Ecophysiology (from Greek οἶκος, oikos, "house(hold)"; φύσις, physis, "nature, origin"; and -λογία, -logia) or environmental physiology is a biological discipline which studies the adaptation of organism's physiology to environmental conditions. It is closely related to comparative physiology and evolutionary physiology.
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Plant ecophysiology is an experimental science that seeks to describe the physiological mechanisms underlying ecological observations. In other words, ecophysiologists, address ecological questions about the controls over the growth, reproduction, survival, abundance, and geographical distribution of plants, as these processes are affected by interactions between plants with their physical, chemical, and biotic environment. These ecophysiological patterns and mechanisms can help us understand the functional significance of specific plant traits and their evolutionary heritage. The questions addressed by ecophysiologists are derived from a higher level of integration, i.e. from “ecology” in its broadest sense, including questions originating from agriculture, horticulture, forestry, and environmental sciences. However, ecophysiological explanations often require mechanistic understanding at a lower level of integration (physiology, biochemistry, biophysics, molecular biology). It is therefore essential for an ecophysiologist to appreciate both ecological questions and biophysical, biochemical, and molecular methods and processes. A modern ecophysiologist thus requires a good understanding of both the molecular aspects of plant processes and the functioning of the intact plant in its environmental context.
In addition, many societal issues, often pertaining to agriculture, environmental change or nature conservation, benefit from an ecophysiological perspective. Ecophysiologists may investigate the effects of environmental stresses, e.g. extremes of temperature, light and water availability, on the ability of a plant to metabolise normally. For instance, the physiological impacts can be investigated by measuring chlorophyll fluorescence.
In many cases, animals are able to escape unfavourable and changing environmental factors such as heat, cold, drought or floods, while plants are unable to move away and therefore must endure the adverse conditions or perish (animals go places, plants grow places). Plants are therefore phenotypically plastic and have an impressive array of genes which aid in adapting to changing conditions. It is hypothesized that this large number of genes can be partly explained by plant species' need to adapt to a wider range of conditions.
In response to extremes of temperature plants can produce various proteins that protect them from the damaging effects of ice formation and falling rates of enzyme catalysis at low temperatures and enzyme denaturation and increased photorespiration at high temperatures. As temperatures fall production of antifreeze proteins and dehydrins rise. As temperatures rise production of heat shock proteins rise. Plants can also adapt their morphology (change their shape) to adapt to longer term temperature changes. For example to protect against frost cell walls can be made thicker and stronger (through more lignification) so that water freezes in between cells (in the apoplast) and not in the cells (in the cytoplasm). Cell membranes are also affected by changes in temperature and can cause the membrane to lose its fluid properties and become a gel in cold conditions or become leaky in hot conditions. This can affect the movement of compounds across the membrane. To prevent these changes plants can change the composition of their membranes. In cold conditions more unsaturated fatty acids are placed in the membrane and in hot conditions more saturated fatty acids are inserted. Plants adapted to extreme dry and arid climates are known as xerophytic.
Strong winds can affect plants by uprooting them or damaging their leaves. Whereas responses to temperature changes are often acclimatory there is not enough time for this to occur to wind and so plants must be permanently adapted to survive potentially damaging winds. Examples of adaptations to prevent damage include having leaves with thick cuticles, and large root systems. One reason that deciduous trees shed their leaves in the autumn is to reduce their surface area and make it less likely that they will be blown over.
Too much or too little water can damage plants. If there is too little water then tissues will dehydrate and the plant may die. If the soil becomes waterlogged then the soil will become anoxic (low in oxygen) which could kill the roots. If tissues become dehydrated they lose turgor which in turn causes abscisic acid, a plant hormone, to be produced. This travels throughout the plant and has a number of effects. It increases the number of closed stomata, reducing water loss and also stimulates growth of the roots in an attempt to increase the supply of water. Some plants, for example maize and rice are able to produce aerenchyma in their roots if the soil they are growing in becomes waterlogged. These are hollow vessels that allow the diffusion on oxygen into the roots.
