简介:Elevatedatmosphericnitrogen(N)depositionhasbeendetectedinmanyregionsofChina,butitseffectsonsoilNtransformationintemperateforestecosystemsarenotwellknown.WethereforesimulatedNdepositionwithfourlevelsofNadditionrate(N0,N30,N60,andN120)for6yearsinanold-growthtemperateforestinXiaoxing’anMountainsinNortheasternChina.WemeasuredgrossNtransformationratesinthelaboratoryusing15NtracingtechnologytoexploretheeffectsofNdepositiononsoilgrossNtransformationstakingadvantageofNdepositionsoils.NosignificantdifferencesingrosssoilNtransformationrateswereobservedafter6yearsofNdepositionwithvariouslevelsofNadditionrate.ForallNdepositionsoils,thegrossNH4+immobilizationrateswereconsistentlylowerthanthegrossNmineralizationrates,leadingtonetNmineralization.Nitrate(NO3-)wasprimarilyproducedviaoxidationofNH4+(i.e.,autotrophicnitrification),whereasoxidationoforganicN(i.e.,heterotrophicnitrification)wasnegligible.Differencesbetweenthequantityofammonia-oxidizingbacteriaandammonia-oxidizingarchaeawerenotsignificantforanytreatment,whichlikelyexplainsthelackofasignificanteffectongrossnitrificationrates.GrossnitrificationratesweremuchhigherthanthetotalNO3-consumptionrates,resultinginabuild-upofNO3-,whichhighlightsthehighriskofNlossesviaNO3-leachingorgaseousNemissionsfromsoils.ThisresponseisoppositethatoftypicalN-limitedtemperateforestssufferingfromNdeposition,suggestingthattheinvestigatedold-growthtemperateforestecosystemislikelytoapproachNsaturation.
简介:温室条件下,向盆栽山毛榉幼苗中施加192g.m·^-2^15N示踪物,研究连续两个生长季沉积氮在森林土壤(含森林地被物)、沥出物、以及地上和地下部分生物量的分配。模拟了四种处理(栽培和非栽培)下的NH4^+和NO3^-沉积情况,每种处理各自标记为^15N-NH4^+或者^15N-NO3^-。在整个体系中施加15N的总回收率分别是,盆栽处理的^15N-NH4^+为67.3%~74.9%,非盆栽处理的^15N-NO3^-为85.3%~88.1%。两种^15N示踪物主要沉积在森林土壤(包括森林地被物)中,其中盆栽处理的森里土壤中^15N-NH4^+为34.6%~33.7%,^15N-NO3^-为13.1%~9.0%,说明异养微生物有很强的固氮作用。森林土壤微生物对^15N-NH4^+的固定能力比^15N-NO3^-的固定能力强三倍。^15N-NH4^+的优先异养利用造成土壤中^15N-NH4^+的沉积量是植物体保存量的两倍而土壤中^15N-NO3^-的沉积量却低于植物体的。总之,植被-土壤系统中15N-NH4+的沉积量比^15N-NO3^-的沉积高了60%,说明了沉积氮的形式在森林生态系统中氮保存中的重要性。
简介:在湛江市坡头南三林场沿海困难立地开展了9个耐旱树种的造林试验,从树高、胸径、冠幅和保存率4个方面进行评价和选择,高生长、胸径生长和冠幅生长较快的均是大叶相思(Acaciaauriculaeformis),高生长量比平均值高1.44m;胸径生长量比平均值高出1.57cm;树冠生长量比平均值高出0.54m;9个树种保存率最高的大叶相思达91.2%,而其中3个树种大叶紫檀(Dalbergialouvelii)(47.6%)、加勒比松(PinuscaribaeaMorelet)(13.7%)、黑金刚(Ficuselastica)(9.2%)都低于50%。