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Ecological Effects of Environmental Stressors  

Bill Freedman

Regimes of environmental stress are exceedingly complex. Particular stressors exist within continua of intensity of environmental factors. Those factors interact with each other, and their detrimental effects on organisms are manifest only at relatively high or low strengths of exposure—in fact, many of them are beneficial at intermediate levels of intensity. Although a diversity of environmental factors is manifest at any time and place, only one or a few of them tend to be dominant as stressors. It is useful to distinguish between stressors that occur as severe events (disturbances) and those that are chronic in their exposure, and to aggregate the kinds of stressors into categories (while noting some degree of overlap among them). Climatic stressors are associated with extremes of temperature, solar radiation, wind, moisture, and combinations of these factors. They act as stressors if their condition is either insufficient or excessive, in comparison with the needs and comfort zones of organisms or ecosystem processes. Chemical stressors involve environments in which the availability of certain substances is too low to satisfy biological needs, or high enough to cause toxicity or another physiological detriment to organisms or to higher-level attributes of ecosystems. Wildfire is a disturbance that involves the combustion of much of the biomass of an ecosystem, affecting organisms by heat, physical damage, and toxic substances. Physical stress is a disturbance in which an exposure to kinetic energy is intense enough to damage organisms and ecosystems (such as a volcanic blast, seismic sea wave, ice scouring, or anthropogenic explosion or trampling). Biological stressors are associated with interactions occurring among organisms. They may be directly caused by such trophic interactions as herbivory, predation, and parasitism. They may also indirectly affect the intensity of physical or chemical stressors, as when competition affects the availability of nutrients, moisture, or space. Extreme environments are characterized by severe regimes of stressors, which result in relatively impoverished ecosystem development. This may be a consequence of either natural or anthropogenic stressors. If a regime of environmental stress intensifies, the resulting responses include a degradation of the structure and function of affected ecosystems and of ecological integrity more generally. In contrast, a relaxation of environmental stress allows some degree of ecosystem recovery.


Tomatoes: A Model Crop of Solanaceous Plants  

Raheel Anwar, Tahira Fatima, and Autar K. Mattoo

The modern-day cultivated and highly consumed tomato has come a long way from its ancestor(s), which were in the wild and not palatable. Breeding strategies made the difference in making desirable food, including tomato, available for human consumption. However, like other horticultural produce, the shelf life of tomato is short, which results in losses that can reach almost 50% of the produce, more so in developing countries than in countries with advanced technologies and better infrastructure. Food security concerns are real, especially taking into consideration that the population explosion anticipated by 2050 will require more food production and the production of more nutritious food, which applies as much to the tomato crop as the other crops. Today’s consumer has become aware and is looking for nutritious foods for a healthful and long life. Little was done until recently to generate nutritionally enhanced produce including fruits/vegetables. Also, extreme environments add to plant stress and impact yield and nutritional quality of produce. Recent developments in understandings of the plant/fruit genetics and progress made in developing genetic engineering technologies, including the use of CRISPR-Cas9, raise hopes that a better tomato with a high dose of nutrition and longer-lasting quality will become a reality.


