Ethnobotanical Leaflets 12: 553-56. 2008.
Global Warming and Stomatal Complex Types
Abdulrahaman, A. A.1 and Oladele, F. A.2
Department of Plant Biology
Ozone depletion and its ultimate effect, global warming are main concerns in climate change in the world today. The phrase ‘climate change’ is growing in preferred use to ‘global warming’ because it helps convey that there are changes in addition to rising temperatures. Accumulation of greenhouse gases in the atmosphere depleted the ozone layer and consequently causes global warming. Gases that trap heat in the atmosphere are often called greenhouse gases. That the Earth has warmed by 0.74oC over the last hundred years and that around 0.4oC of this warming has occurred since the 1970s is unequivocal fact that leaves little room for doubt that human activity is the primary driver of these changes (May, 2006). Among factors that emit the greenhouse gases into the atmosphere are burning of woods (fuel woods) and deforestation. Removal of plants on the surface of planet Earth is no doubt contributing greatly to the accumulation of greenhouse gases and thus the global warming.
World leaders, public health specialists, engineers, atmospheric chemists, hydrologists, quantum physicists, mathematicians, botanists, zoologists, have all being striving to stop further release of more greenhouse gases into the atmosphere, and in the occurrence of these gases, they are trying to purifying or cleansing them. One of the cleaners or purifiers that can be employed is stomata. Figures 1 to 8 showed different types of stomatal complex systems in some species of Amaranthus. Stomata are microscopic openings or pores located majorly on the abaxial or lower, and adaxial or upper surfaces of leaves of plants. Though sometimes, stomata are present on the stems, petioles and sepals but in very small number.
Meanwhile, plants have the ability to absorb carbondioxide for carbonxylation and subsequently for production of carbohydrates (especially by the tuberous plants) and for production of woods and fibres (by trees) through photosynthesis. Photosynthesis is the major process by which plants produced carbohydrates, and the major ingredient in this process is carbondioxide. Unfortunately, carbondioxide is one of the greenhouse gases (other examples include methane [CH4], nitrous oxide [N2O], fluorinated gases – hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride). The accumulation of these gases in the atmosphere strengthened the greenhouse effect, which occurs when the heat produced by the sun’s rays entering the atmosphere is retained, causing global warming. Some greenhouse gases such as carbondioxide occur naturally and are emitted to the atmosphere through natural processes and human activities. Other greenhouse gases (e.g. fluorinated gases) are created and emitted solely through human activities. About 99% carbondioxide used in photosynthesis is absorbed through stomata (lenticels and cuticles also absorb carbondioxide to lesser extent). Earlier studies by Carr and Carr (1990), Obiremi and Oladele (2001) and Oyeleke et al. (2004) had confirmed that the more the subsidiary cells surrounding the guard cells, the faster the opening of the stoma (i.e. pore between the two guard cells) and vice versa.
In relation with this, plants that possessed stomata with many subsidiary cells (e.g. tetracytic and anomocytic types) will play important role in reducing greenhouse gases especially carbondioxide. To proof this fact, Obiremi and Oladele (2001) and Oyeleke et al (2004) studied the relationship between the stomatal complex types and transpiration rate in some selected Citrus species and some afforestation tree species respectively. In both studies, stomatal complex types with many subsidiary cells transpired higher than those with less number. This translates to mean that the latter opens faster to allow carbon dioxide to enter the leaves and water vapour to escape to the atmosphere via the stomatal openings than the former. More over the other aspect of stomatal opening that favour water loss to the atmosphere (i.e. encouraging high rate of transpiration) is also advantageous by humidifying the atmospheric air.
However, to achieve reasonable atmospheric purification, plants with hypostomatic nature of the leaves (i.e. stomata being found or located on the abaxial surface only), lower frequency of stomata with many subsidiary cells (e.g. anisocytic, tetracytic and anomocytic), higher frequency of stomata with frequency of stomata with little subsidiary cells (e.g. cyclic, paracytic and diacytic), less heterogeneous composition of stomatal complex types, less stomatal density and index (i.e. less distribution of stomata on the surface of leaves), and lastly, probably occurrence of trichome (Figures 9 – 11) may be more suitable for afforestation in dry locations. Plants with opposite conditions of the above stomatal features may be more suitable for afforestation in wet environments. These conditions had earlier identified by Oyeleke et al. (2004) and AbdulRahaman and Oladele (2003; 2004).
AbdulRahaman, A. A. and
Oladele, F. A. (2003). Stomatal complex types, stomatal size, density and
index in some vegetable species in
AbdulRahaman, A. A. and Oladele, F. A. (2004). Types, density and frequency of trichomes in some Nigerian vegetable species. Nigerian Journal of Pure and Applied Science, 19; 1653-1658.
May, L. R. (2006). Securing a global future. New Scientist. p. 17.
Obiremi, E. O. and Oladele, F. A. (2001). Water-conserving stomatal systems in selected Citrus species. South African Journal of Botany, 67: 258-260.
Oyeleke, M. O., AbdulRahaman, A. A. and Oladele, F. A. (2004). Stomatal anatomy and transpiration rate in some afforestation tree species. Nigerian Society for Experimental Biology Journal, 4(2): 83-90.