野外模拟酸雨胁迫下接种外生菌根真菌对马尾松幼苗的缓解作用

外生菌根真菌能够提高宿主植物对外界环境胁迫的抵抗力。主要探讨野外条件下外生菌根真菌对酸雨胁迫下马尾松(Pinus massoniana)幼苗生长、养分元素以及表层土壤的影响,以期为酸雨严重区马尾松林恢复提供科学依据。以2年生马尾松幼苗为材料,采用原位试验,共设置6个处理:p H5.6(对照)处理未接种、对照处理接种、p H4.5酸雨处理未接种、p H4.5酸雨处理接种、p H3.5酸雨处理未接种、p H3.5酸雨处理接种。研究表明:(1)酸雨处理与对照处理相比显著降低了非菌根苗总生物量及各部位生物量(根、茎、叶),对株高无显著影响,接种外生菌根真菌可以缓解酸雨对马尾松幼苗生长的不利影响;(2)与对照处理相比,酸雨处理的非菌根苗的针叶中N、P、Ca含量升高,Mg含量降低,根系中N、P、Ca含量降低,Mg含量随p H的降低先升高后降低。接种外生菌根真菌显著提高了p H3.5酸雨处理的马尾松幼苗根系中N、P、Ca、Mg含量,而对针叶中N、P、Ca、Mg含量无显著影响。(3)在非菌根土壤中,p H3.5酸雨处理与对照处理相比显著降低了土壤中有机质、速效磷、速效钾、可溶性碳、可溶性氮、铵态氮、硝态氮含量,而接种外生菌根真菌显著提高了上述指标。酸雨对土壤阳离子交换量无显著影响。总而言之,接种外生菌根真菌促进了酸雨处理的马尾松幼苗生长、缓解了酸雨对马尾松幼苗养分元素和表层土壤的不利影响,由此可见接种外生菌根真菌是减轻酸雨对马尾松危害的一个重要途径。     

接种彩色豆马勃对模拟酸沉降下马尾松幼苗生物量的影响

外生菌根能够提高宿主植物对外界环境胁迫的抵抗力,促进植物的生长,本文试图揭示外生菌根对酸雨胁迫下马尾松生长的保护作用。本研究采用盆栽试验,共设置四个处理：酸雨对照处理（Control check (CK), 约pH值5.5）不接种,酸雨对照处理接种,酸雨pH值3.5处理不接种,酸雨pH值3.5处理接种。pH值3.5的酸雨处理降低马尾松的生物量,在试验前期降低根冠比,试验中后期则提高根冠比,在试验初期增加了叶面积,但中后期显著降低了叶面积。接种外生菌根菌有利于马尾松幼苗的生长,pH值3.5处理下接种外生菌根菌能提高马尾松幼苗的生物量,外生菌根菌对生物量分配和叶面积的影响与酸雨胁迫的影响是相反的,即外生菌根菌抵消了酸雨胁迫对马尾松的影响。     

黄山地区松树林外生菌根菌资源及生态分布

1998～2003年,对黄山地区松树林下外生菌根菌资源及生态分布进行了调查,鉴定出外生菌根菌43种,隶属于10科17属.其中马尾松林下有43种、黄山松林下有12种.马尾松幼林下的外生菌根菌种类单一,彩色豆马勃、硬皮马勃类为优势菌种;马尾松成熟林下外生菌根菌种类丰富,其优势种类为红菇科、鹅膏菌科、牛肝菌科和鸡油菌科的一些种类.并分析了树种植被对外生菌根菌分布的影响,菌根真菌的分布与温度、湿度及土壤条件的关系.     

