The Effects of Environmental Stress Salinity on Acacia Seedling Emergence Species - Literature review Example

Acacia Name: Institution: Acacia Climate change and human activities continue to have immeasurable impact on the natural vegetation cover in the different parts of the world. Introduction of new crop species and economic-focused agriculture has particularly had great impact on the Australian vegetation and ecosystem. Such activities pose unfathomable threat to the natural ecosystems especially the extinction of some indigenous plant species. Vegetation clearance for commercial agriculture can be associated with increasing desertification in not only Australia but also other parts of the world. Agro forestry has emerged as a solution to the need to increase vegetation cover amidst the growing demand for farming land. The concept of agroforestry focuses on mitigating the impact of vegetation clearance associated with economic farming on the climate change. Agroforestry provides options for minimizing the impact of rapidly expanding agricultural systems that not only threaten the existence of the natural vegetation but also climate change (Lefroy & Stirzaker, 1999). As such, the agroforestry practice enhances the adaptability and sustainability of agricultural systems. However, the continued expansion of such agricultural systems poses other environmental challenges such as increased soil salinity and overall sustainability of the Australian environment. Soil salinity forms one of the environmental stress factors which impact negatively on productivity and growth of plants (Australian Government, 2013). According Thrail, Bever and Slattery (2008), continued clearance of deep rooted perennial plants in Australia has contributed to the increase in dryland salinity, a phenomenon that threatens the growth and productivity of other plant species in such areas. This paper explores the adaptability of different Acacia plant species to environmental stress factors such as soil salinity as one of the critical step in the future re-vegetation efforts in South Australia. This would be critical in addressing problems arising from the growing introduction of water-use efficiency plants and the need to ensure expansion and the long-term sustainability of the agriculture industry in Australia. Similar to other plant species, the growth of different acacia species is influenced several environmental factors such as soil salinity levels, soil Ph, water availability, and soil toxicity. According to Ramoliya and Pandey (2002), previous studies on the adaptability of the different acacia plant species have demonstrated variations in the abundance and diversity of some species in relation to the soil chemistry and other physical environmental factors. The Effects of Environmental Stress Salinity On Acacia Seedling Emergence Species Previous studies have shown that salinity as an environmental stress factor affects seedling emergency, growth and the survival of the acacia plant. In this case, different acacia plant species have shown diverse seedling emergency, growth, and survival in different soil salinity levels. In a study aimed at investigating the effects different salinity levels on the seedling emergence of Acacia nilotica species, results revealed lack of seed emergence in soil with salinity levels above 12.2 ds m-1 (Ramoliya & Pandey, 2002). According to Ramoliya and Pandey (2002), further studies have shown a clear association between high soil salinity and retardation of germination and growth of seedling. At the same time, different plant species have shown variations in their tolerance to salinity levels hence the need to investigate the variations in salts tolerance among the various acacia. Understanding of the salinity tolerance for different acacia plant species emerges as a crucial step in screening of acacia species for re-vegetation of the south-west Australia as well as other areas that continue to face the threat of desertification (Thrall, Bever & Slattery, 2008). Acacia nilotica emerges as one of the acacia plant species that can be studied to determine its suitability in growing in the saline and drylands of southwest Australia. Acacia nilota (Mimosaceae) is the dominant vegetation covering the vast area of the Kutch desert of Gujarat State in India. Kutch desert is one of the deserts known to have high levels of salinity (Ramoliya & Pandey, 2002). A. nilotica draws significant interest from researcher because of its ability to adapt well in both saline and arid areas as well as in non-saline and marginal semi-arid environments. According to Ramoliya & Pandey (2002), A. nilotica has been shown to have high drought tolerance in addition to its ability to reproduce naturally through seed germination, a phenomenon that makes the plant effective