High diversity of arbuscular mycorrhizal fungi in a boreal herb-rich coniferous forest

* Here, the diversity of arbuscular mycorrhizal (AM) fungi was determined in a boreal herb-rich coniferous forest in relation to environmental variables. * Root samples of five plant species (Fragaria vesca, Galeobdolon luteum, Hepatica nobilis, Oxalis acetosella and Trifolium pratense) were analysed from stands differing in age and forest management intensity. * Thirty-four Glomeromycota taxa (small-subunit ribosomal RNA gene (SSU rDNA) sequence groups) were detected from 90 root samples (911 clones), including eight new taxa. Sequence groups related to Glomus intraradices were most common (MO-G3 and MO-G13). Samples of H. nobilis were colonized by more AM fungal taxa (3.68 +/- 0.31) than those of O. acetosella (2.69 +/- 0.34), but did not differ significantly in this respect from those of F. vesca (3.15 +/- 0.38). Effects of forest management, host plant species (except above) or season on the number or composition of fungal taxa in root samples were not detected, and neither were they explained by environmental variables (vegetation, soil and light conditions). * This is the most taxon-rich habitat described to date in terms of root-colonizing Glomeromycota. The data demonstrate the importance of temperate coniferous forests as habitats for AM fungi and plants. Lack of obvious fungal community patterns suggests more complex effects of biotic and abiotic factors, and possibly no adverse effect of common forest management practices on AM fungal diversity.     

环境因子对AM真菌多样性的影响

土壤,气候和地理因子等环境因子对丝枝菌根（AM）真菌多样性有重要影响,本文系统地综述了最近10年来AM真菌生态学在该方面的最新研究成果,分析当前研究中所存在的问题和动向。     

Effect of drought and season on arbuscular mycorrhizal fungi in a subtropical secondary forest

Arbuscular mycorrhizal (AM) fungi in both soil and roots were examined in May (summer) and December (winter) under a 4-y drought experiment in a Chinese subtropical secondary forest. Drought significantly decreased AM fungal extra-radical hyphal density, spore density, and root colonization rate in both seasons. These AM parameters were significantly higher in summer than in winter in the control treatment, but only AM fungal extra-radical hyphal density exhibited the same seasonal trend in the drought treatment. In total, 45 AM fungal operational taxonomic units (OTUs) were obtained at a 97% sequence similarity level using Illumina sequencing of 18S rDNA. Drought and season had no significant effects on AM fungal OTU richness in soil and roots. AM fungal community composition in soil and roots was significantly affected by season but not by drought. This finding enhances our understanding of the response of AM fungi to global climate change in subtropical forest ecosystems.     

Medicago species affect the community composition of arbuscular mycorrhizal fungi associated with roots

Sequencing of the 5' end of the large ribosomal subunit (LSU rDNA) and quantitative polymerase chain reaction (qPCR) were combined to assess the impact of four annual Medicago species (Medicago laciniata, Medicago murex, Medicago polymorpha and Medicago truncatula) on the genetic diversity of arbuscular mycorrhizal (AM) fungi, and on the relative abundance of representative AM fungal genotypes, in a silty-thin clay soil (Mas d'Imbert, France). Two hundred and forty-six Glomeromycete LSU rDNA sequences from the four plant species and the bulk soil were analysed. The high bootstrap values of the phylogenetic tree obtained allowed the delineation of 12 operational taxonomic units (OTUs), all belonging to Glomus. Specific primers targeting Glomeromycetes and major OTUs were applied to quantify their abundance by qPCR. Glomeromycetes and targeted OTUs were significantly more abundant in the root tissues than in the bulk soil, and the frequencies of three of them differed significantly in the root tissues of the different plant species. These differences indicate that, despite the absence of strict host specificity in mycorrhizal symbiosis, there was a preferential association between some AM fungal and plant genotypes.     

安徽茶区茶树丛枝菌根真菌多样性

调查了安徽茶区茶树丛枝菌根真菌(AMF)资源分布情况,为菌根生物技术在茶产业中的应用提供了具有应用价值的菌种资源.采用醋酸-墨水染色法观察茶树丛枝菌根(AM)的侵染率、侵染级数、侵染强度和菌根类型;采用湿筛法获得AMF孢子,进行形态学鉴定.结果表明: 在安徽茶区,AMF能够侵入茶树根系形成典型的共生体,侵染率在36%～95%,侵染级数均在3级以上,侵染强度大;从安徽茶树根际土中共鉴定出8属36种AMF,其中缩管柄囊霉是优势种,网状球囊霉、刺无梗囊霉、孔窝无梗囊霉、詹氏无梗囊霉、双网无梗囊霉和凹坑无梗囊霉是常见种,褐色管柄囊霉、疣突管柄囊霉、毛氏无梗囊霉、近明管柄囊霉、瑞氏无梗囊霉、空洞无梗囊霉、晕环球囊霉、细齿无梗囊霉、地管柄囊霉、幼套球囊霉、蜜色无梗囊霉、稀有内养囊霉是稀有种,其余17种为少见种;不同采样地茶树根际AMF群落相似性系数(0.14～0.55)较低,多属于低和中等水平;相关性分析表明,孢子密度与侵染率呈显著正相关,种的丰度与侵染率和总球囊霉素相关土壤蛋白呈显著正相关.安徽茶区茶树根系存在典型的AM结构,其根际AMF多样性丰富,为开发茶树专用AMF肥料提供了丰富的菌种资源.     