马尾松菌根化苗木对干旱的生理响应及抗旱性评价

采用温室盆栽方法,研究了持续干旱及复水处理后,接种褐环乳牛肝菌7、牛肝菌1、鸡油菌、彩色豆马勃和土生空团菌的马尾松苗木生理变化,并对菌根化苗木进行抗旱性评价.结果表明:在持续干旱条件下,马尾松苗木的丙二醛和相对质膜透性随之增加,但菌根化苗木的丙二醛和相对质膜透性均显著低于未接种苗木(对照);复水后,菌根化苗木中丙二醛和质膜透性较对照迅速降低.在持续干旱胁迫前21 d,马尾松苗木超氧阴离子自由基产生速率增加,同时也诱导了菌根化苗木中过氧化物歧化酶、过氧化物酶和硝酸还原酶活性显著增加.随着胁迫时间的延长,苗木复水后的恢复能力各异.在胁迫14 d复水后,苗木过氧化物歧化酶、过氧化物酶和硝酸还原酶的活性均得以恢复.菌根化苗木抗旱性的强弱为牛肝菌7＞牛肝菌1＞鸡油菌＞土生空团菌＞彩色豆马勃.过氧化物歧化酶和丙二醛与马尾松菌根化苗木抗旱性关联度较大,可以作为抗旱鉴定的主要指标.     

外生菌根菌不同接种方法对樟子松苗木生长的影响

 以提高外生菌根真菌对樟子松(Pinus sylvestris var. mongolica)苗木促生长效果为目的, 在前期研究的基础上, 采用菌株配对培养的方法对获得的樟子松外生菌根真菌进行混合接种菌株组合筛选; 采用苗木截根-菌液浸根和沟施接种方法分别对2年生和3年生樟子松苗木进行野外单接种及混合接种。研究外生菌根真菌不同接种方法、菌株单接种及混合接种对樟子松苗木生长的影响。试验结果表明: 供试菌株及菌株组合对樟子松苗木生长均有一定的促进作用。菌株GT005和菌株035为供试菌株中对樟子松苗木促生长效果最佳的菌株。采用苗木截根-菌液浸根方法接种2年生樟子松苗木130 d, GT005接种的苗木高生长提高54%, 地径生长提高15%, 过氧化氢酶活性提高48%, 而根系活力降低3%; 菌株035接种的苗木高生长提高42%, 地径生长提高56%, 过氧化氢酶活性提高47%, 根系活力提高11%。沟施接种方法接种3年生樟子松苗木100 d, GT005接种苗木高生长提高10%, 地径生长提高15%, 过氧化氢酶活性提高90%, 而根系活力降低34%; 菌株035接种苗木高生长提高7%, 地径生长提高9%, 过氧化氢酶活性提高6%, 而根系活力降低46%; 菌株组合044/GT001和GT001/GT005 接种的苗木高生长仅比对照提高3.47%和2.07%, 而菌株组合 044/025 和044/009 接种的苗木高生长低于对照; 混合接种的苗木其地径生长高于对照0.16%～7.98%。综上所述, 苗木截根-菌液浸根接种方法对苗木的促生长效果显著高于沟施接种方法; 外生菌根菌高效菌株与一般菌株混合接种会弱化高效菌株自身接种效果; 苗木过氧化氢酶活性、苗木根系活力与苗木的生物量间无相关性。     

红皮云杉外生菌根菌单接种及混合接种对苗木生长的影响

以提高外生菌根真菌对红皮云杉苗木促生长效果为目的,在前期研究的基础上,采用菌株配对培养的方法对获得的云杉外生菌根真菌进行混合接种菌株组合筛选;采用沟施菌剂方法,对3年生红皮云杉移床苗进行外生菌根菌菌株组合野外混合接种试验,同时以各菌株野外单接种作为对照,研究外生菌根真菌单接种及混合接种对红皮云杉苗木生长的影响。试验结果表明:供试菌株及菌株组合对红皮云杉苗木生长均有一定的促进作用。菌株L15促生长效果最佳,接种100d苗木高生长高于对照30.88%,地径高于对照15.29%。组合L15/025与L15/009促苗木生长效果低于单接种L15的效果,高于单接种009和025的效果。接种菌株010和组合L15/025的苗木与对照相比,叶绿素含量提高差异显著,叶绿素a水平分别高于对照59.15%、54.61%,叶绿素b水平分别高于对照76.34%和67.78%。除接种菌株010的苗木外,其他处理苗木其过氧化氢酶活性与对照相比均有所降低。所有处理苗木的根系活力均低于对照。综上,外生菌根菌高效菌株与一般菌株混合接种会弱化高效菌株自身接种效果;苗木过氧化氢酶活性、苗木根系活力与苗木的生物量间无相关性。     

