Increased photosynthetic acclimation in alfalfa associated with arbuscular mycorrhizal fungi (AMF) and cultivated in greenhouse under elevated CO2

Medicago sativa L. (alfalfa) can exhibit photosynthetic down-regulation when grown in greenhouse conditions under elevated atmospheric CO₂. This forage legume can establish a double symbiosis with nitrogen fixing bacteria and arbuscular mycorrhizal fungi (AMF), which may increase the carbon sink effect of roots. Our aim was to assess whether the association of alfalfa with AMF can avoid, diminish or delay the photosynthetic acclimation observed in previous studies performed with nodulated plants. The results, however, showed that mycorrhizal (M) alfalfa at the end of their vegetative period had lower carbon (C) discrimination than non-mycorrhizal (NM) controls, indicating photosynthetic acclimation under ECO₂ in plants associated with AMF. Decreased C discrimination was due to the acclimation of conductance, since the amount of Rubisco and the expression of genes codifying both large and small subunits of Rubisco were similar or slightly higher in M than in NM plants. Moreover, M alfalfa accumulated a greater amount of soluble sugars in leaves than NM plants, thus favoring a down-regulation effect on photosynthetic rates. The enhanced contents of sugars in leaves coincided with a reduced percentage of arbuscules in roots, suggesting decreased sink of carbohydrates from shoots to roots in M plants. The shorter life cycle of alfalfa associated with AMF in comparison with the NM controls may also be related to the accelerated photosynthetic acclimation in M plants. Further research is needed to clarify to what extent this behavior could be extrapolated to alfalfa cultivated in the field and subjected to periodic cutting of shoots under climatic change scenarios.     

Biolistic transformation of arbuscular mycorrhizal fungi

Gene transfer systems have proved effective for the transformation of a range of organisms for both fundamental and applied studies. Biolistic transformation is a powerful method for the gene transfer into various organisms and tissues that have proved recalcitrant to more conventional means. For fungi, the biolistic approach is particularly effective where protoplasts are difficult to obtain and/or the organisms are difficult to culture. This is particularly applicable to arbuscular mycorrhizal (AM) fungi, being as they are obligate symbionts that can only be propagated in association with intact plants or root explants. Furthermore, these fungi are aseptate and protoplasts cannot be released. Recent advancements in gene transformation systems have enabled the use of biolistic technology to introduce foreign DNA linked to molecular markers into these fungi. In this review we discuss the development of transformation strategies for AM fungi by biolistics and highlight the areas of this technology which require further development for the stable transformation of these elusive organisms.     

不同积雪覆盖期荒漠齿肋赤藓结皮层丛枝菌根真菌多样性变化

【背景】温带荒漠有积雪背景条件下的荒漠苔藓植物与丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)共生关系的研究非常有限。【目的】揭示不同积雪覆盖期(降雪前、雪盖期、融雪期)齿肋赤藓结皮层中AMF多样性的差异,为正确认识荒漠特色植物与微生物在冬季积雪期互利的重要生存策略提供数据支撑。【方法】利用高通量测序技术,分析稳定积雪期的古尔班通古特沙漠优势苔藓齿肋赤藓结皮AMF群落组成与多样性状况,尤其是降雪前和融雪期AMF群落结构差异。【结果】降雪前、雪盖期及融雪期检测到的OTU分属于球囊菌门(Glomeromycota)的5目9科11属,其中,近明球囊霉属(Claroideoglomus)、原囊霉属(Archaeospora)、类球囊霉属(Paraglomus)和球囊霉属(Glomus)为优势类群;降雪前和融雪期齿肋赤藓结皮层中绝对优势属(>50%)均为近明球囊霉属。群落丰富度Chao1指数和ACE指数均表现为雪盖前>积雪期>融雪期,表明降雪减少了AMF群落丰富度。近明球囊霉属融雪期比例大幅增加,而类球囊霉属、球囊霉属则较降雪前比例下降。基于MEGAN的分类学组成信息可视化分析表明,低丰度AMF类群更容易受到影响,无梗囊霉属(Acaulospora)主要集中在降雪前采集的样品中,而多样孢囊霉属(Diversispora)主要集中在融雪期样品中。结合聚类分析的属水平群落组成热图发现,高丰度分类单元的类别由降雪前的5种集中为2种。主成分分析结果表明,主成分1能够区分降雪前后的AMF群落结构特征,进一步验证降雪缺失对藓类结皮层AMF群落组成有筛选作用。高丰度优势属近明球囊霉属和球囊霉属之间、类球囊霉属和原囊霉属之间均呈现负相关,可能存在竞争关系;低丰度属巨孢囊霉属(Gigaspora)、隔球囊霉属(Septoglomus)、双型囊霉属(Ambispora)、盾巨孢囊霉属(Scutellospora)呈现正相关,可能存在协作关系以适应降雪。【结论】古尔班通古特沙漠的冬季降雪对苔藓结皮层AMF类群中的优势属和低丰度属有不同的选择策略。融雪期绝对优势属会降低存在竞争关系优势属的比例,进一步巩固优势地位,而存在正相关的低丰度属会同步降低比例,而且苔藓结皮层AMF优势属在该沙漠为近明球囊霉属。     

