Association of highly and weakly mycorrhizal seedlings can promote the extra- and intraradical development of a common mycorrhizal network

Arbuscular mycorrhizal fungi (AMF) are key determinants of plant interactions in ecosystems. Through their effects on competition, they are regulators of the structure of communities. Conversely, the composition of plant assemblages may also influence the AMF colonization dynamics of plant species. Here, we tested under in vitro culture conditions the effects of Medicago truncatula, a highly mycorrhizal plant species, and Silene vulgaris, a weakly mycorrhizal plant species, grown single (monospecies treatments) or in combination (bispecies treatment) on the colonization dynamics of the AMF Rhizophagus irregularis MUCL 43194. The seedlings were placed in a pre-established hyphal network developing from a mature M. truncatula mycorrhizal donor plant. Extraradical mycelium (ERM) and root colonization parameters as well as root morphology were measured over a period of 12 days. An increased ERM length, total root colonization and proportion of arbuscules were noted in the bispecies treatment. Conversely, the bispecies treatment seemed to have no effect on root growth. This study also demonstrated the suitability of the in vitro culture system for studying the interactions between AMF and host plants grown as mono- and bispecies combinations.     

低pH对番茄幼苗菌根丛枝形成和磷营养功能的影响

以番茄Solanum lycopersicum为宿主,在pH 4.5和pH 6.5条件下分别接种3种丛枝菌根真菌(AMF),即根内球囊霉Rhizophagus irregularis、珠状巨孢囊霉Gigaspora margarita和脆无梗囊霉Acaulospora delicata,探讨低pH对AMF在根系中的丛枝形成和功能的影响。结果表明,低pH能够显著抑制AMF对根系的侵染以及丛枝的形成;3个菌种之间存在差异,表现为珠状巨孢囊霉的侵染强度最高,根内球囊霉的丛枝丰度对低pH最敏感;AMF显著增加番茄的生物量,降低其根冠比;番茄在pH 6.5的菌根依赖性低于在pH 4.5的对应值,对根内球囊霉的菌根依赖性最低;低pH对碱性磷酸酶(ALP)活性的影响与根系侵染有相似的模式;AMF显著提高地上部磷含量,增强根系LePT4的表达,但pH的影响并不显著。以上结果表明,低pH对AMF与植物共生关系的建立和维持有一定的抑制作用,低pH胁迫条件下AMF的促生作用更大,不同AMF菌种/菌株提高植株低pH抗性的能力存在差异。     

A phosphate transporter from Medicago truncatula involved in the acquisition of phosphate released by arbuscular mycorrhizal fungi

Many plants have the capacity to obtain phosphate via a symbiotic association with arbuscular mycorrhizal (AM) fungi. In AM associations, the fungi release phosphate from differentiated hyphae called arbuscules, that develop within the cortical cells, and the plant transports the phosphate across a symbiotic membrane, called the periarbuscular membrane, into the cortical cell. In Medicago truncatula, a model legume used widely for studies of root symbioses, it is apparent that the phosphate transporters known to operate at the root-soil interface do not participate in symbiotic phosphate transport. EST database searches with short sequence motifs shared by known phosphate transporters enabled the identification of a novel phosphate transporter from M. truncatula, MtPT4. MtPT4 is significantly different from the plant root phosphate transporters cloned to date. Complementation of yeast phosphate transport mutants indicated that MtPT4 functions as a phosphate transporter, and estimates of the K(m) suggest a relatively low affinity for phosphate. MtPT4 is expressed only in mycorrhizal roots, and the MtPT4 promoter directs expression exclusively in cells containing arbuscules. MtPT4 is located in the membrane fraction of mycorrhizal roots, and immunolocalization revealed that MtPT4 colocalizes with the arbuscules, consistent with a location on the periarbuscular membrane. The transport properties and spatial expression patterns of MtPT4 are consistent with a role in the acquisition of phosphate released by the fungus in the AM symbiosis.     