外生菌根真菌菌丝对马尾松苗氮素传递的影响

为探究外生菌根真菌菌丝对马尾松Pinus massoniana幼苗氮素的吸收、传递及分配规律的影响,本研究应用¹⁵N示踪技术,采用四室隔网系统进行盆栽试验。研究表明：供体接种外生菌根真菌后,根外菌丝能够穿过粘土层和隔离层到达受体室,在供、受体植株之间形成菌丝桥。接种不同外生菌根真菌均显著增加供体植株苗高、地径及生物量(P<0.05),但对受体植株的影响有差异,其中接种橙黄硬皮马勃Scleroderma citrinum (Sc)对植株苗高、地径及生物量具有显著的促进作用(P<0.05)。接种对供、受体植株全氮含量无显著性的规律(P>0.05),只有接种东方豆马勃Pisolithus orientalis (Po)的植株全氮含量显著高于其他处理。接种能够显著提高供体植株根、茎、叶的吸氮量,且叶>根>茎,受体植株中,接种Po、Sc和褐环乳牛肝菌Suillus luteus (Sl)的植株总吸氮量较不接种(NE)显著增加(P<0.05),而接种混合菌(Sm)的植株与NE无显著差异(P>0.05)。接种Sl的植株¹⁵N传递率最高(75.86%),受体植株对¹⁵N吸收量最大(91.68 μg/pot),Po次之。供体植株中,除接种Sl的植株¹⁵N主要分配在叶外,其他处理的¹⁵N分配中心均在根部,在受体植株中,接种Po、Sl、Sm的植株¹⁵N主要分配在根部,而NE和接种Sc的植株¹⁵N主要分配在茎。综上,在马尾松供、受体苗木间能形成菌丝桥,接种外生菌根真菌能够促进马尾松供体植株苗高、地径的生长及生物量的积累,提高植株吸氮量,对于受体植株不同菌种的作用有差异,其中接种Sc的苗木表现最好。此外,不同的菌种菌丝对植株的全氮含量、¹⁵N吸收量、传递率及分配率的影响也不同,其中,以接种Po和Sl的苗木表现较好。     

菌根化马尾松对干旱胁迫的响应及其内源多胺的变化

以分别接种4种外生菌根真菌及其混合菌的5种菌根化马尾松植株为材料,在室内进行自然模拟干旱胁迫处理,考察了各处理植株的萎蔫率、萎蔫度及其针叶中的腐胺(Put)、亚精胺(Spd)和精胺(Spm)含量的变化,探讨多胺在外生菌根提高马尾松抗旱能力过程中的作用.结果显示:接种外生菌根真菌能够显著提高植株定植土壤的保水能力,显著降低植株的萎蔫率和萎蔫度;在干旱胁迫过程中,菌根化植株的Spm含量、多胺总量均高于对照植株且含量相对稳定,而菌根化植株和对照植株的Spd含量均无明显变化, 对照植株和紫金蜡蘑菌根化植株的Put含量相对较高且变化幅度较大.研究发现,外生菌根能提高马尾松植株内源Spm含量和Put的降解能力,调节各种内源多胺的分配比例,最终显著提高马尾松植株的抗旱能力.     

