TPO-5 Reading 1 阅读译文

MINERALSAND PLANTS矿物质和植物Research hasshown that certain mineralsare requiredby plantsfor normalgrowthand development.The soilis thesource of these minerals,which areabsorbed bythe plantwiththe waterfrom thesoil.Even nitrogen,which is a gasin itselemental state,is normallyabsorbedfrom thesoil asnitrate ions.Some soilsare notoriouslydeficient inmicronutrients andare thereforeunable tosupport mostplant life.So-called serpentinesoils,forexample,are deficientin calcium,and onlyplants ableto toleratelow levels of thismineralcan survive.In modernagriculture,mineral depletionof soilsisamajor concern,sinceharvesting cropsinterrupts therecycling ofnutrients backto thesoil.研究表明，某些矿物质是植物正常生长发育所必需的土壤是这些矿物质的来源，它们通过水分被植物从土壤中吸收即使是元素状态为气体的氮，也通常作为硝酸根离子从土壤中被吸收众所周知，一些土壤缺乏微量营养素，因此大多数植物不能生长例如所谓的蛇纹岩土壤，由于缺乏钙，只有那些能忍受如此低含量的钙的植物才能够存活在现代农业中，土壤矿物质枯竭是一个大问题，因为收割庄稼切断了养分返回土壤的循环Mineral deficiencies can oftenbe detectedby specificsymptoms such as chlorosislossof chlorophyllresulting inyellow orwhite leaftissue,necrosis isolateddeadpatches,anthocyanin formationdevelopment ofdeep redpigmentation ofleaves orstem,stunted growth,and developmentof woodytissue inan herbaceousplant.Soils aremostcommonly deficientin nitrogenand phosphorus.Nitrogen-deficient plantsexhibit manyofthe symptomsjust described.Leaves developchlorosis;stems areshort andslender,andanthocyanin discolorationoccurs onstems,petioles,and lowerleaf surfaces.Phosphorus-deficient plantsare oftenstunted,with leavesturning acharacteristic darkgreen,often withthe accumulationof anthocyanin.Typically,older leavesare affectedfirstas thephosphorus ismobilized toyoung growingtissue.Iron deficiencyis characterizedbychlorosis betweenveins inyoung leaves.矿物质缺乏通常可由特定的症状检测出来，如褪绿叶绿素损失导致黄叶或白叶的现象、坏疽孤立的坏死斑、花青素的形成形成深红色叶片和茎色素沉积、发育不良以及草本植物长木质组织土壤最常缺乏的是氮和磷氮缺乏植物表现出了刚才描述的许多症状叶片黄化、茎短而细以及发生在茎、叶柄以及下叶表面的花青素变色磷缺乏的植物往往发育不良，叶片变成特殊的深绿色，经常伴随着花青素的积累由于磷流向新生的组织，通常较老的叶片首先受到影响铁缺乏症的特点是嫩叶的叶脉之间萎黄Much of the researchon nutrientdeficiencies isbased ongrowing plantshydroponically,that is,in soillessliquid nutrient solutions.This techniqueallowsresearchers tocreate solutionsthat selectivelyomit certainnutrients and then observetheresulting effectson the plants.Hydroponics hasapplications beyondbasic research,since itfacilitatesthe growingof greenhousevegetables duringwinter.Acroponics,a techniqueinwhich plantsare suspendedandtheroots mistedwith anutrientsolution,is anothermethodfor growingplants withoutsoil.