Effects of nicosulfuron on the abundance and diversity of arbuscular mycorrhizal fungi used as indicators of pesticide soil microbial toxicity

The key role of arbuscular mycorrhizal (AM) fungi in maintaining soil fertility and ecosystem functioning and their general sensitivity to pesticides make them good candidate bioindicators in pesticide soil microbial toxicity assessment. We investigated the impact of the herbicide nicosulfuron on mycorrhizal colonization and community structure of AM fungi via a pot-to-field experimental approach. This allowed the assessment of nicosulfuron toxicity (i) at extreme exposure schemes (pot experiment, Tier I) invoked by the repeated application of a range of dose rates (x0, x10, x100, x1000 the recommended dose) and (ii) under realistic exposure scenarios (x0, x1, x2, x5 the recommended dose) in the field (Tier II). In the pot experiment, the x100 and x1000 dose rates significantly reduced plant biomass, mycorrhizal colonization and AM fungal richness as determined by DGGE. This coincided with the progressive accumulation of herbicide concentrations in soil. In contrast, no effects on AM fungi were observed at the nicosulfuron dose rates tested in the field. Clone libraries showed that the majority of AM fungi belonged to the Glomus group and were sensitive to the high levels of nicosulfuron accumulated in soil at the latter culture cycles. In contrast, a Paraglomeraceae and a Glomus etunicatum ribotype were present in maize roots in all cycles and dose rates implying a tolerance to nicosulfuron-induced stress. Overall, the deleterious effects of nicosulfuron on AM fungi induced by the highest dose rates in the pot experiment could be attributed either to fungal-driven toxicity or to plant-driven effects which have subsequent implications for mycorrhizal symbiosis. We suggest that the tiered pot-to-field experimental approach followed in our study combined with classic and standardized molecular tools could provide a realistic assessment of the toxicity of pesticides onto AM fungi as potential bioindicators.     

Red list plants: colonization by arbuscular mycorrhizal fungi and dark septate endophytes

Since information concerning the mycorrhization of endangered plants is of major importance for their potential re-establishment, we determined the mycorrhizal status of Serratula tinctoria (Asteraceae), Betonica officinalis (Lamiaceae), Drosera intermedia (Droseraceae) and Lycopodiella inundata (Lycopodiaceae), occurring at one of two wetland sites (fen meadow and peat bog), which differed in soil pH and available P levels. Root colonization by arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) was quantified. Colonization by AMF appeared to be more frequent in the fen meadow than in the peat bog, and depended on the host plant. Roots of S. tinctoria and B. officinalis were well colonized by AMF in the fen meadow (35–55% root length) and both arbuscules and vesicles were observed to occur in spring as well as in autumn. In the peat bog, L. inundata showed a low level of root colonization in spring, when vesicles were found frequently but no arbuscules. In roots of D. intermedia from the peat bog, arbuscules and vesicles were observed, but AMF colonization was lower than in L. inundata. In contrast, the amount of AMF spores extracted from soil at the peat bog site was higher than from the fen meadow soil. Spore numbers did not differ between spring and autumn in the fen meadow, but they were higher in spring than in autumn in the peat bog. Acaulospora laevis or A. colossica and Glomus etunicatum were identified amongst the AMF spores extracted from soil at the two sites. S. tinctoria and B. officinalis roots were also regularly colonized by DSE (18–40% root length), while L. inundata was only rarely colonized and D. intermedia did not seem to be colonized by DSE at all.     