丛枝菌根（AM）真菌对翅果油树幼苗根系的影响

采用接种和不接种(对照)丛枝菌根的方法对翅果油树幼苗在不同生长时期的形态、生物量、矿质元素含量及抗逆性等指标进行比较分析,以探讨丛枝菌根(AM)改善翅果油树在生态系统中的退化及濒危现状的机理.结果显示:(1)摩西球囊霉(Glomus mosseae)和脆无梗囊霉(Acaulospora delicata)与盆栽翅果油树苗木可形成菌根;菌根化苗木的形态及生物量等指标均与对照差异极显著,且与菌根侵染率呈显著正相关(P<0.05).(2)菌根使苗木根系体积增大、总吸收面积增加、根系的活跃吸收面积显著增加,且根系中活跃吸收面积比与磷、钾元素含量呈显著正相关(P<0.05).(3)苗木生长的盛期和末期,菌根化苗木根系过氧化物酶活性显著高于对照,而在生长后期却显著低于对照呈负相关(P<0.05);菌根化苗木根系多酚氧化酶活性显著高于对照(P<0.05),在苗木生长盛期酶活性最强,但接种不同菌种的苗木间差异不显著.研究表明,与不接种相比,接种菌根增加了翅果油树的根系吸收能力,提高了根系酶体系,有利于植物抵抗各种胁迫,对扩大翅果油树植物的分布区有重要意义.     

黔中地区火灾对马尾松外生菌根真菌群落的影响

林火会对森林植被及其相关联的微生物群落产生重要影响。为揭示火灾对马尾松外生菌根真菌(ectomycorrhizal fungi,EMF)群落的影响,本研究以火灾马尾松林为研究对象,以周边立地条件相对一致、未火灾马尾松林为对照,采用形态鉴定与分子生物学技术相结合的研究方法,分析火灾对马尾松EMF群落的影响。共鉴定出马尾松EMF OTUs 69个,隶属于2门7纲15目18科23属,且担子菌门丰富度明显高于子囊菌门。火灾显著改变了马尾松EMF群落的组成和结构,其中火灾马尾松林中EMF群落的优势属主要为蜡蘑属Laccaria、红菇属Russula和棉革菌属Tomentella,未火灾马尾松林中EMF群落的优势属主要为乳菇属Lactarius、棉革菌属Tomentella和土生空团菌属Cenococcum。火灾样地马尾松的EMF群落相对于对照样地在组成与结构上存在明显差异,表现出特有OTUs高于共有OTUs。相对于未火灾马尾松林,火灾马尾松EMF群落的多样性指数和丰富度指数呈下降趋势(P>0.05)。RDA分析表明,pH和TP是影响马尾松EMF群落的重要环境因子。综上所述,火灾干扰是影响黔中地区马尾松EMF群落的重要生态因素之一。     

不同林相的松针对马尾松毛虫生长发育的影响

为探讨混交林中松树对害虫的生态调控作用机制,研究了不同林分类型下马尾松林和湿地松林对马尾松毛虫生长发育的影响。结果表明,取食马尾松针叶的马尾松毛虫与取食湿地松针叶的相比,其发育历期缩短,死亡率降低,幼虫及蛹（雌、雄）重增加,化蛹率、羽化率和产卵量均提高;且其幼虫的代谢量（取食量与排泄量）更大,对食物的利用与消耗的各项指标均高。取食不同林分类型下的同一种松树（马尾松或湿地松）针叶的马尾松毛虫,以取食纯林松针的幼虫生长发育更快,死亡率更低,化蛹率、羽化率和产卵量更高,对食物的利用、转化和消耗率更强。混交林中的松针不利于马尾松毛虫的生长发育和种群增长。     

