Causes And Effects Of Drought Stress Environmental Sciences Essay

Causes And Effects Of Drought Stress Environmental Sciences EssayDrought can be defined as the absence of rainfall and water or irrigation for a current of time sufficient to deplete s oil colour moisture and injure limits (Plantlifeonline.net, 2007). In short, drought is a period of time without rainfall. The drought is one of the most serious global issues for agriculture field and need to harsh precaution need to be taken immediately. Four-tenths of the worlds sylvan land lies in arid or semi-arid regions especially in Africa.Meanwhile, drought mark is defined as effects of some period of plants that involve plant water relationships. According to Farooq et al. (2008) drought tense up reduces and decreases the size of plants paging, extension of stem and proliferation of roots that disturbs plant water relations and reduces water-use efficiency. While ForestryNepal(n.d.) defined that drought tenseness occurs when the avai testing groundle water in the soil is reduced andatm ospheric conditions cause continuous loss of water by transpiration orevaporation. Drought stress adjustment can be found in almost all plants but its extent variesfrom species to species and even within species. It is characterized byreduction of water content, diminished leaf water potential and turgor loss, closure,nutrient metabolism and evolution promoters. Plants display a variety of physiological and biochemical responses at cellular and whole organism levels towards rife drought stress, thus making it a complex phenomenon. Based on Bishop(n.d) report, many variables play a part in reaching drought conditions, these imply lack of inhering rainfall, types of soil, air temperature, humidity, conditions of wind, impression of sun, and also plant type or root depth that increase pant water loss. Drought stress can affect the growth of plants in various ways.One of the effects is the priming on seed performance of several plants due to lack of natural rainfall. For example o f plant that can be affected from this problem is Canola plant (Brassica napus L.). Based on the report of Mohammadi and Amiri(2010) , Canola plant is one of the most important oil seed crops which its production has been notably extended during recent years in Iran and due to lack of rainfall at planting time and the seeds are gross planted in seedbeds having unfavorable moisture. The drought stress is responsible for both crushing and delayed seed germination and seedling establishment of Canola. Consequently, this stress adversely affects growth and development of crop and also results into low Canola yield. There is a decrease in water uptake both during imbibition and seedling establishment under this stress condition. Tutorvista(n.d.) stated that imbibitions process is the phenomenon of adsorption of water by the solid particles of a substance without forming a solution. Furthermore, inhibition of radicle also occurs due to the effect of stress condition. The inhibition eme rgence is mainly because of a decrease in water potential gradient between the external environment and the seeds. In addition, the seed priming has been successfully proved and demonstrated to improve germination and emergence in seeds of many crops and plants, especially under stress conditions. The seed priming is a technique that starts the germination process in the lab or plant. Moreover, the basic chemical reactions or framework for the seed to germinate and for the process to occur efficiently in the lab or plant, high moisture and ideal temperature condition are needed (Hariss, n.d.).Secondly is that the drought stress can affects the photosynthetic rate and leaf gun exchange of plants. Siddique et al. (1998) reported that, drought stress effects on photosynthetic rate and leaf gas exchange characteristics. The experiment had been done to four pale yellow (Triticum aestivum L.) cultivars which were evaluated under semi-controlled conditions. According to Siddiques observat ion, four cultivars which were Kanchan, Sonalika, Kalyansona, and C306, grown in pots and were subjected to four levels of water stress. However, cultivars that showed the highest photosynthesis rates both at vegetative and at anthesis among others is the Kalyansona. They had concluded that the exposure of plants to drought stress led to noticeable decrease in photosynthesis rate, stomatal conductance and mesophyll conductance and a concomitant increase in intercellular CO2 concentration. The plants that were subjected to drought at the early vegetative stage displayed similar physiological characters subsequently under well-watered conditions as compared with control. Therefore, the photosynthesis rates decreased with decrease in stomatal conductance, but a weak relationship between them implied that non-stomatal limitations to photosynthesis might have been in operation. The involvement of CO2 concentration and assimilation was described in Farooq et al. (2008) report. The CO2assi milation by the leaves is reduced mainly by the closure of the stomata, damaged the membrane and disturbed activity of various enzymes in the plants, especially those of O2fixation and adenosine triphosphate(ATP) synthesis. Moreover, the enhancement of metabolite flux through the photorespiratory pathway had increased the oxidative load on the tissues as both processes generate reactive atomic number 8 species. The damage and injury caused by reactive oxygen species to biological macromolecules under drought stress is among the major deterrents to growth.