龙脑香科植物对丛枝菌根真菌的影响

在天然林地和温室盆栽条件下,比较研究了龙脑香科植物对丛枝菌根(Arbuscular mycorrhizas,AM)真菌孢子密度、相对多度、频度、属的组成、丰度和侵染状况等方面的影响.结果表明,用坡垒作盆栽寄主加富培养后,菌根侵染率、泡囊、丛枝和侵入点都低于原采样植物,以原坡垒土壤中栽植苗木的侵染率为最高,可达20.3%;而以望天树根围土壤栽植的苗木为最低,仅为10.6%;坡垒还不同程度地改变了原采样植物根围土壤中AM真菌孢子的密度、相对多度、频度、属的组成、丰度等.在4种土壤中,栽植坡垒苗木后,AM真菌的孢子密度都有不同程度的增长.采用与原采样相同种类的植物作为AM真菌加富培养的寄主更有利于促进AM真菌的生长发育、保持AM的多样性.     

中国大陆地区丛枝菌根真菌菌种资源的分离鉴定与形态学特征

【目的】分离收集保藏中国大陆各个地区不同生态环境的丛枝菌根真菌菌种资源,为丛枝菌根的研究提供资源、奠定基础。【方法】以高粱为宿主植物,采用诱导培养、单孢培养和扩繁培养分离土壤样品中的丛枝菌根真菌菌种并鉴定。【结果】从我国大陆的45个地区50余种宿主植物根区土壤中分离到丛枝菌根真菌135株,隶属于23个种;对各个菌株的形态特征进行了描述。【结论】我国蕴藏着丰富的丛枝菌根真菌菌种资源,文中描述的菌种资源是目前从我国大陆地区获得的种类和数量最多、覆盖范围最广的AM真菌菌种资源。     

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.     

Effects of mowing on fungal endophytes and arbuscular mycorrhizal fungi in subalpine grasslands

In French subalpine grasslands, cessation of mowing promotes dominance of Festuca paniculata, which alters plant diversity and ecosystem functioning. One of the mechanisms underpinning such effects may be linked to simultaneous changes in the abundance of fungal symbionts such as endophytes and arbuscular mycorrhizal fungi. In field conditions, mowing reduced the abundance of the endophyte Neotyphodium sp. in leaves of F. paniculata by a factor of 6, and increased mycorrhizal densities by a factor of 15 in the soil. In greenhouse experiments, the mycorrhizal colonization of Trifolium pratense and Allium porrum increased 3- fold and 3.8- fold respectively in mown vs unmown grassland soil. Significantly reduced growth of the two host plants was also observed on soil from the unmown grassland. Such opposite effects of mowing on the two functional groups of fungal symbionts could suggest interactions between these two groups, which in turn could contribute to structuring plant communities in subalpine grasslands.     

Genetic processes in arbuscular mycorrhizal fungi

Arbuscular mycorrhizal (AM) fungi (Glomeromycota) colonize roots of the majority of land plants and facilitate their mineral nutrient uptake. Consequently, AM fungi play an important role in terrestrial ecosystems and are becoming a component of sustainable land management practices. The absence of sexual reproductive structures in modern Glomeromycota combined with their long evolutionary history suggest that these fungi may represent an ancient asexual lineage of great potential interest to evolutionary biology. However, many aspects of basic AM fungal biology, including genome structure, within-individual genetic variation, and reproductive mode are poorly understood. These knowledge gaps hinder research on the mechanisms of AM fungal interactions with individual plants and plant communities, and utilization of AM fungi in agricultural practices. I present here the current state of research on the reproduction in AM fungi and indicate what new findings can be expected in the future.     

丛枝菌根真菌物种多样性研究进展

丛枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)在不同生态系统均发挥至关重要的作用,研究其多样性能够为AMF物种资源的保护和利用提供科学依据。AMF不能被离体纯培养以及自身的高变异性等因素严重阻碍了对其进行深入研究,随着研究方法的不断改进,尤其是新一代测序技术的运用,极大加速了人们对AMF物种多样性的认识。本文主要从AMF分类系统、不同宿主植物和不同生境中的AMF物种多样性及AMF物种多样性研究方法(包括形态鉴定、Sanger测序和高通量测序)方面介绍AMF物种多样性研究进展,并且探讨AMF物种多样性研究中存在的主要问题,认为在今后AMF物种多样性研究中不仅要注重运用新的研究手段,还应该着重解决AMF不能离体纯培养的问题。     