不同施肥处理对丛枝菌根真菌生态分布的影响

研究了在东北海伦实验站长期定位培肥实验地不同施肥处理下丛枝菌根（Arbuscular Mycorrhizal,AM）真菌生长发育状况（包括侵染率、菌丝量和孢子数）,同时还分析了不同施肥处理下AM真菌群落生态分布和特征.结果表明施肥处理,尤其是磷肥（NP2K）处理显著降低AM真菌侵染玉米根系,而根外菌丝长度和孢子数并无显著变化,这和施肥处理下AM真菌的种群结构发生变化有关.随着土壤肥力的增高,土壤中AM真菌种的丰度和密度都有增加的趋势,而当肥力增高到一定程度后（磷肥和钾肥继续增加到NP2K和NPK2处理后）,土壤中AM真菌种的丰度和密度都有下降的趋势;从AM真菌属在不同肥力处理下出现的频度来看,Glomus属在7个处理中出现的频度最高,在每一个肥力处理中都有分布,Acaullospora属次之,Entrohospora属则只是出现在NK处理下;而Glomus属中出现频度最高的种是Glomus mosseae,其次是Glomus caledonium;再次是Glomus diaphanium,这说明施肥处理会影响到AM真菌种属的分布,进而影响到AM真菌的群落结构和生态分布.     

Coexistence of arbuscular mycorrhizae and dark septate endophytic fungi in an undisturbed and a disturbed site of an arid ecosystem

Effect of disturbance on root colonization and vertical distribution of arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) was investigated at two adjacent sites of Lal Suhanra Biosphere Reserve, Pakistan. Disturbance clearly affected AMF and DSE colonization, vertical distribution of AMF and plant community structure. Mean colonization of AMF and DSE was slightly less at the disturbed site. Average spore densities, diversity and richness of AMF and DSE were higher at the undisturbed site. A study of the vertical distribution of AMF associated with the five plant species most common to each study site indicated that beside AMF and DSE colonization disturbance may affect AMF species composition. Correlation of AMF with DSE is also discussed.     

Isolation and characterization of root-specific phosphate transporter promoters from Medicago trunatula

Promoters of phosphate transporter genes MtPT1 and MtPT2 of Medicago truncatula were isolated by utilizing the gene-space sequence information and by screening of a genomic library, respectively. Two reporter genes, beta-glucuronidase (GUS) and green fluorescent protein (GFP) were placed under the control of the MtPT1 and MtPT2 promoters. These chimeric transgenes were introduced into Arabidopsis thaliana and transgenic roots of M. truncatula, and expression patterns of the reporter genes were assayed in plants grown under different phosphate (Pi) concentrations. The expression of GUS and GFP was only observed in root tissues, and the levels of expression decreased with increasing concentrations of Pi. GUS activities in roots of transgenic plants decreased 10-fold when the plants were transferred from 10 microM to 2 mM Pi conditions, however, when the plants were transferred back to 10 microM Pi conditions, GUS expression reversed back to the original level. The two promoters lead to different expression patterns inside root tissues. The MtPT1 promoter leads to preferential expression in root epidermal and cortex cells, while MtPT2 promoter results in strong expression in the vascular cylinder in the center of roots. Promoter deletion analyses revealed possible sequences involved in root specificity and Pi responsiveness. The promoters are valuable tools for defined engineering of plants, particularly for root-specific expression of transgenes.     

The effect of flavones and flavonols on colonization of tomato plants by arbuscular mycorrhizal fungi of the genera Gigaspora and Glomus