退化红壤植被恢复后土壤轻组有机质的季节动态

以次生林为对照,研究了福建省长汀县河田镇侵蚀退化红壤及其恢复为马尾松林、板栗园和百喜草地后土壤轻组有机质的季节变化.结果表明:侵蚀裸地表层土壤轻组有机质含量在0.05~0.14 g·kg^-1,无明显的季节变化;恢复的马尾松林、板栗园和百喜草地表层土壤轻组有机质含量季节变化明显,其中冬春季节比夏季高58%～122%.夏季恢复植被下的土壤轻组有机质C含量和C/N均较低,而轻组有机质N含量较高,表明夏季高温、高湿的气候条件导致轻组有机质快速分解.次生林轻组有机质的季节变化趋势与恢复的生态系统基本一致,但波动幅度较小,5～10 cm土层轻组有机质含量无明显的季节差异.土壤轻组有机质的季节动态还受小生境和植被类型的影响,与林地相比,百喜草地土壤轻组有机质数量波动幅度较高.建议采用多次取样或者综合气候、植被和经营措施等因素确定合适的取样时间,以提高轻组有机质的观测精度.     

北京东灵山区两种生境条件下辽东栎幼苗补充与建立的比较

 北京东灵山区的人工油松（Pinus tabulaeformis）林中常常混生有萌生的辽东栎（Quercus wutaishanica）种群。局部地带辽东栎与油松形成混交林,在山脊及山坡上部一些特殊生境辽东栎甚至取代油松林成为优势种。为了探讨北京东灵山区辽东栎林的天然更新机制及辽东栎幼苗在人工油松林中的天然更新,在油松人工林的林下和林缘两种生境条件下将辽东栎种子播种于2 cm深的土中,对辽东栎幼苗的补充和建立进行了对照试验。结果显示,在辽东栎结实丰年,两种生境条件下播种后辽东栎种子丢失差异并不显著,而辽东栎幼苗补充和建立方面的差异极显著。由于森林动物特别是啮齿类动物的活动对辽东栎幼苗建立的影响具有二重性：消耗种子与促进萌发,本试验特别关注辽东栎幼苗子叶丢失现象及其丢失后果。由于辽东栎种子萌根较早,在幼苗出土前其粗大的主根长达10～20 cm,并已初步形成根系,表明已有相当比例的营养物质从子叶转移到根部。因此当幼苗出土后如果仅仅只是子叶的丢失对辽东栎幼苗的成活和生长均无明显的影响。通过研究发现辽东栎幼苗期子叶丢失有3种形式：1）仅丢失子叶,幼苗其它部位未受伤害,多发生在林缘生境中,占发芽坚果的29.69%;2）整个幼苗连根被拖出地面,多发生在林下生境,占62.43%;3）在子叶与根颈的连接处主干被咬断,林缘为50.88%,显著高于林下的8.41%。但只有后两种形式才导致幼苗死亡。导致这些现象的原因是由于林缘土壤腐殖质含量低,比较干燥,土质较坚实,以及幼苗出土前坚果主根生长得较长等缘故,当幼苗遭受动物捕食时不会轻易地被拖出地面,拖走的往往仅仅是子叶。至生长季节结束,林缘样方辽东栎幼苗的成活率接近20%,茎干平均高度7.94 cm,芽数11.24·株-1,叶片平均干重为81.14 mg·株-1,且几乎全部由丢失子叶的幼苗所构成;而林下样方辽东栎幼苗的成活率不足2%,茎干平均高度4.74 cm,芽数7.52·株-1,叶片平均干重仅为42.27 mg·株-1,以未丢失子叶的幼苗为主。试验结果表明,林缘及类似林缘的环境条件更有利于辽东栎的实生更新。     

