The following is an annotated bibliography of some books and articles regarding respiration and evaporation in plants. In the paper, contribution of the said is discussed and how it affects climate of an area looked at.
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After approximately 4 million years of existence, the world’s water supplies are not near depletion as Bendtner (2007) says. The hydrological cycle responsible for recycling of water has been shown to keep water, as an essential product for all organisms, be it plants or animals available for use. The hydrological cycle draws its strength from the various elements of weather in the cycle such as such rainfall and other form of precipitation. At the center of this cycle is also evaporation of water from the ground and from plants hereby called transpiration. These two processes are responsible for impacting the climatic globally and from region to region. Apart from this aspect, the existence of plants by the mere fact that they respire has its own way of contributing to climatic change indirectly.
According to a 2006 United Nations Environmental Program (UNEP) report, human or anthropogenic activities have continued to interrupt with ecological balance, which has impacted in various ways to the climate. In realization of this, man is trying to make all possible efforts in reversing the situation as research has shown that such prolonged harmful activities will make the earth inhabitable due to intolerable climatic conditions. As a result, a lot of research has been extended in this direction with a lot of very positive results. The role-played by plants and vegetation cover has been identified with particular concern on evaporation process on earth and transpiration process in plants taking center stage. To fully understand the role these processes play, this paper discusses the roles played by evaporation and transpiration impacting or influencing climate directly and indirectly.
Evaporation and transpiration have been, as said above responsible for keeping water within the reach to all organisms and a major component in climate. Due to their similar roles, we have evapotranspiration. The word in coined from combining evaporation and transpiration to make it the process unique to the evaporation resulting from plants (Dmitri, 2006). The process revolves around the absorption of water and minerals from the soil by plants through their roots and through the photosynthesis process breakdown carbons to produce oxygen as a byproduct. In the absence of light the process is somehow reversed with oxygen being taken in from the atmosphere and carbon dioxide released back into the atmosphere.
Moisture in form of water vapor is lost by plants through their stomata (small openings) found on their leaves. The rate at which this evaporation takes place is again determined by prevailing weather conditions. i.e. in high humidity the rate is low and in low humidity the rate is high. In addition to this, there has to a relative humidity aspect. The higher the relativity, the higher the rate of evaporation. This thus explains transpiration as a process by which water moves from the ground back into the atmosphere using plants as a medium. On the other hand, evaporation is the change of water from a liquid form to a gaseous form. For the change to take place, there has to heat.
The rate of evapotraspiration is determined by a number of factors. Therefore, the presence or absence of these factors contributes significantly in determining the degree of influence it will have on the climate (Pidwirny, 2006).
- Solar energy availability as the core driver of the whole process:- Heat energy from the sun is responsible fro transforming water from a liquid state to a gaseous state. One gram of liquid water requires about 600 calories of heat energy to change into water vapor.
- The humidity gradient”- The difference in humidity levels determines the rate of evapotrnspiration with the rate being highest in dry and arid areas.
- Air turbulence and the speed of wind. Wind increases the potential for evapotranspiration by increasing humidity gradient (Russell, 2004). The same way that clothes dry more quickly on a windy day is the same way that evapotranspiration is high in plants and on the surface. The idea is that wind removes saturated air adjacent to an evaporating surface and creates humidity gradient by bringing in drier air.
- Availability of water. Evapotranspiration cannot occur if water is not available on the earth surface and to plants.
In the era of global warming, plants have been identified as on e of the major ways by which to curb the harmful effect. Global warming has been attributed to the increased production of green house gases, which have led to the altering of climate with global temperatures on the increase. While these greenhouses have no direct impact in generating heat that alters global temperatures, their relationship or their behavior in the presence of light makes all the difference (Lisa and Melvin, 2005). Researchers have informed us that human contribution to climatic change in this case, global warming remains very minimal as the change in temperature seems to have a natural pattern as it is also happening in other planets such as Mars.
In our planet earth, glaciers are melting pretty first, desertification is encroaching fast in rather agriculturally productive areas making life difficult for farmers and everyone as the harsh climatic conditions are very hostile for human habitation.
In response to this deterioration of our climatic environment, increased vegetation cover has been observed to reduce the impact.
Plants absorb the excessive carbon dioxide in the atmosphere and convert it to oxygen. Oxygen as a gas has no radiation effect like CO2, which contributes to climatic changes. In fact Bethan (2007) says that in the last 20 years, global temperature has risen by around 1 Celsius. For the better part of researches dedicated to finding out the relationship between climate and vegetation, they have concentrated on finding out the effect of climatic change on plant cover not the vise versa.