No clear data are available on how flavonoids from different chemical groups affect root colonization by arbuscular mycorrhizal fungi (AMF) and whether flavonoids affecting the presymbiotic growth of AMF also affect root colonization by AMF. In the present work, we compared the effect of flavones (chrysin and luteolin) and flavonols (kaempferol, morin, isorhamnetin, and rutin) on root colonization (number of entry points and degree of root colonization) of tomato plants (Lycopersicum esculentum L.) with the effect of these flavonoids on the presymbiotic growth of these AMF, which has been reported in a recent study. With all tested AMF (Gigaspora rosea, Gigaspora margarita, Glomus mosseae, and Glomus intraradices) a correlation between the number of entry points and the percentage of root colonization was found. When the number of entry points was high, root colonization was also enhanced. Application of the flavones chrysin and luteolin and of the flavonol morin increased the number of entry points and the degree of colonization,whereas the flavonols kaempferol, isorhamnetin, and rutin showed no effect. These results show that in contrast to their effect on the presymbiotic growth of the AMF on the level of root colonization, the tested flavonoids do not exhibit a genus- and species-specificity. Moreover, comparison of our data with the data obtained by J.M. Scervino, M.A. Ponce, R. Erra-Bassells, H. Vierheilig, J.A. Ocampo, and A. Godeas. (2005a. J. Plant Interact. 15: 22-30) indicates that a positive effect on the hyphal growth of AMF does not necessarily result in an enhanced AM root colonization, further indicating that the mode of action of flavonoids at the level of root colonization is more complex.     

Wetland dicots and monocots differ in colonization by arbuscular mycorrhizal fungi and dark septate endophytes

As an initial step towards evaluating whether mycorrhizas influence composition and diversity in calcareous fen plant communities, we surveyed root colonization by arbuscular mycorrhizal fungi (AMF) and dark septate endophytic fungi (DSE) in 67 plant species in three different fens in central New York State (USA). We found colonization by AMF and DSE in most plant species at all three sites, with the type and extent of colonization differing between monocots and dicots. On average, AMF colonization was higher in dicots (58±3%, mean±SE) than in monocots (13±4%) but DSE colonization followed the opposite trend (24±3% in monocots and 9±1% in dicots). In sedges and cattails, two monocot families that are often abundant in fens and other wetlands, AMF colonization was usually very low (<10%) in five species and completely absent in seven others. However, DSE colonization in these species was frequently observed. Responses of wetland plants to AMF and DSE are poorly understood, but in the fen communities surveyed, dicots appear to be in a better position to respond to AMF than many of these more abundant monocots (e.g., sedges and cattails). In contrast, these monocots may be more likely to respond to DSE. Future work directed towards understanding the response of these wetland plants to AMF and DSE should provide insight into the roles these fungal symbionts play in influencing diversity in fen plant communities.     

Arbuscular mycorrhizal fungi differ in affecting the flowering of a host plant under two soil phosphorus conditions

Aims Studies have showed that arbuscular mycorrhizal fungi (AMF) can greatly promote the growth of host plants, but how AMF affect flowering phenology of host plants is not well known. Here, we conducted a pot experiment to test whether life cycle and flowering phenology traits of host plant Medicago truncatula Gaertn can be altered by AMF under low and high soil phosphorus (P) levels.Methods The experiment was conducted in a greenhouse at Zhejiang University in China (120°19′E, 30°26′N) and had a completely randomized design with two factors: AMF treatments and soil P levels. Six AMF species (Acaulospora scrobiculata, As; Gigaspora margarita, Gma; Funneliformis geosporum, Fg; Rhizophagus intraradices, Ri; Funneliformis mosseae, Fmo and Glomus tortuosum, Gt.) were used, and two soil P levels (24.0 and 5.7 mg kg^-1 Olsen-soluble P) were designed. The six AMF species were separately inoculated or in a mixture (Mix), and a non-AMF control (NAMF) was included. When plants began to flower, the number of flowers in each pot was recorded daily. During fruit ripening, the number of mature fruits was also recorded daily. After ~4 months, the biomass, biomass P content and AMF colonization of host plant were measured. Correlation between root colonization and first flowering time, or P content and first flowering time was analyzed.Important findings Under the low P level, first flowering time negatively correlated with root colonization and biomass P. Only host plants with AMF species As, Fg, Ri, or Mix were able to complete their life cycle within 112 days after sowing. And treatment with AMF species Fg, Gt, or As resulted in two periods of rapid flower production while other fungi treatments resulted in only one within 112 days after sowing. The cumulative number of flowers produced and biomass P content were highest with species Fg. Host biomass allocation significantly differed depending on the species of AMF. Under both soil P levels, the host plant tended to allocate more biomass to fruits in the Mix treatment than in the other treatments. These results indicated that the effects of AMF on host flowering phenology and biomass allocation differed depending on AMF species and soil P levels.     