for re-vegetation and agroforestry in arid and semi-arid areas. The ability of the acacia plant to survive in high saline environment can be attributed to its ability to tolerate high salt concentrations at the seed germination phase. However, in extremely high saline conditions, seed germination can hindered due to changes in osmotic pressure changes and negative effects on protein hydrolysis due to inactivation of responsible enzyme. Other physiological adaptation properties that enable the plant to grow and survive in relative high saline and limited water environments include its tendency for rapid root development and penetration into deeper into the soil as well as production of high volume of roots. Such properties enable the plant to survive through the dry spells experienced in semi-arid regions. During seed germination, the A. nilotica use the available moisture to penetrate and extent its root system into the deep layer of the soil, a phenomenon that enable the plant to survive throughout the dry and wet seasons. Acacia saligna on of the dominant acacia species covering a vast area of south west of western Australia has shown high levels adaptability to the soil and climate factors characteristic of the region. The plant has sub species adapted for growth in different areas of the region with the most dominant subspecies covering the Avon Wheatbelt region the geographical area while the other subspecies grow in areas such as Swan Coastal Plain of the Perth region, Jarrah forests of the southwest and areas near Badgingara north of Perth. The adaptability of the A. saligna is attributed to several unique physiological adaptations including its fast growing and its nitrogen-fixing properties (Chapin, Sala & Huber-Sannwald, 2001). The species is considered have a moderate species has shown the potential to grow and adapt to areas receiving as low as 200mm rainfall per annum as well as survive well in sandy soils and poor soils such as those found in mine sites. Although, in some cases the species has been treated as weed, it has several benefits including wood salt tolerant and can grow in a wide range of soils including acidic and alkaline soils (Bui, Thornhill & Miller, 2014). The plant has other benefits to the communities around such the use for composite wood products and stock fodder. The species can survive high to non-saline soils as well as soils with extremely high acidity. Such properties have emerged as critical in the screening the plant for use as re-vegetation or agroforestry purpose. Another acacia species that has proven adaptive to the southwest Australian climatic and other physical factors is the Acacia brachypoda commonly known as Western Wattle or the Chinocup wattle. Their taxonomy places them in the family Mimosaceae (McCarthy, Wilson, Orchard & George, 2001). It is an abundant genus with The genus of Acacia (wattle) is one of the dominant components of Australia’s vegetation. approximately 1350 species around the world that 1000 of those species have been recorded more than 300 species are trees with a height more than five meters tall in Australia (Maslin, Miller, & Seigler, 2003; Midgley & Turnbull, 2003). Additionally, Acacia species in south-west Australia accounts for more than 60 percent of Acacia species in Australia. Acacias are necessary for ecosystem processes such as nitrogen fixing and carbon dioxide reduction. They also provide food, industry wood production, and raw materials for construction (Midgley & Turnbull, 2003). The acacia species is adapted to low-lying, winter-wet swamps and can grow in a wide range of soils including sandy soil, sandy loam, and sandy clay soil. Despite its adaptability to the southwest Australia region, it faces significant threat from increasing salinity and waterlogging. Western Wheatbelt Wattle prefers low-lying and salty areas but its moderate tolerance to high levels of salinity exposes it to the threat of rising salinity (McCarthy, Wilson, Orchard & George, 2001). As such, it is important to understand its germplasm to screen it for only areas that have moderate salinity level. As discussed, high levels of salinity have adverse effects on the germination, growth and survival of some acacia species and such screening is necessary to establish species that can survive the rising salinity levels and waterlogging. On the other hand, Acacia Cyclops, one of the acacia species that grow in the Southwest Australia has shown a germplasm that demonstrate its adaptation to the climate and physical factors in the region. The species has shown preference for coastal sand dunes where it emerges as the dominant vegetation in such areas. The germplasm of Acacia Cyclops shows suggests that the species can tolerate dry environments and salty soils. The species grows well in sandy soils