Citrus History, Taxonomy, Breeding, and Fruit Quality  

Paolo Inglese and Giuseppe Sortino

In May, every year since 1857, in the great park of Sans-Souci in Potsdam just outside Berlin—a park begun in 1745 by Emperor Frederick II of Hohenzollern and expanded a century later by Frederick William IV—the doors of the great Orangerie open in and a Renaissance-style garden called Sizilianischer Garten is set up. On horse-drawn carriages, large olive and citrus trees are brought outdoors, and are then raised in masters. For the young European who, in the second half of the 18th century and in the first decades of the following, traveled to Italy to see and study Renaissance culture and the remains of Greek civilization, the citrus species and fruits and groves of southern Italy became the ultimate symbol of beauty and a sort of status symbol of wealth, particularly that of landowners. Nothing is more expressive of the fascination of their fruit than Abu-l-Hasan Ali’s 12th-century writings: “Come on, enjoy your harvested orange: happiness is present when it is present. / Welcome the cheeks of the branches, and welcome the stars of the trees! / It seems that the sky has lavished gold and that the earth has formed some shiny spheres.” Indeed, Citrus spp. are among the most important crops and consumed fruit worldwide. Their co-evolution due to a millennial agricultural utilization resulted in a complexity of species and cultivated varieties derived by natural or induced mutations, crossing and breeding the “original” species (Citrus medica, Citrus maxima, Citrus reticulate, Fortunella japonica) and their main progenies (C. aurantium, C. sinensis, Citrus limon, Citrus paradisi, Citrus clementina, etc.). Citrus spread from the original tropical and subtropical regions of southeast Asia toward the Mediterranean countries of Europe and North Africa and, after 1492, in the Americas, not to mention South Africa and Australia, where they still have a very important role. Citrus species, wherever they have been cultivated, quickly became the protagonists of the letters and the arts, as well as the markets and gastronomy, and can even be found in religious ceremonies, such as for Feast of Tabernacles (Sukkot). Studies on Citrus botany, cultivation, and utilization have been pursued since the early stages of the fruit’s domestication and grew following their introduction in Europe, the Americas, Africa, and Australia. Citrus research involves many different aspects: such as the study of citrus origin and botanical classification; citrus growing, propagation, and orchard management; citrus fruit quality, utilization and industry; citrus gardening and ornamentals; citrus in arts and manufacturing.


Natural Environments, Health, and Well-Being  

Matilda van den Bosch

Human beings are part of natural ecosystems and depend on them for their survival. In a rapidly changing environment and with increasing urbanization, this dependence is challenged. Natural environments affect human health and well-being both directly and indirectly. Urban green and blue areas provide opportunities for stress recovery and physical activity. They offer spaces for social interactions in the neighborhood and places for children’s play. Chronic stress, physical inactivity, and lack of social cohesion are three major risk factors for noncommunicable diseases, and therefore abundant urban greenery is an important asset for health promotion. Through numerous ecosystem services natural environments play a fundamental role in protecting health. Various populations depend on nature for basic material, such as fresh water, wood, fuel, and nutritious food. Biodiverse natural areas are also necessary for regulating the environment and for mitigating and adapting to climate change. For example, tree canopy cover can reduce the urban heat island effect substantially, preventing excess morbidity during heat waves. This natural heat-reducing effect also lessens the need for air conditioning systems and as a consequence decreases energy spending. Urban trees also support storm-water management, preventing flooding and related health issues. Air pollution is a major threat to population health. Urban trees sequester pollutants and, even though the effect may be relatively small, given the severity of the problem it may still have some public-health implications. The evidence around the effects of natural environments on health and well-being is steadily increasing. Several pathways and mechanisms are suggested, such as health services through functional ecosystems, early life exposure to biodiverse microbiota, which is important for the immune-system development, and sensory exposure, which has direct neurobiological impact supporting cognitive development and stress resilience. Support for several pathways is at hand that shows lower mortality rates and prevalence of cardiovascular and respiratory diseases, healthier pregnancy outcomes, reduced health inequalities, and improved mental health in urban areas with greater amounts of green and blue space. Altogether, the interactions between healthy natural environments and healthy people are multiple and complex, and require interdisciplinary attention and action for full understanding and resilient development of both nature and human beings.


Cities, Green Space, and Mental Well-Being  

Jenny Roe

Mental and behavioral disorders account for approximately 7.4% of the global burden of disease, with depression now the world’s leading cause of disability. One in four people in the world will suffer from a mental health problem at some point in their life. City planning and design holds much promise for reducing this burden of disease, and for offering solutions that are affordable, accessible and equitable. Increasingly urban green space is recognized as an important social determinant of health, with the potential to protect mental health – for example, by buffering against life stressors - as well as relieving the symptom severity of specific psychiatric disorders. Pathways linking urban green space with mental wellbeing include the ability of natural stimuli – trees, water, light patterns – to promote ‘involuntary attention’ allowing the brain to disengage and recover from cognitive fatigue. This article brings together evidence of the positive effects of urban green space on common mental health problems (i.e. stress, anxiety, depression) together with evidence of its role in the symptom relief of specific psychiatric disorders, including schizophrenia and psychosis, post-traumatic stress disorder (PTSD), dementia, attention deficit/hyperactivity Disorder (ADHD) and autism. Urban green space is a potential force for building mental health: city planners, urban designers, policy makers and public health professionals need to maximize the opportunities in applying green space strategies for both health prevention and in supporting treatment of mental ill health.