七株外生菌根真菌与三种松苗菌根的形成能力

松树外生菌根菌资源丰富,但实际应用的种类不多。为筛选出与松苗形成菌根能力较强的菌种,采用播种接菌和芽苗截根移栽接菌两种方法,对7株外生菌根真菌与马尾松、湿地松和黑松3种松苗的菌根合成进行了研究。结果表明：形成的菌根以二叉分枝状为主,棒状菌根相对较少,多叉状菌根以马尾松较多。PC2形成的菌根表面菌丝厚且紧密,504、EG、Pt,形成的菌根表面菌丝紧密程度中等,而505、ZJ和HX形成的菌根其表面菌丝则比较稀疏;Pt1、Pt2、EG形成的菌根外延菌丝较长,而505、HX形成的菌根外延菌丝极短。截根接菌时的感染率和感染指数要高于播种接菌。504形成菌根的能力最强,在3种松苗上的菌根感染率都达100％,感染指数最高可达90,最低也达70;Pt2和EG与马尾松和黑松形成菌根的能力较强;而505和HX仅与马尾松形成菌根的能力较强;Pt1形成菌根的能力较差,在3种松苗上菌根感染率和感染指数都较低。在3种松苗中,马尾松的菌根化状况最好,其次为黑松,湿地松的菌根化状况较差。     

中国东部主要松林营养元素循环的比较研究

 中国的松林主要分布在亚热带和温带地区,在亚热带和温带地区东部主要是马尾松林、华山松林、油松林、红松林和樟子松林。松林由于树种、起源和年龄的差别,其生物量的变化幅度较大,在65～200t·hm-2之间(东北地区的原始红松林最高生物量可达360t·hm-2),松林的生物量表现出区域分异的特点。即从南到北随着纬度的增加,林分的生物量有逐渐降低的趋势。松树针叶中5种主要营养元素含量表现为[N]>[K]≥[Ca]>[Mg]≥[P],而且营养元素表现出因种而异,N的含量为华山松≥马尾松>油松≥红松>樟子松,而P和K在油松和红松针叶中含量较高;Ca的含量表现出较大的波动,与其母岩关系密切。松林主要营养元素(N、P、K、Ca、Mg)的积累量中N一般占25％～40％,松林营养元素循环速率受生境,树种、年龄的影响,但总的来说,亚热带地区松林营养元素的循环速率高于温带地区松林。     

The productivity of pine plantations in relation to previous land use

Summary Differences in the productivity of establishedP. radiata plantations on pasture and forest soils were found to be reproducible withP. radiata seedlings in a glasshouse environment. The growth of seedlings on pasture soil exceeded that of seedlings on native forest soil (the ‘primary pasture effect’). After a history of pine on both native and pasture soils a residual effect of pasture on seedling growth was evident (the ‘secondary pasture effect’). However, the effect of a history of pine plantation (the ‘pine effect’) was to decrease the productivity of both native and pasture soil as assessed by seedling growth. These effects were not related to changes due to land management in mycorrhizal infection or in soil structure. The analysis of seedling growth leads to the conclusion that soil fertility, particularly the availability of nitrogen and phosphorus, has changed.     

Natural regeneration of Pinus resinosa on burned and unburned sites in Newfoundland

Abstract. Natural regeneration of Pinus resinosa (red pine) seedlings around mature trees was studied in burned and unburned stands. Growth inhibitory effects of the forest organic matter on red pine seedlings was tested by a stair-step experiment using leachate of forest soil monoliths and also by a seed germination bio-assay using forest floor substrates. To test if higher burning temperatures can remove the allelopathic effects of red pine-Kalmia organic matter, a laboratory bio-assay was conducted by germinating red pine seeds on the organic matter burned at 200, 400, 600 and 800°C. Deposition of dry needles and a thick duff layer under red pine stands affected seedling establishment. Red pine seedling establishment increased with the decreasing thickness of duff layer away from the stump of the seed-bearing trees. Wildfire helped in removing the duff layer and increased seedling establishment. A high fuel load within a 0 - 1 m radius around the tree stump caused a deep burn of the organic matter including part of the soil seed reserve. On a burned-over surface, more seedlings established in a band between 1 and 2 m around the stump than inside and outside the band. Primary root growth of red pine was severely inhibited when the seedlings were grown in unburned forest floor organic matter where Kalmia was the principal understory species. Water leachate of a Pinus resinosa-Kalmia soil monolith was inhibitory to red pine seedling growth. In greenhouse conditions, the seedlings grew well in burned-over soil from a Pinus resinosa stand. Burned organic matter from a red pine forest showed an increase in pH with a burning temperature of 600°C. Primary root growth of red pine seedlings was similarly increased with increasing temperature up to 600°C; at higher temperatures the root length of seedlings did not increase any further.     