Evatranspiration has on the other hand shown that it contributes positively by increasing humidity levels in the atmosphere. The fact that plants through their leaves loose water to the atmosphere has a direct contribution on the climate. The greater the plant cover then the greater the levels of humidity. Humidity on the other hand has shown that it impacts on the amounts of clouds in the atmosphere. Logan (2003) says that on one hand clouds will “blanket” the atmosphere and insulate it locking away direct heating from the sun on earth’s atmosphere.
Another contribution of transpiration and evaporation on climate is highlighted by Kelly et al (2003), although controversial is that increased evapotranspiration leads to increased density of air especially around heavy vegetation areas and large water bodies. As a result of the increased air density, movement of air is limited leading to weak winds, which can at times be destructive. In addition, heavy plants cover acts as windbreakers. The authors support their argument by quoting the destruction caused by strong winds in areas with relatively lower vegetation cover, hence lower evapotranspiration rates. This argument is refuted by Vivian (2006) who says that there is no direct empirical evidence to support the argument saying that the presence of strong winds in areas with less vegetation is due to other climatic factors other than the amount of water vapor in the atmosphere courtesy of evaporation and transpiration.
Research has shown that transpiration from plants represents approximately 0.7 of Earths evapotranspiration. Transpiration thus utilizes 40% of Earth surface net radiation as a latent heat (Peter, Major, 2003). This indicates that evapotranspiration has its own way of ensuring cool climatic conditions by absorbing the excessive heat energy thus a sure way of regulating climatic conditions.
The Going green campaigns have in the recent times, according to Graham (2006) faced hostility from very determined sources leaving the world at a dilemma. The cause of this shift in direction into campaigning against excessive tree planting as the ultimate solution to climatic changes and global warming was as a result of some scientific findings done in the UK in 2006. In an article titled “Global warming: blame it all on the forests” in The Guardian, it was reported that plants contributed about 30% of methane gas, which has a green house in the atmosphere.
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Russell further explains the above situation in giving a relationship of how plants relate with the environment. Methane gas radiates a lot of heat that contributes to global warming and the eventual climatic change. Though this may appear to have little significance in this topic, it relates to our discussion in that transpiration as a vital process in plants carries out function of injecting the harmful gas into the atmosphere. In addition, the increased global temperatures will increase the rate of evaporation from the plants.
Plants absorb water from the ground and use it in transporting nutrients and eventually lost in the air through respiration as a component process of transpiration. The water vapor released into the atmosphere, like all forms of water vapor rises up in the air, cools and condenses to form clouds. Before the water condenses to form clouds, it impacts heavily on the climate as it rises up. Research has shown that water vapor has a green house effect and in fact the largest contributor global warming estimated to account for 36%-66% of the total effect. The cycle here is continuous as highlighted by Lisa and Melvin, (2005). They say that the resultant warm climate will lead to more warming as hot air has the capacity to hold more water vapor.
The effects of evapotranspiration on the global climate seem to weigh more heavily on the positive side. This would thus mean that the human population should work hand in hand in ensuring there is more plant cover on the planet to ensure that favorable climatic conditions are restored. On the other hand, these activities are limited by the various factors that determine the level of evapotranspiration.
Bendtner, W. Introduction to climatology, New York: Prentice Hall
Dmitri, H. Official mechanism for implementing environmental impact analysis in Africa, Pretoria: Makurdi, 2006.
Graham, D. Environmental problems and their management: the role of the government and citizens, Ajeam-Agee journal, Vol 23, No. 8, 2002.
Kelly, Brandon, et al, Population, Human Resources, Health, and the Environment: Getting the Balance Right, Review, Vol. 342, No. 9, 2003.
Lisa, Y. and Melvin, J. Environmental challenges emphasizing increased medical care, Lagos: Ikibe, 2005.
Logan, C. Industrialization and environmental pollution in Europe, Science journal Vol. 1121, No.6, 2003.
Oliver, J. and Hidore, J. Climatology-An Atmospheric Science 2nd edition, London: Pearson.
Peter, M. and Major, L. Effective Survival Measures for Environmental and Ecological Hazards in Nigeria, 2003, pg 23.
Pidwirny, M. Fundamentals of Physical Geography, 2nd Edition, London: Penguin, 2006.
Rudolf, O. Deserts and desertification: Causes and Effects, Boston: Wesley, 2003.
Russell, B. The symbiotic relationship between plants and climate, Michigan University Press, 2004.
United Nations University Newsletter, 7 (2), 9, Tokyo, Japan, 2003.
UNEP, Fresh-Water Pollution, UNEP /GEMS Environment Library, No. 6, UNEP, Nairobi, Kenya, 2006): World Development Report 2003, New York, Oxford University Press, 2000. World Bank Pollution Prevention and Abatement Handbook, Toward Cleaner Production.