大多数关于营养素缺乏症的研究都基于水培法，即在无土营养液中培养这项技术允许研究人员创造缺乏某种营养素的溶液，然后观察对植物生长造成的影响水培法的应用已经超越了基础研究，因为它促进了温室蔬菜在冬季的生长空气培养法，一种把植物悬挂起来，将其根部喷上营养液的技术，是另外一种无土栽培的方法While mineraldeficienciescanlimit thegrowth ofplants,an overabundanceof certainmineralscan betoxic andcan alsolimit growth.Saline soils,which havehighconcentrations ofsodium chlorideand othersalts,limit plantgrowth,and researchcontinuesto focuson developingsalt-tolerant varietiesof agriculturalcrops.Research hasfocusedon thetoxic effectsof heavy metals suchas lead,cadmium,mercury,andaluminum;however,even copperand zinc,which areessential elements,can becometoxicin highconcentrations.Although mostplants cannotsurvive inthese soils,certain plantshavethe abilityto toleratehigh levels of theseminerals.虽然缺乏矿物质会抑制植物生长，但某些矿物质过量可能会有毒，同样也会抑制植物生长含有高浓度的氯化钠和其他盐类的盐碱土壤抑制植物生长，于是研究继续集中开发耐盐农作物品种着重研究重金属的毒性作用，如铅、镉、汞、铝；然而即使是铜和锌这样的必需元素，如果浓度过高也会产生毒性虽然大多数植物无法在这种土壤生存，某些植物却能够忍耐如此高含量的矿物质Scientists haveknown forsome timethatcertainplants,called hyper accumulators,can concentrateminerals atlevels ahundredfold orgreater thannormal.■A surveyofknown hyperaccumulators identifiedthat75percent of them amassednickel,cobalt,copper,zinc,manganese,lead,and cadmiumare otherminerals ofchoice.aHyperaccumulators runthe entirerange ofthe plantworld.■They maybe herbs,shrubs,or trees,■Many membersofthemustard family,spurge family,legume family,and grassfamilyare tophyperaccumulators.Many arefound intropical andsubtropical areasoftheworld,where accumulationof highconcentrations ofmetals mayafford someprotection againstplant-eating insectsand microbialpathogens.科学家早前就了解到，某些所谓的富集植物能够比普通植物多集中100倍甚至更多的矿物质一项对已知富集植物的调查表明，它们中75%积聚了锦而钻、铜、锌、镒、铅和镉则是其他选择性聚集的矿物质富集植物存在于整个世界范围，它们可能是草本植物、灌木或树芥属、大戟属、豆科和禾本科植物中的许多成员都是靠前的富集植物许多富集植物被发现于热带和亚热带，金属可以为植物提供保护，对抗植食昆虫和细菌病原体Only recentlyhave investigatorsconsidered usingthese plantsto cleanup soilandwaste sitesthat havebeen contaminated by toxiclevelsofheavymetals-anenvironmentally friendlyapproach knownas phytoremediation.This scenariobegins withtheplanting ofhypei accumulatingspecies inthe targeta】ea,suchasan abandonedmine oranirrigation pondcontaminatedbynmoff.Toxic mineralswould firstbe absorbedby rootsbutlater relocatedto thestem andleaves.A harvestoftheshoots wouldremove thetoxiccompounds offsite tobe burnedor compostedto recoverthe metalfor industrialuses.Afterseveral yearsof cultivationand harvest,the sitewould berestored ata costmuch lowerthanthe priceof excavationand reburial,the standardpractice forremediation ofcontaminatedsoils.For examples,in fieldtrials,theplantalpine pennycressremoved zincand cadmiumfromsoils neara zincsmelter,and Indianmustard,native toPakistan andIndia,has beeneffectivein reducinglevelsofselenium saltsby50percent incontaminated soils.直到最近研究者才考虑用这些植物来清理已经被有毒重金属污染的土壤和废弃物物处理点——一种被称为植物修复法的修复方法这套方案首先从在目标区域种植超积累物种开始，如在废弃矿井和被径流污染的灌溉池塘有毒矿物质首先被根吸收，随后被运送至茎和叶收割下来的枝叶将被焚烧以移除有毒化合物或被制成混合肥料回收金属用于工业经过几年的种植和收割，该污染点将被修复，而其造价远比修复污染土壤的标准做法——挖掘和填埋低得多举例来说,在实地试验中，高山薪箕从靠近一个锌冶炼厂的土壤中去除了锌和镉，原产自巴基斯坦和印度的印度芥菜可以将染土壤中硒的水平有效地降低50%o。