Influence of arbuscular mycorrhizal colonization on whole‐plant respiration and thermal acclimation of tropical tree seedlings

Symbiotic arbuscular mycorrhizal fungi (AMF) are ubiquitous in tropical forests. AMF play a role in the forest carbon cycle because they can increase nutrient acquisition and biomass of host plants, but also incur a carbon cost to the plant. Through their interactions with their host plants they have the potential to affect how plants respond to environmental perturbation such as global warming. Our objective was to experimentally determine how plant respiration rates and responses to warmer environment are affected by AMF colonization in seedlings of five tropical tree species at the whole plant level. We evaluated the interaction between AMF colonization and temperature on plant respiration against four possible outcomes; acclimation does or does not occur regardless of AMF, or AMF can increase or decrease respiratory acclimation. Seedlings were inoculated with AMF spores or sterilized inoculum and grown at ambient or elevated nighttime temperature. We measured whole plant and belowground respiration rates, as well as plant growth and biomass allocation. There was an overall increase in whole plant, root, and shoot respiration rate with AMF colonization, whereas temperature acclimation varied among species, showing support for three of the four possible responses. The influence of AMF colonization on growth and allocation also varied among plant species. This study shows that the effect of AMF colonization on acclimation differs among plant species. Given the cosmopolitan nature of AMF and the importance of plant acclimation for predicting climate feedbacks a better understanding of the patterns and mechanisms of acclimation is essential for improving predictions of how climate warming may influence vegetation feedbacks.     

N-P fertilization did not reduce AMF abundance or diversity but alter AMF composition in an alpine grassland infested by a root hemiparasitic plant

Fertilization has been shown to have suppressive effects on arbuscular mycorrhizal fungi (AMF) and root hemiparasites separately in numerous investigations, but its effects on AMF in the presence of root hemiparasites remain untested. In view of the contrasting nutritional effects of AMF and root hemiparasites on host plants, we tested the hypothesis that fertilization may not show strong suppressive effects on AMF when a plant community was infested by abundant hemiparasitic plants. Plants and soil samples were collected from experimental field plots in Bayanbulak Grassland, where N and P fertilizers had been applied for three continuous years for control against a spreading root hemiparasite, Pedicularis kansuensis. Shoot and root biomass of each plant functional group were determined. Root AMF colonization levels, soil spore abundance, and extraradical hyphae length density were measured for three soil depths (0-10 cm, 10-20 cm, 20-30 cm). Partial 18S rRNA gene sequencing was used to detect AMF diversity and community composition. In addition, we analyzed the relationship between relative abundance of different AMF genera and environmental factors using Spearman's correlation method. In contrast to suppressive effects reported by many previous studies, fertilization showed no significant effects on AMF root colonization or AMF species diversity in the soil. Instead, a marked increase in soil spore abundance and extraradical hyphae length density were observed. However, fertilization altered relative abundance and AMF composition in the soil. Our results support the hypothesis that fertilization does not significantly influence the abundance and diversity of AMF in a plant community infested by P. kansuensis.     

Arbuscular mycorrhizal fungi enhance the growth of the exotic species Ambrosia artemisiifolia

丛枝菌根真菌促进外来植物豚草的生长 丛枝菌根真菌(AMF)可以通过其菌丝增加寄主植物对养分的吸收,从而促进植物生长。丛枝菌根真菌一直与大多数外来植物的成功入侵联系在一起。然而,有关丛枝菌根真菌如何影响植物入侵成功的机制仍然有待研究。豚草(Ambrosia artemisiifolia)是一种外来的菌根植物。通过长期田间实验,我们研究了种间竞争对豚草和狗尾草(Setaria viridis)根系丛枝菌根真菌多样性和组成的影响。此外,在温室实验中探究了摩西球囊霉(Funneliformis mosseae)对这两种植物生长的影响。研究结果表明,豚草入侵改变了本地植物狗尾草根系丛枝菌根真菌的多样性。另外,豚草根系中摩西球囊霉的相对多度显著高于狗尾草根系中。在田间和温室实验中均发现外来种豚草的丛枝菌根真菌侵染率高于本地种狗尾草。温室实验结果表明,丛枝菌根真菌通过影响豚草的光合能力以及磷和钾的吸收而促进豚草生长。这些研究结果揭示了丛枝菌根真菌和豚草成功入侵之间的重要关系。     