The concentration of CO2 in the atmosphere is rising due to deforestation and the combustion of fossil fuels. Plants use CO2 as a substrate in photosynthesis and it was previously thought that as the concentration of CO2 rises that the efficiency of photosyntheis would increase leading to increased growth. Studies using Free-air concentration enrichment have however shown that crop yields are only increased by up to 8%.[1] Studies of specimens in herbariums have shown that the number of stomata on leaves has decreased over the last 150 years as the concentration of CO2 has risen.[2] Stomata let CO2 diffuse into the leaf but let water leave at the same time. Plants are acclimating to increased CO2 concentrations by having fewer stomata because they allow the same amount of CO2 into the leaf as before yet they use less water.[3] It has also been found that the nitrogen level falls when plants are grown at elevated CO2 due to plants needing less rubisco to fix the same amount of CO2. The levels of other micronutrients also fall which may have consequences for human nutrition in the future.[4]
The environment can have major influences on human physiology. Environmental effects on human physiology are numerous; one of the most carefully studied effects is the alterations in thermoregulation in the body due to outside stresses. This is necessary because in order for enzymes to function, blood to flow, and for various body organs to operate, temperature must remain at consistent, balanced levels.
To achieve this, the body alters three main things to achieve a constant, normal body temperature:
The hypothalamus plays an important role in thermoregulation. It connects to thermal receptors in the dermis, and detects changes in surrounding blood to make decisions of whether to stimulate internal heat production, or to stimulate evaporation.
There are two main types of stresses that can be experienced due to extreme, environmental temperatures; heat stress and cold stress.
Heat stress is physiologically combated in four ways: radiation, conduction, convection, and evaporation. Cold stress is physiologically combated by shivering, accumulation of body fat, circulatory adaptations (that provide an efficient transfer of heat to the epidermis), and increased blood flow to the extremities.
There is one part of the body fully equipped to deal with cold stress. The respiratory system protects itself against damage by warming the incoming air to 80-90 degrees Fahrenheit before it reaches the bronchi. This means that not even the most frigid of temperatures can damage the respiratory tract.
In both types of temperature related stress, it is important to remain well hydrated. Hydration reduces cardiovascular strain, enhances the ability of energy processes to occur, and reduces feelings of exhaustion.
Extreme temperatures are not the only obstacles that humans face. High altitudes also pose serious physiological challenges on the body. Some of these effects are reduced arterial P02, the rebalancing of the acid-base content in body fluids, increased hemoglobin, increased RBC synthesis, enhanced circulation, and increased levels of the glycolysis byproduct 2,3 diphosphoglycerate which promotes off-loading of O2 by hemoglobin in the hypoxic tissues.
Environmental factors can play a huge role in the human body's fight for homeostasis. Fortunately, humans have found ways to adapt, both physiologically and tangibly.
George A. Bartholomew (1919–2006) was a founder of animal physiological ecology. He served on the faculty at UCLA from 1947 to 1989, and almost 1,200 individuals can trace their academic lineages to him.[5] Knut Schmidt-Nielsen (1915–2007) was also an important contributor to this specific scientific field as well as comparative physiology.
Hermann Rahn (1912–1990) was a early leader in the field of environmental physiology. Starting out in the field of zoology with a PhD from University of Rochester (1933), Rahn began teaching physiology at the University of Rochester in 1941. It was there that he partnered with Wallace O. Fenn to publish A Graphical Analysis of the Respiratory Gas Exchange in 1955. This paper included the landmark O2-CO2 diagram, which formed basis for much of Rahn's future work. Rahn's research into applications of this diagram lead to the development of aerospace medicine and advancements in hyperbaric breathing and high-altitude respiration. Rahn later joined the University at Buffalo in 1956 as the Lawrence D. Bell Professor and Chairman of the Department of Physiology. As Chairman, Rahn surrounded himself with outstanding faculty and made the University an international research center in environmental physiology.