英语翻译

Onlyspecialplantscansurvivetheterribleclimateofadesert,fortheseareregionswheretherangeofthesoiltemperaturethroughouttheyearcanbeover75℃.Furthermore,duringthesummertherearefewcloudsintheskytoprotectplantsfromthesun'srays.Anotherproblemisthefactthattherearefrequentlystrongwindsthatdrivesmall,sharpsandsintotheplants,tearinganddamagingthem.Themostdifficultproblemforallformsofplantlife,however,isthefactthateachyeartheentireamountofrainfalloccursduringafewdaysorweeksinspring.

Grassesandflowersinadesertsurvivefromoneyeartothenextbyexistingthroughthelong,hot,dryseasonintheformofseeds.Theseseedsremaininactiveunlesstherightamountofrainfalls.Ifnorainfalls,orifthereisnotenoughrainfall,theywaituntilthenextyear,orevenstillthenext.Anotherfactorthathelpstheseplantstosurviveisthefactthattheirlifecyclesareshort.Bythetimethatthewaterfromthespringrainsdisappears-justafewweeksafteritfalls-suchplantsnolongerneedany.

Theperennials(多年生植物)havespecialelementswhichenablethemtosurviveasplantsforseveralyears.Thus,nearlyalldesertperennialshaveextensiverootsystemsbelowgroundandasmallshoot(枝叶)systemaboveground.Thelargerootnetworkenablestheplanttoabsorbasmuchwateraspossibleinashorttime.Thesmallshootsystem,ontheotherhand,considerablylimitswaterlossbyevaporation(蒸发).

Anothercharacteristicofmanydesertperennialsisthataftertherainyseasontheylosetheirleavesastheyprepareforthelong,dryseason,justastreesinwetterclimateslosetheirsastheyprepareforthewinter.Thisreducestheirwaterlossbyevaporationduringthedryseason.Then,inthenextrainyseason,theycomefullyaliveoncemore,andgrownewbranches,leavesandflowers,justasthegrassesandflowersinadesertdo.