and can survive weed and wind, properties that make it appropriate for dune stabilization. The plant can tolerate changing salinity levels, salt sprays and stand the wind and sandblast thus making it ideal for re-vegetation along the coastal lines(McCarthy, Wilson, Orchard & George, 2001). The species spreads fast due to the means of dispersion in which birds play a critical role in spreading the plant even into indigenous vegetation. The species remains a challenge for farmers practicing agroforestry because of its weedy nature and tendency to spread fast, a phenomenon that makes it difficult to clear the plant. In addition, the continued spread of the species is guarantee by the ability of its seeds to remain viable in the soil for several years hence the plant to escape the extinction threat posed by natural fires. The species can grow on drier soils such as sand dunes, a factor that makes the species appropriate for reclamation of arid and semi-arid areas. Threats Posed by the Expansion of the Acacia Vegetation Despite the numerous conservation benefits associated with the introduction of different acacia species in Australia, there is need to screen the germsplam of the various species to identify threats posed by some of the species. Some of the species have emerged as a major threat to the concept of agroforestry with some becoming invasive. Some of the germssplam characteristics such as rapid growth, and dispersion, and effective adaptability to soil and climate has resulted into some of the species becoming invasive with negative implications on the indigenous plants or vegetation (Craig, Bell & Atkins, 1990). Some of the species have become invaders of the native ecosystem thus threatening the existing ecosystems in some parts. High seedling species have resulted into densities or dense thickets under parent trees and a build-up affects native vegetation by inhibiting seedling establishment with consequent reduction in growth of native species. Acacia saligna species has particularly been identified with high potential for agroforestry for the southern Australia but the main challenge posed by the species revolves around its high weed risk. However, according to Nuberg, George and Reid (2009), further research has shown that the high weed risk associated with the species can be mitigated through the use non-suckering strains. In this case, understanding of the species germsplam can assist in the screening of non-suckering strains of the species for agroforestry to minimize the negative effect of weedy characteristic of the A. saligna. In other incidences, the expansion of the acacia vegetation in Australia has been associated with increasing salinity levels that threaten the survival of other plants especially in agroforestry (Nuberg, George & Reid, 2009). As such, farmers or conservation agencies promoting agroforestry as a strategy to re-vegetation of areas deforested areas. Although, species with long-lived soil seedbank ensure that such species survive harsh situations such as forest fires, they cause a lot of agony to farmers practicing agroforestry and as such, germsplam would play a critical role in minimizing such negative effects (Nuberg, George & Reid, 2009). On the other hand, germsplasm emerges as a necessity in screening species that suit different soil qualities and water availability. This is because some species such as A. saligna have demonstrated the ability to grow fast and survive in saline and waterlogged clay soils while other species have been shown to be threatened by the increasing salinity and waterlogging (Dell, Xu & Thu, n.d). In conclusion, the study of germsplam of different acacia species would play a critical role in screening acacia species best adapted for the Southwest Australia and for the agroforestry. References Australian Government. (2013). Our natural environment.Retrieved fromhttp://www.australia.gov.au/about-australia/our-country/our-natural-environment Bui, E., Thornhill, A & Miller T. (2014). Salt-and alkaline –tolerance are linked in Acacia. Biology Letter., 10. Retrieved fromhttp://rsbl.royalsocietypublishing.org/content/roybiolett/10/7/20140278.full.pdf Chapin, F., Sala, O & Huber-Sannwald, E. (2001). Global biodiversity in a changing environment: Scenarios for the 21st Century. London: Springer Science & Business Media. Craig, G., Bell, DT & Atkins, CA. (1990).Response to salt and waterlogging stress of ten texa of Acacia selected from natural saline areas of Australia. Australian Journal of Botany, 36(6), 619-630. Dell, B., Xu, D & Thu, P. (n.d). Managing threats to the health of tree plantations in Asia. Sustainable Ecosystems Research Institute. Retrieved fromhttp://cdn.intechopen.com/pdfs-wm/35407.pdf Lefroy, E & Stirzaker, R. (1999). 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