留学生Essay写作—植物生长的环境因素

http:/www.hotessay.net/ 留学生论文专业定制代写网站留学生Essay写作植物生长的环境因素AbstractDifferent environmental conditions contribute to the limitations of plant growth.Salts are common and a natural constituent of all soils.Normally,salts are present in low amounts in top soil and plant growth is not affected.However,accumulation of salts,through natural means or mans activities,can cause plant growth problems and result in poor growth or death of plants.Considering that Bermuda is such a small island,farmerscrops are constantly being exposed to salt spray.Therefore,there must be a saline threshold for the various crops.Bermuda is famous for The Bermuda Yellow Onion,therefore I felt it was appropriate to investigate The Salinity Tolerance of the Bermuda Yellow Onion.The objective of this study is to find out if the Bermuda Yellow Onion has a saline threshold,and if so what is this saline limit.To examine this question,I have constructed several small experiments,including the Saline Affect on Biomass,Germination Rate,Onion Growth,and the Water Content in Soil after Plant Growth.Throughout this investigation,I found that salinity effects both germination and overall growth of the Bermuda Yellow Onion,decreasing the yield percentage produced.The appearance of all plants grown in saline solutions are recognized as an effect of salt stress;poor germination and establishment,reduced plant vigour and stunted growth,smaller than normal leaves,slightly yellowing leaves,and a burnt appearance on tips of leaves.All experiments carried out show that salinity has an affect on the osmotic ability of both seed and plant,which has an effect on other plant functions such as photosynthesis and transpiration.Without the plant able to function effectively nor efficiently,the plant will produce fewer yields or eventually die,depending on the salinity strength.This discovery suggests that there is a definite saline threshold for the Bermuda Yellow Onion.IntroductionOriginally,Bermuda grew and exported tobacco,but during the 1870s and 1880s Bermudians approached the production of crops with a more serious attitude,and agriculture became a thriving export business.Every onion was hand picked,wrapped and packed for the market in New York.Every member of the family was involved in preparing the garden produce for export for the steamers that sailed twice a month from Hamilton.Bermuda did not only export onions to the New York market but also other garden produce such as arrowroot,celery,tomatoes,and potatoes.Because Bermudas onions were so delicious they were widely sought and enjoyed not only in the U.S.but all over,so production increased to meet the growing demand.Bermuda was often referred to as The Onion Patch and Bermudians were obviously nicknamed Onions because of this.The export of Bermuda onions came to an abrupt end when U.S.tariff walls were raised against such imports.Bermuda is quite a small island,only 21 square miles,and the crops are often exposed to salt spray from the surrounding ocean,which affects the soil that will in the long run affect plant growth.Soil is a multicomponent system,which means that soil is made up of solid,liquid and gaseous components.This system consists of inorganic and organic solid components,soil solutions and as well as a gaseous phase.These three states are in a constant flux,maintaining a state of equilibrium.This is maintained by a chain reaction,one phase will manipulate the following phases until the equilibrium state is achieved.One way of achieving equilibrium is cation exchange;this involves cations interchanging between the solid phase and the liquid phase.This exchange reaction occurs from the negative charge of soil colloids.Soil contains a mixture of different types of clays;soil salinity causes particles to bind together into aggregates,this process is called flocculation.Flocculation is good for soil aeration,root penetration,and root growth.Increasing soil salinity may have a positive effect on soil aggregation and stabilization,but high salinity also has a negative effect on plants.High sodium concentration in soil,gives an opposite affect than soil salinity.Sodium causes soil dispersion and the clay platelets and aggregate swelling.When too many sodium ions come between the clay particles,the bonded clay particles are disrupted.This separation of clay particles causes them to swell and soil dispersion occurs.Soil dispersion causes clay particles to clog soil pores;this reduces the permeability of the soil.When soil is wetted and dispersion occurs repeatedly,it then becomes solidified to a cement-like soil with little or no structure.The reason why other salts such as calcium and magnesium do not have the same affect as sodium is because they are smaller so they can collect closer to the clay particles.As shown in figure 1.Soil dispersion also has an affect on infiltration and hydraulic conductivity of the soil.A Lack o