丛枝菌根真菌影响作物非生物胁迫耐受性的研究进展

土壤中存在着大量不同种类的微生物资源,土壤微生物能够与自然界中的大多数植物密切合作,其中丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)起着十分重要的作用。近年来,对于AMF的研究越来越多。AMF是存在于土壤中的重要真菌之一,是土壤中的菌根真菌菌丝与高等植物营养根系形成的一种联合体。AMF可以与陆地上90%左右的植物根系形成共生体,通过在植物根系形成重要的“丛枝菌根”结构而为植物提供更多的养分。为了了解接种AMF对作物生长过程中耐受一些非生物胁迫(如干旱、极端温度、重金属污染、盐分、不利的土壤pH变化等)性能方面的影响,基于之前接种AMF对养分胁迫下玉米生长影响的研究,在扩大作物品种的基础上,通过查阅大量文献,结合试验研究及对前人和近年来关于AMF的一些最新研究进展,获得了具有实践性意义的新发现：AMF与植物共生有助于植物生长,可以改善植物的营养状况,并且可以保护植物免受各种非生物环境胁迫的影响。由此可以得出结论：AMF通过各种机制改善植物生长状况,提高作物抗逆性,为作物增产、农民增收创造了福利,并且避免了由于肥料过量施用导致的一些污染环境问题。本文主要综述了接种AMF在各种非生物环境胁迫(干旱、极端温度、重金属污染、盐分、不利的土壤pH变化等)条件下对植株生长和发育的有利影响,并对目前存在的不足和今后研究的重点提出几点建议。     

Associations between arbuscular mycorrhizal fungi and Rhynchrelyrum repens in abandoned quarries in southern China

The association between arbuscular mycorrhizal fungi (AMF) and Rhynchrelyrum repens was investigated. In six abandoned quarries in the Pearl River Delta area, R. repens was found to be associated with nine AMF species, including Glomus versiforme, G. brohultii, G. microaggregatum, G. clarum and G. claroideum, Acaulospora delicata, A. mellea, A. mollowae and Entrophospora infrequens. The genus Glomus and the species G. brohultii were recorded at the highest frequencies. Three typical arbuscular mycorrhizal (AM) structures, i.e. hyphae, vesicles and arbuscules, were found in the roots of the R. repens specimens collected from all the quarries investigated. Vesicles were the most frequently recorded structure. Results of a container-based experiment showed that R. repens had very high mortality (83.3%) in the absence of AMF in soil containing sufficient P (phosphorus); this indicates that R. repens is an obligate mycotroph. The presence of AMF significantly increased the biomass accumulation of R. repens seedlings (p < 0.01). It was also observed that AMF colonization was related to soil P and K (potassium) utilization by R. repens seedlings. It is, therefore, important to inoculate with AMF when using R. repens for the restoration of damaged ecosystems.     

不同丛枝菌根真菌对万寿菊生长及柴油降解率的影响

在盆栽条件下,用沈抚污灌区非灭菌水稻土,研究了柴油浓度为5000mg·kg^1时接种3种AM真菌(Glomus mosseae,G.geospora,G.constrictum)和细菌对万寿菊(Tagetes erecta)耐油性的影响。结果表明,在此浓度下,AM菌仍能和万寿菊形成共生体,白色万寿菊比黄色万寿菊耐油能力强,总生物量增加63．1％;接种AM真菌的处理,其侵染率比对照高3．5％～29．9％．G．masseae和G．geospora是较好的菌种,总生物量分别比对照增加9．0％和42．7％;混接AM真菌效果一般。施入细菌菌剂虽然抑制了AM菌对万寿菊的侵染,但促进了菌根化植物的营养生长和生殖生长,5种接菌处理中,以接种G．geospora和混接AM菌和细菌的处理最好,对柴油的降解率分别比对照增加16．51％和14．05％。     

丛枝菌根真菌对小麦生长的影响

为了促进经济作物小麦的生长,提高土壤氮磷循环与转化效率,选择两种优良丛枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)——摩西球囊霉(GM,Glomus mosseae)、根内球囊霉(GI,Glomus intraradices),研究AMF在小麦整个营养生长阶段中对其生长以及对土壤中植物生长需求的大量元素——氮、磷的作用及影响。结果表明:人工施加菌剂可显著提高AMF对小麦的侵染率,施加GM菌剂时,小麦侵染率提高24.54%,同时,株高提高14.08%,小麦地上生物量提高24.05%。GM效果优于GI。施加菌剂后,小麦侵染率与土壤中水解性氮呈显著正相关;植物地上生物量与土壤中总氮,水解性氮呈显著负相关。表明AMF可活化土壤中的氮元素,同时促进作物生长,强化对土壤中氮元素的利用。     

