Ecophysiology

Ecophysiology (from

Plants

Plant ecophysiology is concerned largely with two topics: mechanisms (how plants sense and respond to environmental change) and scaling or integration (how the responses to highly variable conditions—for example, gradients from full sunlight to 95% shade within tree canopies—are coordinated with one another), and how their collective effect on plant growth and gas exchange can be understood on this basis.^{[citation needed]}

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 that aid in acclimating to changing conditions. It is hypothesized that this large number of genes can be partly explained by plant species' need to live in a wider range of conditions.

Light

]

As with most abiotic factors, light intensity (irradiance) can be both suboptimal and excessive. Suboptimal light (shade) typically occurs at the base of a plant canopy or in an understory environment.

Shade tolerant

plants have a range of adaptations to help them survive the altered quantity and quality of light typical of shade environments.

Excess light occurs at the top of canopies and on open ground when cloud cover is low and the sun's zenith angle is low, typically this occurs in the tropics and at high altitudes. Excess light incident on a leaf can result in

]

Light intensity is also an important component in determining the temperature of plant organs (energy budget).^[citation needed]

Temperature

In response to extremes of temperature, plants can produce various

are inserted.

Plants can avoid overheating by minimising the amount of sunlight absorbed and by enhancing the cooling effects of wind and transpiration. Plants can reduce light absorption using reflective leaf hairs, scales, and waxes. These features are so common in warm dry regions that these habitats can be seen to form a 'silvery landscape' as the light scatters off the canopies.^[2] Some species, such as Macroptilium purpureum, can move their leaves throughout the day so that they are always orientated to avoid the sun (paraheliotropism).^[3] Knowledge of these mechanisms has been key to breeding for heat stress tolerance in agricultural plants.^{[citation needed]}

Plants can avoid the full impact of low temperature by altering their microclimate. For example, Raoulia plants found in the uplands of New Zealand are said to resemble 'vegetable sheep' as they form tight cushion-like clumps to insulate the most vulnerable plant parts and shield them from cooling winds. The same principle has been applied in agriculture by using plastic mulch to insulate the growing points of crops in cool climates in order to boost plant growth.^[4]

Water

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 can kill the roots of the plant.^{[citation needed]}

The ability of plants to access water depends on the structure of their roots and on the

In very dry soil, plants close their stomata to reduce transpiration and prevent water loss. The closing of the stomata is often mediated by chemical signals from the root (i.e.,

If drought continues, the plant tissues will dehydrate, resulting in a loss of

) have a range of more specialized mechanisms to maintain water and/or protect tissues when desiccation occurs.

Waterlogging reduces the supply of oxygen to the roots and can kill a plant within days. Plants cannot avoid waterlogging, but many species overcome the lack of oxygen in the soil by transporting oxygen to the root from tissues that are not submerged. Species that are tolerant of waterlogging develop specialised roots near the soil surface and aerenchyma to allow the diffusion of oxygen from the shoot to the root. Roots that are not killed outright may also switch to less oxygen-hungry forms of cellular respiration.^[7] Species that are frequently submerged have evolved more elaborate mechanisms that maintain root oxygen levels, such as the aerial roots seen in mangrove forests.^[8]

However, for many terminally overwatered houseplants, the initial symptoms of waterlogging can resemble those due to drought. This is particularly true for flood-sensitive plants that show drooping of their leaves due to

(rather than wilting).

CO₂ concentration

CO₂ is vital for plant growth, as it is the substrate for photosynthesis. Plants take in CO₂ through

]

The concentration of

]

Wind

Wind has three very different effects on plants.[14]

• It affects the exchanges of mass (water evaporation, CO₂) and of energy (heat) between the plant and the atmosphere by renewing the air at the contact with the leaves (convection).
• It is sensed as a signal driving a wind-acclimation syndrome by the plant known as thigmomorphogenesis, leading to modified growth and development and eventually to wind hardening.
• Its drag force can damage the plant (leaf abrasion, wind ruptures in branches and stems and windthrows and toppling in trees and lodging in crops).^[15]

Exchange of mass and energy

Wind influences the way leaves regulate moisture, heat, and carbon dioxide. When no wind is present, a layer of still air builds up around each leaf. This is known as the

