Abiotic stress

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Abiotic stress is defined as the negative impact of non-living factors on the living organisms in a specific environment.[1] The non-living variable must influence the environment beyond its normal range of variation to adversely affect the population performance or individual physiology of the organism in a significant way.[2] Whereas a biotic stress would include such living disturbances as fungi or harmful insects, abiotic stress factors, or stressors, are naturally occurring, often intangible, factors such as intense sunlight or wind that may cause harm to the plants and animals in the area affected. Abiotic stress is essentially unavoidable. Abiotic stress affects animals, but plants are especially dependent on environmental factors, so it is particularly constraining. Abiotic stress is the most harmful factor concerning the growth and productivity of crops worldwide.[3] Research has also shown that abiotic stressors are at their most harmful when they occur together, in combinations of abiotic stress factors.[4]

Contents

[edit] Examples of Abiotic Stress

Abiotic stress comes in many forms. The most common of the stressors are the easiest for people to identify, but there are many other, less recognizable abiotic stress factors which affect environments constantly. The most basic stressors include: high winds, extreme temperatures, drought, flood, and other natural disasters, such as tornados and wildfires. The lesser-known stressors generally occur on a smaller scale and so are less noticeable, but they include: poor edaphic conditions like rock content and pH, high radiation, compaction, contamination, and other, highly specific conditions like rapid rehydration during seed germination.[5]

[edit] Effects of Abiotic Stress

Abiotic stress, as a natural part of every ecosystem, will affect organisms in a variety of ways. Although these effects may be either beneficial or detrimental, the location of the area is crucial in determining the extent of the impact that abiotic stress will have. The higher the latitude of the area affected, the greater the impact of abiotic stress will be on that area. So, a taiga or boreal forest is at the mercy of whatever abiotic stress factors may come along, while tropical zones are much less susceptible to such stressors.[6]

[edit] Benefits

Just as it is hard to imagine stress as a positive point in one’s life, it is difficult to find a situation where abiotic stress plays a constructive role in an ecosystem. It is not that those situations do not exist, however. One example is in natural wildfires. While letting forests burn near housing establishments is generally considered a human safety hazard, it is actually productive for the ecosystem to burn out every once in a while so that new organisms can begin to grow and thrive. Even though it is healthy for an ecosystem, a wildfire can still be considered an abiotic stressor, because it puts an obvious stress on individual organisms within the area. Every tree that is scorched and each bird nest that is devoured is a sign of the abiotic stress. On the larger scale, though, natural wildfires are positive manifestations of abiotic stress.[7] What also needs to be taken into account when looking for benefits of abiotic stress, is that one phenomenon may not affect an entire ecosystem in the same way. While a flood will kill most plants living low on the ground in a certain area, if there is rice there, it will thrive in the wet conditions. Another example of this is in, phytoplankton and zooplankton. The same types of conditions are usually considered stressful for these two types of organisms. They act very similarly when exposed to ultraviolet light and most toxins, but at elevated temperatures the phytoplankton reacts negatively, while the thermophilic zooplankton reacts positively to the increase in temperature. The two may be living in the same environment, but an increase in temperature of the area would prove stressful only for one of the organisms.[2] Lastly, abiotic stress has enabled species to grow, develop, and evolve, furthering natural selection as it picks out the weakest of a group of organisms. Both plants and animals have evolved mechanisms allowing them to survive extremes.[8]

[edit] Detriments

The most obvious detriment concerning abiotic stress involves farming. It has been claimed by one study that abiotic stress causes the most crop loss of any other factor and that most major crops are reduced in their yield by more than 50% from their potential yield.[9] It has also been speculated that this yield reduction will only worsen with the dramatic climate changes expected in the future.[10] Because abiotic stress is widely considered a detrimental effect, the research on this branch of the issue is extensive. For more information on the harmful effects of abiotic stress, see the sections below on plants and animals.

[edit] In Plants

A plant’s first line of defense against abiotic stress is in its roots. If the soil holding the plant is healthy and biologically diverse, the plant will have a higher chance of surviving stressful conditions.[7] Facilitation, or the positive interactions between different species of plants, is an intricate web of association in a natural environment. It is how plants work together. In areas of high stress, the level of facilitation is especially high as well. This could possibly be because the plants need a stronger network to survive in a harsher environment, so their interactions between species, such as cross-pollination or mutualistic actions, become more common to coop with the severity of their habitat.[11] This facilitation will not go so far as to protect an entire species, however. For example, cold weather crops like rye, oats, wheat, and apples are expected to decline by about 15% in the next fifty years and strawberries will drop as much as 32% simply because of projected climate changes of a few degrees. Plants are extremely sensitive to such changes, and do not generally adapt quickly.[10] Plants also adapt very differently from one another, even from a plant living in the same area. When a group of different plant species was prompted by a variety of different stress signals, such as drought or cold, each plant responded uniquely. Hardly any of the responses were similar, even though the plants had become accustomed to the exact same home environment.[4]