Effects of long-term NP-fertilization on abundance and diversity of arbuscular mycorrhizal fungi under a maize cropping system

Diversity of arbuscular mycorrhizal fungi (AMF) in 27-year long-term NP-fertilization plots under a maize cropping system in Thailand was studied through spore morphological characterization. The plots received 0–0, 60–60, 120–120 and 180–180 kg N-P₂O₅ ha^–1 year^–1 as ammonium sulfate and triple superphosphate. The plots were sampled monthly for one year, the AMF spores were counted and morphotyped, and taxa were identified after morphotyping and monospecific pot culture. Spore number g^–1 soil, relative spore abundance and Shannon-Wiener indexes were calculated. Sixteen putative taxa were recorded from the field of which nine sporulated on maize roots in pot culture. The long-term fertilization caused decreases in AMF total spore numbers and variation in species diversity depended on sampling time. Effects of fertilization on spore number and also relative spore abundance varied with species and sampling time. Among the nine species sporulating under maize, only Acaulospora sp.1 showed no change (P > 0.003 after Bonferroni correction) in spore number with fertilization in the field; and was therefore classified as an AMF species insensitive to fertilization. Spores of Entrophospora schenckii, Glomus mosseae, Glomus sp.1, Glomus geosporum-like and Scutellospora fulgida, though they decreased in absolute numbers in response to fertilization, showed no change (P > 0.003 after Bonferroni correction) in relative abundance; these species were classified as AMF species slightly sensitive to fertilization. Three unidentified species of Glomus, though they decreased in absolute numbers in response to fertilization, showed decreases (P < 0.003 after Bonferroni correction) in relative abundance; these species were classified as AMF species highly sensitive to fertilization.     

Temporal temperature gradient gel electrophoresis (TTGE) as a tool for the characterization of arbuscular mycorrhizal fungi

The aim of this study was to assess the feasibility of using temporal temperature gradient electrophoresis (TTGE) of PCR-amplified 18S rDNA fragments of different Glomus species for their detection and characterization. Screening of Glomus clarum, Glomus constrictum, Glomus coronatum, Glomus intraradices, Glomus mosseae and Glomus viscosum by PCR-TGGE revealed that the NS31-AM1 region of the 18S rRNA gene contained insufficient variation to discriminate between them. In contrast, TTGE analysis of the NS31-Glo1 region, which was obtained by nested PCR of the NS31-AM1 amplicon, showed that each species was characterized by a specific TTGE fingerprint. However, isolates of the same species could not be distinguished. The nested PCR-TTGE approach developed allowed identification of the Glomus species colonising the roots of different plant species.     

入侵豚草与本地植物竞争对丛枝菌根真菌多样性的影响

外来植物入侵常引起入侵地丛枝菌根真菌（arbuscular mycorrhizal fungi,AMF）多样性的变化,但AMF多样性的变化与入侵域本地植物种类相关性目前尚不清楚。本研究采用野外同质园试验研究豚草与不同本地植物竞争时对AMF多样性的影响。本试验共设入侵豚草单种、本地植物狗尾草Setaria viridis单种、藜 Chenopodium album单种、黄香草木犀Melilotus officinalis单种、豚草和狗尾草混种、豚草和藜混种、豚草和黄香草木犀混种以及裸土（无任何植物生长）对照8个处理。采集根区土样后分离、鉴定AMF,分析植株生物量和AMF物种多样性变化间的关系。结果表明,对豚草而言,单种处理中生物量均高于混种处理;豚草分别与3种本地植物竞争时,与黄香草木犀混种中豚草竞争能力最强,而与藜混种中竞争能力最弱。豚草分别与3种本地植物混种时土壤中AMF种丰度和香农-威纳指数分别显著高于豚草单种和本地植物单种,其中豚草与藜混种中AMF的种丰度和香农-威纳指数最高,与狗尾草混种中AMF的种丰度和香农-威纳指数最低,而豚草分别与3种本地植物混种处理中孢子密度显著低于本地植物单种（豚草与黄香草木犀混种除外）。豚草单种、狗尾草单种、藜单种、豚草分别与狗尾草和藜混种4个处理中AMF优势种均为网状球囊霉Glomus reticulatum和缩隔球囊霉Septoglomus constrictum;黄香草木犀单种中优势种是网状球囊霉、缩隔球囊霉和根内根孢囊霉Rhizophagus Intraradices,豚草与黄香草木犀混种中优势种是网状球囊霉和根内根孢囊霉;狗尾草单种、豚草与狗尾草混种和豚草与藜混种3个处理的特有种分别是木薯根孢囊霉Rhizoglomus manihotis、近明球囊霉Claroideoglomus claroideum和美丽盾巨孢囊霉Scutellospora calospora。狗尾草单种生物量与孢子密度呈显著正相关,豚草与狗尾草混种中豚草的生物量与均匀度呈显著负相关,豚草与黄香草木犀混种中豚草的生物量与孢子密度呈显著正相关,与香农威纳指数呈显著负相关。综上可知,豚草与本地植物竞争对AMF多样性的影响具有异质性,这与本地植物种类密切相关。     