中国盐碱土壤中AM菌的生态分布

对我国盐碱土壤中丛枝菌根（Ａｒｂｕｓｃｕｌａｒ Ｍｙｃｏｒｒｈｉｚａ,ＡＭ） 菌的种属构成、生态分布状况进行了研究．结果表明,不同地区ＡＭ 菌种属构成不同,其种属组成、分布与土壤类型、碱化度和土壤有机质含量有关．盐渍化砂土、壤土和粘土中,Ｇｌｏｍｕｓ 属的真菌数量最多,Ａｃａｕｌｏｓｐｏｒａ 属次之,而Ｇｌｏｍｕｓ 属中的Ｇ．ｍｏｓｓｅａｅ 则是分布最为广泛的菌种．随土壤碱化度的增加,Ｇｌｏｍｕｓ ｍｏｓｓｅａｅ 出现频率随之相对增加．在一定范围内有机质含量越高,土壤中ＡＭ 菌种和属的种类就越多．ＡＭ 菌的种属组成因不同寄主植物而异,其中豆科植物根围中ＡＭ 菌分布的种属数量最多．     

Status of arbuscular mycorrhizal fungi (AMF) in the Sundarbans of India in relation to tidal inundation and chemical properties of soil

The arbuscular mycorrhizal status of fifteen mangroves and one mangrove associate was investigated from 27 sites of three inundation types namely, diurnal, usual springtide and summer springtide. Roots and rhizospheric soil samples were analysed for spore density, frequency of mycorrhizal colonization and some chemical characteristics of soil. Relative abundance, frequency and spore richness of AMF were assessed at each inundation type. All the plant species except Avicennia alba exhibited mycorrhizal colonization. The study demonstrated that mycorrhizal colonization and spore density were more influenced by host plant species than tidal inundation. Forty four AMF species belonging to six genera, namely Acaulospora, Entrophospora, Gigaspora, Glomus, Sclerocystis and Scutellospora, were recorded. Glomus mosseae exhibited highest frequency at all the inundation types; Glomus fistulosum, Sclerocystis coremioides and Glomus mosseae showed highest relative abundance at sites inundated by usual springtides, summer springtides and diurnal tides, respectively. Spore richness of AMF was of the order usual springtide > diurnal > summer springtide inundated sites. The mean spore richness was 3.27. Diurnally inundated sites had the lowest concentrations of salinity, available phosphorus, exchangeable potassium, sodium and magnesium. Statistical analyses indicated that mycorrhizal frequency and AMF spore richness were significantly negatively correlated to soil salinity. Spore richness was also significantly negatively correlated to available phosphorus. The soil parameters of the usual springtide inundated sites appeared to be favourable for the existence of maximum number of AMF. Glomus mosseae was the predominant species in terms of frequency in the soils of the Sundarbans.     

Seasonal dynamics of arbuscular mycorrhizal fungi in differing wetland habitats

The dynamics and role of arbuscular mycorrhizal fungi (AMF) have been well described in terrestrial ecosystems; however, little is known about how the dynamics of AMF are related to the ecology of wetland ecosystems. The seasonal dynamics of arbuscular mycorrhizal (AM) colonization within different wetland habitats were examined in this study to determine the factors that influence AM associations and to further assess the ecological role of AMF in wetlands. Fen and marsh habitats of four wetlands in west central Ohio were sampled monthly from March to September. AMF were found at all four sites for each month sampled and were present in all of the dominant plant species. A significant effect of month (P<0.001) on AM colonization did occur and was attributable to maximum colonization levels in the spring and minimum levels in late summer. This trend existed in all four wetlands in both fen and marsh habitats, regardless of variation in water levels, percent soil moisture, or available phosphorus levels. Because abiotic factors had minimal influence on AM colonization variation and the level of AM colonization paralleled plant growth patterns, we conclude that the AM seasonal dynamic was in response to plant phenology. Our data suggest that AM associations in temperate fen and marsh habitats are prevalent in the spring during new root and vegetative growth, even for plants experiencing flooded conditions. Evidence of an overriding AM seasonal trend indicates that future studies should include a seasonal component to better assess the role and distribution of AMF in wetland ecosystems.     

The mycorrhizal dependence of subordinates determines the effect of arbuscular mycorrhizal fungi on plant diversity

It is widely recognized that arbuscular mycorrhizal fungi (AMF) influence plant community structure. Several studies in the past few years have focused on the effect of AMF on plant diversity, showing contradictory results. On the basis of studies carried out in grasslands, it has been proposed that these results may not be in conflict but rather depend on mycorrhizal dependence of dominant and subordinate species in the plant community. Here, we propose a simple conceptual model to explain the effect of AMF on plant diversity and dominance hierarchy. Our model suggests that the effect of AMF on plant diversity can be explained mainly by mycorrhizal dependence of subordinates. It also gives predictions for a wider range of community types, and helps in identifying the systems in which empirical data are most critically needed.