Short-Term Medieval Settlement Activities Irreversibly Changed Forest Soils and Vegetation in Central Europe

In Europe, many contemporary forests are not continuous, but were established on former agricultural land in territories of deserted villages. We aimed to explore whether medieval settlement activities of only 60 years irreversibly changed soil properties and whether these changes were reflected by contemporary forest vegetation. The research was performed in the deserted village of K?í, which existed from 1357 to ca 1420 AD in a current oak forest on sandy soils in the Czech Republic. We identified four former land-use types (building sites, courtyards, the village square, and gardens), where we analyzed soil properties and plant species composition of the forest understory. Higher concentrations of plant-available P, K, Ca, and Mg as well as the total concentrations of organic C and trace elements (As, Cd, Cu, and Zn) were recorded at former building sites with neutral soils, compared to the other former land-use types with acidic soils. The four-times higher species richness at former building sites compared to the former gardens indicate the strong effect of soil pH and nutrient availability on plant species composition, even on the spatial scale of several square metres. Understanding recent patterns in soil properties and biodiversity in Central European forests requires detailed knowledge of former land use over centuries. Analysis of contemporary soil properties together with analysis of vegetation can help to identify former land-use types in deserted villages.     

ROLE OF MYCORRHIZAL FUNGUS ORIGIN IN GROWTH AND NUTRIENT UPTAKE BY GERANIUM ROBERTIANUM

Prior field studies have shown that populations of forest herbs on relatively nutrient poor soils have higher vesicular-arbuscular mycorrhizal (VAM) infection intensity than plants on rich soils. However, the growth responses and ability to take up P against the soil nutrient gradient are often not linearly related to infection intensity. To determine if intraspecific differences among populations of the common VAM fungus Glomus occultum could differentially affect growth and nutrient uptake, Geranium robertianum seedlings were inoculated with Glomus occultum isolated from four forest types along a gradient of soil fertility, and grown in a greenhouse at P levels typical of the extremes of that gradient. Plants given inoculum from relatively infertile forest sites generally produced greater root, shoot, and total mass than plants given inoculum from fertile sites or uninoculated plants, especially at the low P supply rate. Total P uptake and both P and N uptake efficiency were also highest in plants given inocula from low fertility sites. These results indicate that local adaptation and intraspecific variations in the ability of VAM fungi to induce growth and nutrient uptake effects on host plants may be as important as interspecific differences among VAM fungus species.     

Maintenance and Impacts of an Inoculated mer/luc-Tagged Pseudomonas fluorescens on Microbial Communities in Birch Rhizospheres Developed on Humus and Peat

Antagonistic bacteria represent promising biocontrol agents for improving forest production in seedling nurseries or forest soils. The fate of an introduced mer/luc-tagged antagonistic Pseudomonas fluorescens 31K3 was monitored in the rhizosphere of silver birch (Betula pendula) seedlings grown in microcosms containing forest humus or nursery peat. The inoculated strain (10(8) cfu g(-1) soil) was unable to establish in significant numbers in either soil type and turned nonculturable in humus. Detection in both soils was possible only via luminescence of enrichment cultures 80 days post-inoculation. Despite low P. fluorescens survival, inoculation had a positive effect on seedling growth. Limited impact of inoculation on the indigenous microbial communities was identified following analyses of respiration and denitrification potential, community-level physiological profiles and molecular fingerprinting of fungi and eubacteria, and Pseudomonas community structures. The minor changes observed in the indigenous microbial communities, including mycorrhiza development, were not consistent between humus and peat growth substrates. It was concluded that the rhizosphere-related microbial communities developed in both of these highly organic soil systems are highly buffered against introduction of foreign bacteria.