大兴安岭落叶松林丛枝菌根真菌多样性

对大兴安岭落叶松林17个科26种植物丛枝菌根(AM)定居情况和丛枝菌根真菌(AMF)多样性进行了调查。在26种植物根样中形成典型AM定居的有23种,占88.46%。菌根侵染率为0～78.7%,平均为21.69%。在26种植物根样中,4种植物形成重楼型(Par-is-type)AM,占15.38%;10种植物形成疆南星型(Arum-type)AM,占38.46%;9种植物形成中间型(Intermediatetype)AM,占34.62%,3种植物未能形成AM菌根,占11.54%。从23种植物根围土样中分离到50种AMF,分属于5个属,其中无梗囊霉属(Acaulospora)24种占48%;球囊霉属(Glomus)19种占38%;内养囊霉属(Entrophospora)5种占10%;原囊霉属(Archaeospora)1种占2%;巨孢囊霉属(Gigaspora)1种占2%。Acaulospora和Glomus2属真菌在大兴安岭落叶松林土壤中占绝对优势;尼氏无梗囊霉(A.nocolsonii)和幼套球囊霉(G.etunicatum)是优势种。植物根围土壤中AMF的孢子密度平均为68.94个.100g-1风干土;AM...     

Arbuscular mycorrhizal fungi in two mangroves in South China

The symbiosis between arbuscular mycorrhizal fungi (AMF) and mangrove plant species was investigated in two mangrove swamps in south China. AMF were mostly found in the form of hyphae and were commonly associated with all the mangrove species we investigated. Six AMF species belonging to the genera Glomus or Acaulospora were identified. Multiple step-wise linear regression analyses showed that hydrological conditions and phosphorus levels in the rhizosphere were the main abiotic factors affecting the colonization of mangrove species by AMF. A greenhouse experiment was conducted to evaluate the effects of AMF inoculation on the growth and nutrient uptake of a true mangrove plant species, Sonneratia apetala B. Ham. The inoculated AMF significantly improved growth, resulting in greater plant height, diameter at ground level and plant biomass, as well as increased absorption of N, P and K. These findings suggest that AMF play important roles in mangrove ecosystems.     

Rapid top–down regulation of plant C:N:P stoichiometry by grasshoppers in an Inner Mongolia grassland ecosystem

Mosses play an integral role in the hydrologic regimes of ecosystems where they cover the soil surface, and thus affect biogeochemical cycling of elements influenced by soil oxidation–reduction (redox) reactions, including the plant growth-limiting nutrients, nitrogen and phosphorus (P). In rich fens where P often limits plant growth, we hypothesized that feedbacks between mosses and redox conditions would determine P availability to shallow-rooted forb species that constitute much of these wetlands’ unusually high plant species diversity. In a moss removal experiment in three fens, forb tissue P and microbial P were greater while anion exchange membrane (AEM) resin P was lower where mosses occurred than where they were removed, suggesting both higher availability and greater demand for P in moss-covered soils. Coupled physicochemical and biological mechanisms drove moss effects on P cycling, ultimately through effects on soil oxygenation or reduction: higher redox potential underlying mosses corresponded to greater microbial activity, phosphatase enzyme activity, and colonization by arbuscular mycorrhizal fungi (AMF), all of which can promote greater P availability to plants. These more oxidized soils stimulated: (1) greater microbial activity and root vigor; (2) correspondingly greater P demand via microbial uptake, forb uptake, and iron (Fe)-P reactions; and (3) greater P supply through soil and root phosphatase activity and AMF colonization. This work demonstrates that mosses improve vascular plant P acquisition by alleviating stresses caused by reducing conditions that would otherwise prevail in shallow underlying soils, thus providing a mechanism by which mosses facilitate plant species diversity in rich fens.