Water Security  

Claudia Sadoff, David Grey, and Edoardo Borgomeo

Water security has emerged in the 21st century as a powerful construct to frame the water objectives and goals of human society and to support and guide local to global water policy and management. Water security can be described as the fundamental societal goal of water policy and management. This article reviews the concept of water security, explaining the differences between water security and other approaches used to conceptualize the water-related challenges facing society and ecosystems and describing some of the actions needed to achieve water security. Achieving water security requires addressing two fundamental challenges at all scales: enhancing water’s productive contributions to human and ecosystems’ well-being, livelihoods and development, and minimizing water’s destructive impacts on societies, economies, and ecosystems resulting, for example, from too much (flood), too little (drought) or poor quality (polluted) water.


Mining, Ecological Engineering, and Metals Extraction for the 21st Century  

Margarete Kalin, William N. Wheeler, Michael P. Sudbury, and Bryn Harris

The first treatise on mining and extractive metallurgy, published by Georgius Agricola in 1556, was also the first to highlight the destructive environmental side effects of mining and metals extraction, namely dead fish and poisoned water. These effects, unfortunately, are still with us. Since 1556, mining methods, knowledge of metal extraction, and chemical and microbial processes leading to the environmental deterioration have grown tremendously. Man’s insatiable appetite for metals and energy has resulted in mines vastly larger than those envisioned in 1556, compounding the deterioration. The annual amount of mined ore and waste rock is estimated to be 20 billion tons, covering 1,000 km2. The industry also annually consumes 80 km3 of freshwater, which becomes contaminated. Since metals are essential in modern society, cost-effective, sustainable remediation measures need to be developed. Engineered covers and dams enclose wastes and slow the weathering process, but, with time, become permeable. Neutralization of acid mine drainage produces metal-laden sludges that, in time, release the metals again. These measures are stopgaps at best, and are not sustainable. Focus should be on inhibiting or reducing the weathering rate, recycling, and curtailing water usage. The extraction of only the principal economic mineral or metal generally drives the economics, with scant attention being paid to other potential commodities contained in the deposit. Technology exists for recovering more valuable products and enhancing the project economics, resulting in a reduction of wastes and water consumption of up to 80% compared to “conventional processing.” Implementation of such improvements requires a drastic change, a paradigm shift, in the way that the industry approaches metals extraction. Combining new extraction approaches, more efficient water usage, and ecological engineering methods to deal with wastes will increase the sustainability of the industry and reduce the pressure on water and land resources. From an ecological perspective, waste rock and tailings need to be thought of as primitive ecosystems. These habitats are populated by heat-, acid- and saline-loving microbes (extremophiles). Ecological engineering utilizes geomicrobiological, physical, and chemical processes to change the mineral surface to encourage biofilm growth (the microbial growth form) within wastes by enhancing the growth of oxygen-consuming microbes. This reduces oxygen available for oxidation, leading to improved drainage quality. At the water–sediment interface, microbes assist in the neutralization of acid water (Acid Reduction Using Microbiology). To remove metals from the waste water column, indigenous biota are promoted (Biological Polishing) with inorganic particulate matter as flocculation agents. This ecological approach generates organic matter, which upon death settles with the adsorbed metals to the sediment. Once the metals reach the deeper, reducing zones of the sediments, microbial biomineralization processes convert the metals to relatively stable secondary minerals, forming biogenic ores for future generations. The mining industry has developed and thrived in an age when resources, space, and water appeared limitless. With the widely accepted rise of the Anthropocene global land and water shortages, the mining industry must become more sustainable. Not only is a paradigm shift in thinking needed, but also the will to implement such a shift is required for the future of the industry.