Simulated nitrogen deposition affects community structure of arbuscular mycorrhizal fungi in northern hardwood forests

Our previous investigation found elevated nitrogen deposition caused declines in abundance of arbuscular mycorrhizal fungi (AMF) associated with forest trees, but little is known about how nitrogen affects the AMF community composition and structure within forest ecosystems. We hypothesized that N deposition would lead to significant changes in the AMF community structure. We studied the diversity and community structure of AMF in northern hardwood forests after more than 12 years of simulated nitrogen deposition. We performed molecular analyses on maple (Acer spp.) roots targeting the 18S rDNA region using the fungal‐specific primers AM1 and NS31. PCR products were cloned and identified using restriction fragment length polymorphism (RFLP) and sequencing. N addition significantly altered the AMF community structure, and Glomus group A dominated the AMF community. Some Glomus operational taxonomic units (OTUs) responded negatively to N inputs, whereas other Glomus OTUs and an Acaulospora OTU responded positively to N inputs. The observed effect on community structure implies that AMF species associated with maples differ in their response to elevated nitrogen. Given that functional diversity exists among AMF species and that N deposition has been shown to select less beneficial fungi in some ecosystems, this change in community structure could have implications for the functioning of this type of ecosystem.     

丛枝菌根真菌对大气CO2浓度升高和增温响应研究进展

全球变化深刻影响着陆地生态系统生物多样性及生态功能。丛枝菌根(AM)真菌可与绝大多数陆生植物根系形成互惠共生体,在协助宿主养分吸收、促进植物生长、维持植物多样性等方面发挥着重要作用。本文主要分析了大气CO₂浓度升高(eCO₂)和增温对森林和草地生态系统AM真菌群落组成及其功能的影响。eCO₂主要通过影响宿主植物、土壤碳(C)输入等方式间接影响AM真菌,可增加AM真菌的多度和活性,影响AM真菌的多样性与群落组成。增温可直接或间接地(通过宿主植物和土壤途径)影响AM真菌,显著改变森林土壤AM真菌的群落组成,但对草地土壤AM真菌群落组成的影响尚无定论。我们提出了当前研究中存在的主要问题及未来应重点关注的内容。本文旨在明晰AM真菌对eCO₂和增温的响应和适应,增进对AM真菌介导的土壤生态功能的认识,为利用AM真菌缓解全球变化、增强土壤功能的韧性和全球变化的生态系统适应性提供依据。     

西藏高原不同海拔区域丛枝菌根真菌群落的变化

为了进一步了解丛枝菌根(AM)真菌群落对不同海拔环境的响应,基于孢子形态学鉴定,研究了西藏高原不同海拔区域主要草本植物AM真菌的群落特征、菌根侵染及其变化.结果表明: 藏东南低海拔区(2200~3400 m)、藏中中海拔区(3400~3900 m)和藏北高海拔区(4300~5300 m)的AM真菌分别为11属31种、11属20种和6属14种.随着海拔上升,孢子密度(r=0.978,P<0.01)、物种丰度(r=0.462,P>0.05)均趋提高,优势种、特有种比例大幅增加,Shannon指数(r=-0.945,P<0.01)极显著下降.不同海拔区之间AM真菌群落Sorensen相似性系数(0.526~0.592)较为接近,仅在总体上随海拔差异扩大略趋下降;藏东南低海拔区、藏北高海拔区菌根侵染率无显著差异,但均显著低于藏中中海拔区.各海拔区内,不同海拔梯度对AM真菌群落、根系侵染亦具显著影响,但影响程度、影响趋势因整体海拔环境不同而异.说明西藏高原AM真菌群落趋于生境选择,受控于海拔所主导的水热环境及土壤环境.     