Acclimation

Plants can sense the wind through the deformation of its tissues. This signal leads to inhibits the elongation and stimulates the radial expansion of their shoots, while increasing the development of their root system. This syndrome of responses known as thigmomorphogenesis results in shorter, stockier plants with strengthened stems, as well as to an improved anchorage.^[17] It was once believed that this occurs mostly in very windy areas. But it has been found that it happens even in areas with moderate winds, so that wind-induced signal were found to be a major ecological factor.^[14][18]

Trees have a particularly well-developed capacity to reinforce their trunks when exposed to wind. From the practical side, this realisation prompted arboriculturalists in the UK in the 1960s to move away from the practice of staking young

Wind damage

Wind can damage most of the organs of the plants. Leaf abrasion (due to the rubbing of leaves and branches or to the effect of airborne particles such as sand) and leaf of branch breakage are rather common phenomena, that plants have to accommodate. In the more extreme cases, plants can be mortally damaged or uprooted by wind. This has been a major selective pressure acting over terrestrial plants.[20] Nowadays, it is one of the major threatening for agriculture and forestry even in temperate zones.^[14] It is worse for agriculture in hurricane-prone regions, such as the banana-growing Windward Islands in the Caribbean.^[21]

When this type of disturbance occurs in natural systems, the only solution is to ensure that there is an adequate stock of seeds or seedlings to quickly take the place of the mature plants that have been lost- although, in many cases, a successional stage will be needed before the ecosystem can be restored to its former state.

Animals

Humans

]

Thermoregulation

To achieve this, the body alters three main things to achieve a constant, normal body temperature:

• Heat transfer to the
  epidermis
• The rate of evaporation
• The rate of heat production

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 is physiologically combated in four ways:

, 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

. 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.

Altitude

Extreme temperatures are not the only obstacles that humans face.

also pose serious physiological challenges on the body. Some of these effects are reduced arterial ${\displaystyle P_{{\mathrm {O} }_{2}}}$, the rebalancing of the ]

Environmental factors can play a huge role in the human body's fight for homeostasis. However, humans have found ways to adapt, both physiologically and tangibly.^{[citation needed]}

Scientists

]

Hermann Rahn (1912–1990) was an early leader in the field of environmental physiology. Starting out in the field of zoology with a Ph.D. from University of Rochester (1933), Rahn began teaching physiology at the University of Rochester in 1941. It is 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 the basis for much of Rahn's future work. Rahn's research into applications of this diagram led 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.^{[citation needed]}

See also

References

Further reading

• Bennett, A. F.; C. Lowe (2005). "The academic genealogy of George A. Bartholomew".
  PMID 21676766
  .
• Bradshaw, Sidney Donald (2003). Vertebrate ecophysiology: an introduction to its principles and applications. Cambridge, U.K.: Cambridge University Press. p. xi + 287 pp.
  ISBN 978-0-521-81797-4
  .
• Calow, P. (1987). Evolutionary physiological ecology. Cambridge: Cambridge University Press. p. 239 pp.
  ISBN 978-0-521-32058-0
  .
• Karasov, W. H.; C. Martinez del Rio (2007). Physiological ecology: how animals process energy, nutrients, and toxins. Princeton, NJ: Princeton University Press. p. xv + 741 pp.
  ISBN 978-0-691-07453-5
  .
• Lambers, H. (1998). Plant physiological ecology. New York: Springer-Verlag.
  ISBN 978-0-387-98326-4
  .
• Larcher, W. (2001). Physiological plant ecology (4th ed.). Springer.
  ISBN 978-3-540-43516-7
  .
• McNab, B. K. (2002). The physiological ecology of vertebrates: a view from energetics. Ithaca and London: Comstock Publishing Associates. xxvii + 576 pp.
  ISBN 978-0-8014-3913-1
  .
• Sibly, R. M.; P. Calow (1986). Physiological ecology of animals: an evolutionary approach. Oxford: Blackwell Scientific Publications. p. 179 pp.
  ISBN 978-0-632-01494-1
  .
• Spicer, J. I., and K. J. Gaston. 1999. Physiological diversity and its ecological implications. Blackwell Science, Oxford, U.K. x + 241 pp.
• Tracy, C. R.; J. S. Turner (1982). "What is physiological ecology?".
  S2CID 86354445
  .. Definitions and Opinions by: G. A. Bartholomew, A. F. Bennett, W. D. Billings, B. F. Chabot, D. M. Gates, B. Heinrich, R. B. Huey, D. H. Janzen, J. R. King, P. A. McClure, B. K. McNab, P. C. Miller, P. S. Nobel, B. R. Strain.

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