terms of driver and pressure data and raised issues for potentially overlooked stressors. Using field mesocosms, I explored how a local stressor (nutrient availability) affects the responses of saltmarsh vegetation to a global stressor (increased inundation) in different soil types. Results indicate that saltmarsh vegetation would be more drastically affected by increased inundation in low than in medium organic matter soils, and especially in estuaries already under high nutrient availability. In another field experiment, I examined the challenges of managing co-occurring and potentially interacting local stressors on saltmarsh vegetation: recreational trampling and smothering by deposition of excess macroalgal wrack due to high nutrient loads. Trampling and wrack prevention had interacting effects, causing non-linear responses of the vegetation to simulated management of these stressors, such that vegetation recovered only in those treatments simulating the combined prevention of both stressors. During this research I detected, using molecular genetic methods, a widespread presence of S. anglica (and to a lesser extent S. townsendii), two previously unrecorded non-native Spartinas in the study areas.

Psychological Sense of Community: A New Construct for the Field of Management

This article introduces a new construct to the field of management called Psychological Sense of Community (PSOC). This is important because management scholars are calling for the creation of communities in organizations in an environment that lacks appropriate construct development. The aims of this article are threefold: (a) develop a working definition of PSOC via a review of the extant literature on PSOC from other disciplines with the goal of translating it into the domain of management, (b) synthesize findings from parallel literatures on the outcomes of PSOC with an eye toward exploring the relevance of such outcomes in management contexts, and (c) assess the value of PSOC as it relates to its uniqueness in relation to other prominent management constructs and its scope of applicability in a variety of management inquiry areas.

Effects of management on native and exotic plant communities in Pictured Rocks National Lakeshore in the Upper Peninsula of Michigan

Ecological disturbances may be caused by a range of biotic and abiotic factors. Among these are disturbances that result from human activities such as the introduction of exotic plants and land management activities. This dissertation addresses both of these types of disturbance in ecosystems in the Upper Peninsula of Michigan. Invasive plants are a significant cause of disturbance at Pictured Rocks Natural Lakeshore. Management of invasive plants is dependent on understanding what areas are at risk of being invaded, what the consequences of an invasion are on native plant communities and how effective different tools are for managing the invasive species. A series of risk models are described that predict three stages of invasion (introduction, establishment and spread) for eight invasive plant species at Pictured Rocks National Lakeshore. These models are specific to this location and include species for which models have not previously been produced. The models were tested by collecting point data throughout the park to demonstrate their effectiveness for future detection of invasive plants in the park. Work to describe the impacts and management of invasive plants focused on spotted knapweed in the sensitive Grand Sable Dunes area of Pictured Rocks National Lakeshore. Impacts of spotted knapweed were assessed by comparing vegetation communities in areas with varying amounts of spotted knapweed. This work showed significant increases in species diversity in areas invaded by knapweed, apparently as a result of the presence of a number of non-dune species that have become established in spotted knapweed invaded areas. An experiment was carried out to compare annual spot application of two herbicides, Milestone® and Transline® to target spotted knapweed. This included an assessment of impacts of this type of treatment on non-target species. There was no difference in the effectiveness of the two herbicides, and both significantly reduced the density of spotted knapweed during the course of the study. Areas treated with herbicide developed a higher percent cover of grasses during the study, and suffered limited negative impacts on some sensitive dune species such as beach pea and dune stitchwort, and on some other non-dune species such as hawkweed. The use of these herbicides to reduce the density of spotted knapweed appears to be feasible over large scales.

Taking action against ocean acidification: A review of management and policy options

Ocean acidification has emerged over the last two decades as one of the largest threats to marine organisms and ecosystems. However, most research efforts on ocean acidification have so far neglected management and related policy issues to focus instead on understanding its ecological and biogeochemical implications. This shortfall is addressed here with a systematic, international and critical review of management and policy options. In particular, we investigate the assumption that fighting acidification is mainly, but not only, about reducing CO2 emissions, and explore the leeway that this emerging problem may open in old environmental issues. We review nine types of management responses, initially grouped under four categories: preventing ocean acidification; strengthening ecosystem resilience; adapting human activities; and repairing damages. Connecting and comparing options leads to classifying them, in a qualitative way, according to their potential and feasibility. While reducing CO2 emissions is confirmed as the key action that must be taken against acidification, some of the other options appear to have the potential to buy time, e.g. by relieving the pressure of other stressors, and help marine life face unavoidable acidification. Although the existing legal basis to take action shows few gaps, policy challenges are significant: tackling them will mean succeeding in various areas of environmental management where we failed to a large extent so far.