锰矿区大叶胡枝子灌丛土壤的丛枝菌根真菌多样性

大叶胡枝子(Lespedeza davidii)为一种豆科灌木,具有较强耐受重金属胁迫及固氮能力,也是矿区一种重要修复植物。丛枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)是一类植物共生真菌,它在矿区与植物共生可促进植物生长、提高植物的抗逆性;但其种类、分布及其影响机制尚不够清楚。以大叶胡枝子灌丛土壤AMF群落为研究对象,采集矿区与非矿区大叶胡枝子冠下及其相邻空旷地土壤进行内部转录间隔区(ITS)测序,分析土壤理化性质,揭示不同样地土壤AMF群落的多样性及其影响因素。研究结果表明:(1)土壤样本共得到2961个可操作分类单元(OTU),其中属于AMF的OTU为66个;Silva数据库比对发现AMF有7目10科16属24种。AMF总体物种丰度为矿区相邻空旷地土壤>矿区冠下土壤>非矿区冠下土壤>非矿区相邻空旷地土壤,Shannon指数和Simpson指数与该趋势保持一致。(2)矿区土壤AMF群落以内养囊霉属(Entrophospora)等为优势属,非矿区冠下以斗管囊霉属(Funneliformis)等为优势属。稀有内养囊霉(Entrophospora infrequens)是4个样地共有的优势种,该种为广谱生态型种;Archaeospora sp.和Paraglomerales sp.为矿区冠下的优势种,它们对锰胁迫有较强的耐受性;Funneliformis sp.为非矿区冠下的优势种。(3)冗余分析(RDA)表明,AMF的种类和数量受到锰含量、土壤pH值以及全磷含量的显著影响。本研究结果说明AMF种类及多样性受到土壤理化性质的影响;矿区一些耐性AMF的存在提高了AMF多样性,它们有利于逆境条件下植物的生长。     

Identification of mycorrhizal fungi from single pelotons of Dactylorhiza majalis (Orchidaceae) using single-strand conformation polymorphism and mitochondrial ribosomal large subunit DNA sequences

The mitochondrial ribosomal large subunit (Ls) DNA was used to identify the orchid mycorrhizal fungi found in roots of Dactylorhiza majalis. The gene was amplified using DNA extracted from single pelotons obtained from fresh and silica gel dried roots. Furthermore, sequencing a variety of well-characterized orchid isolates expanded the fungal database of the mitochondrial ribosomal LsDNA. Polymerase chain reaction product length variants present in D. majalis were sequenced and identified using the expanded database. These analyses revealed two different peloton-forming fungi in samples from D. majalis, which sometimes occurred together as a single two-taxa peloton within the same cortex cell. The first taxon belonged to the genus Tulasnella and the second taxon was distantly related to Laccaria.     

丛枝霸王（Zygophyllum dumosum）根际AM真菌生态学研究

AM真菌是一类广泛分布的土壤真菌,与宿主植物形成共生结构后,对于植物生长和植被恢复有多种有益的生理学和生态学作用。1999年11月至2000年10月,通过每月分别从0－10cm和10－20cm土层采集根际土样,对以色列荒漠地区丛枝霸王（Zygophyllum dumosum Boiss）根际AM真菌进行了系统的生态学研究。AM真菌的分布和定殖与季节变化和采样浓度密切相关。菌根真菌的最高定殖率并不伴随有最大的孢子密度,最高的定殖率发生在1999年11月,而最大的孢子密度则出现在2000年9月。10－20cm土层中的菌根真菌定殖率和孢子密度明显高于0－10cm土层。土壤温度与所有菌根结构的定殖率呈正相关,土壤有机质含量与泡囊和丛枝定殖率呈正相关,而土壤总可溶性氮对泡囊和丛枝定殖有显著正效应,对孢子密度有显著负效应。结果建议,孢子密度、泡囊和丛枝定殖程度可作为检测荒漠土壤状况的生态指标。研究应用于我国特别是西部荒漠地区的植被建立和恢复,可望发挥重任作用：（1）AM真菌能与绝大多数高奶系形成共生联合体,促进根系对土壤矿质营养和水分的吸收,提高植物对干旱、高温、盐碱、根部病害等的抗性,提高逆境条件下植物的成活率,深入研究荒漠生态系统中AM真菌动态分布,以及筛选优势AM菌种和人工接种,进行菌根化育苗,为植被建立和恢复提供优质苗木;（2）菌根的丛枝定殖时间短,主要发生在幼根,泡囊定殖时间长,主要发生在老根,而AM真菌的生长发育和繁殖所需的碳水化合物来自植物根系的分泌活动,所以,通过检测不同时期菌根各种结构的定殖程度和孢子的丰富度,可以获得宿主植物根系的生长状况,进而对土壤环境作出科学的评估。