<正>根据连续 8a毛白杨幼林灌溉的技术资料 ,系统地分析了灌溉效应及其特点。结果表明 :灌溉可使毛白杨叶片叶绿素和营养元素含量及其光合作用潜能提高 ,并可维持较高的生长活力、激发休眠芽萌发、促进叶片生长、加快树体增粗和枝条延长 ;灌溉对林木生长的促进作用有多面性、相异性、可变性和后效性 ;灌溉效应可分为生理效应、生长效应、再生长效应和后期效应 ,光合叶面积的复式增长为其作用核心 ;灌溉期间随土壤水分阈值提高灌溉效应增加 ,而停止灌溉后以阈值中等水平的处理后期效应最好。在干旱的 4～ 6月灌溉可使光合叶面积增加 3～ 4倍以上 ,可使胸径和树高净生长量分别提高 30 %和 40 %以上 ;停止灌溉后的 4a内 ,阈值为 50 %试验处理的材积生长量平均较对照增加了 39 67%。

Accordingtotheanalysisof8 yearsuccessivedataofirrigationonPopulustomentosaplantation ,itsef fectandcharacterwerestudiedsystematiclly.Theresultsshowthattheleaf’scontentsofchlorophyllandnutrition elementsandthepotentialofphotosynthesiswereincreasedsignificantlybyirrigating,andthetreemaintainedthe highervitalityforgrowth ,whiletheystimulatedthedormancybuds,expandedtheareaofleaf,andincreasedthethick ofthetreetruckandthelengthofitsbranchesaswell.Thecomprehensiveness,differentials ,changeableandcontinu alreactioninlaterstagewerethecharactersoftreesresponsetoirrigation.theeffectsoftreeforirrigationincluded physiologicalreaction ,growth ,reproductionandlaterstagereproduction ,andthekeyforitwastheincreasedfoliage continually .Duringtheirrigationgperiod ,theeffectofirrigationincreasedasthesoilmoistureirrigationthreshold wasraised .Butwithoutirrigationoflateryears,themiddlesoilmoisturethresholdtreatmentwasthebesttotree growth .Duringthedryseason(ApriltoJune) ,theirrigationcouldincreasethetotalfoliageareamorethan 3to 4 times,andthenetgrowthofD .B .H .andheightoftreemorethan 30 %and40 %respectively.Inthelater4-years withoutirrigation ,thevolumeofthetreewasraisedby 39.67%inaverage ,thatirrigatedwith 50 %offieldcapacity asthesoilmoisturethresholdinearly 4 -years.