[edit] Plant Breeding

Because individual plants react so differently to similar abiotic stress factors, it can be difficult to breed a species for more than one resilient trait at a time, but that is exactly what plant breeders are looking to do. For example, rice has a high tolerance to flooded areas and soil salinity, but is sensitive to cold, so each trait must be isolated and magnified when looking to produce new plants with the best of all strengths. This idea has worked for rice. Rice grown created to be grown in cold weather now lives in Nepal and Bangladesh.[10] One study has suggested the idea of exposing plants to stress factors to increase their resilience. This will actually activate a stress-response signal in the plant, so it will be more able to respond quickly and efficiently in case of a real abiotic stressor.[4] One important note with plant breeding is that when the new crops are being created, a person should keep in mind what crops are already living in the area. If those crops, and their traits, are ignored, then the new variety might actually be a step backward. Traditional values and practices should be allowed to filter into the planting of whatever newly resilient seed is developed. That way, the new crop will best fit the natural landscape, as the old one did, and will have adapted more quickly to whatever changing abiotic factors are present.[10]


[edit] In Animals

For animals, the most stressful of all the abiotic stressors is heat. This is because many species are unable to regulate their internal body temperature. Even in the species that are able to regulate their own temperature, it is not always a completely accurate system. Temperature determines metabolic rates, heart rates, and other very important factors within the bodies of animals, so an extreme temperature change can easily distress the animal’s body. Animals can respond to extreme heat, for example, through natural heat acclimation or by burrowing into the ground to find a cooler space.[8] It is also possible to see in animals that a high genetic diversity is beneficial in providing resiliency against harsh abiotic stressors. This acts as a sort of stock room when a species is plagued by the perils of natural selection. A variety of galling insects are among the most specialized and diverse herbivores on the planet, and their extensive protections against abiotic stress factors have helped the insect in gaining that position of honor.[12]


[edit] In Endangered Species

Biodiversity is determined by many things, and one of them is abiotic stress. If an environment is highly stressful, biodiversity tends to be low. If abiotic stress does not have a strong presence in an area, the biodiversity will be much higher.[7] This idea leads into the understanding of how abiotic stress and endangered species are related. It has been observed through a variety of environments that as the level of abiotic stress increases, the number of species decreases.[6] This means that species are more likely to become population threatened, endangered, and even extinct, when and where abiotic stress is especially harsh.


[edit] References

  1. ^ Abiotic Stress. Biology Online. Retrieved on 2008-05-04.
  2. ^ a b Vinebrooke, Rolf D. et al. “Impacts of multiple stressors on biodiversity and ecosystem functioning: the role of species co-tolerance.” OIKOS 104: 451– 457, 2004.
  3. ^ Gao, Ji-Ping, et al. “Understanding Abiotic Stress Tolerance Mechanisms: Recent Studies on Stress Response in Rice.” Journal of Integrative Plant Biology 49 (6): 742−750, 2007.
  4. ^ a b c Mittler, Ron. “Abiotic stress, the field environment and stress combination.” TRENDS in Plant Science 11(1): 15–19, 2006.
  5. ^ Palta, Jiwan P. and Farag, Karim. “Methods for enhancing plant health, protecting plants from biotic and abiotic stress related injuries and enhancing the recovery of plants injured as a result of such stresses.” United States Patent 7101828, September 2006.
  6. ^ a b Wolfe, A. “Patterns of biodiversity.” Ohio State University, 2007.
  7. ^ a b c Brussaard, Lijbert, Peter C. de Ruiter, and George G. Brown. “Soil biodiversity for agricultural sustainability.” Agriculture, Ecosystems and Environment 121: 233–244, 2007.
  8. ^ a b Roelofs, D. et al. “Functional ecological genomics to demonstrate general and specific responses to abiotic stress.” Functional Ecology 22: 8–18, 2008.
  9. ^ Wang, W., Vinocur, B. and Altman, A. “Plant responses to drought, salinity and extreme temperatures towards genetic engineering for stress tolerance.” Planta 218: 1-14, 2007.
  10. ^ a b c d Lane, A. and A. Jarvis. “Changes in Climate will modify the Geography of Crop Suitability: Agricultural Biodiversity can help with Adaptation.” eJournal 4(1): 1-12, 2007.
  11. ^ Maestre, Fernando T., Jordi Cortina, and Susana Bautista. “Mechanisms underlying the interaction between Pinus halepensis and the native late-successional shrub Pistacia lentiscus in a semi-arid plantation.” ECOGRAPHY 27: 776–786, 2007.
  12. ^ Goncalves-Alvim, Silmary J. and G. Wilson Fernandez. “Biodiversity of galling insects: historical, community and habitat effects in four neotropical savannas.” Biodiversity and Conservation 10: 79–98, 2001.