Community structure of arbuscular mycorrhizal fungi associated with Robinia pseudoacacia in uncontaminated and heavy metal contaminated soils

The significance of arbuscular mycorrhizal fungi (AMF) in soil remediation has been widely recognized because of their ability to promote plant growth and increase phytoremediation efficiency in heavy metal (HM) polluted soils by improving plant nutrient absorption and by influencing the fate of the metals in the plant and soil. However, the symbiotic functions of AMF in remediation of polluted soils depend on plant–fungus–soil combinations and are greatly influenced by environmental conditions. To better understand the adaptation of plants and the related mycorrhizae to extreme environmental conditions, AMF colonization, spore density and community structure were analyzed in roots or rhizosphere soils of Robinia pseudoacacia. Mycorrhization was compared between uncontaminated soil and heavy metal contaminated soil from a lead–zinc mining region of northwest China. Samples were analyzed by restriction fragment length polymorphism (RFLP) screening with AMF-specific primers (NS31 and AM1), and sequencing of rRNA small subunit (SSU). The phylogenetic analysis revealed 28 AMF group types, including six AMF families: Glomeraceae, Claroideoglomeraceae, Diversisporaceae, Acaulosporaceae, Pacisporaceae, and Gigasporaceae. Of all AMF group types, six (21%) were detected based on spore samples alone, four (14%) based on root samples alone, and five (18%) based on samples from root, soil and spore. Glo9 (Rhizophagus intraradices), Glo17 (Funneliformis mosseae) and Acau3 (Acaulospora sp.) were the three most abundant AMF group types in the current study. Soil Pb and Zn concentrations, pH, organic matter content, and phosphorus levels all showed significant correlations with the AMF species compositions in root and soil samples. Overall, the uncontaminated sites had higher species diversity than sites with heavy metal contamination. The study highlights the effects of different soil chemical parameters on AMF colonization, spore density and community structure in contaminated and uncontaminated sites. The tolerant AMF species isolated and identified from this study have potential for application in phytoremediation of heavy metal contaminated areas.     

Molecular identification of arbuscular mycorrhizal fungal spores associated to the rhizosphere of Retama raetam in Tunisia

ABSTRACT

Arbuscular mycorrhizal fungi (AMF) are found in the soil of most ecosystems where they form mutualistic associations that affect plants growth. We have investigated the community structure of AMF associated to Retama raetam growing in five regions of Tunisia. The total number of spores was significantly different across sites, ranging from 633 to 1062 spores per 100 g dry soil. A dominance of small spores was revealed. The large subunit region of the rDNA of AMF spores associated to the rhizosphere of R. raetam was sequenced. Sequences clustered into 13 operational taxonomic units. Phylogenetic analysis revealed that the majority of sequences were grouped within Glomeraceae and Claroideoglomeraceae families. Only two sequences were affiliated to the Scutellospora genus. These results suggest the dominance of the genus Glomus in the soil rhizosphere of R. raetam. A correlation between phylogenetic analysis, soil chemicals properties, and AMF community richness was also detected.     

Switch of tropical Amazon forest to pasture affects taxonomic composition but not species abundance and diversity of arbuscular mycorrhizal fungal community

Arbuscular mycorrhizal fungi (AMF) community composition and species richness are affected by several factors including soil attributes and plant host. In this paper we tested the hypothesis that conversion of tropical Amazon forest to pasture changes taxonomic composition of AMF community but not community species abundance and richness. Soil samples were obtained in 300 m × 300 m plots from forest (n = 11) and pasture (n = 13) and fungal spores extracted, counted and identified. A total of 36 species were recovered from both systems, with 83% of them pertaining to Acaulosporaceae and Glomeraceae. Only 12 species were shared between systems and spore abundance of the majority of fungal species did not differ between pasture and forest. Spore abundance was significantly higher in pasture compared to forest but both systems did not differ on mean species richness, Shannon diversity and Pielou equitability. Species abundance distribution depicted by species rank log abundance plots was not statistically different between both systems. We concluded that conversion of pristine tropical forest to pasture influences the taxonomic composition of AMF communities while not affecting species richness and abundance distribution.     

Arbuscular mycorrhizal fungal communities in changing environments: The effects of seasonality and anthropogenic disturbance in a seasonal dry forest

The landscape of Mexican seasonal dry forests is affected by various periodic (long and drastic drought) and random (elimination of the forest coverage for agricultural purposes) disturbance events. The community of arbuscular mycorrhizal fungi (AMF) responds to these changes, sporulating and reducing its activity during the dry season, and slowly reestablishing itself following abandonment of cultivated fields. To determine the dynamics of the AMF community in response to natural phenomena and anthropogenic disturbances, we collected soil samples during the wet and dry seasons from plots with different time periods since abandonment of agricultural activity, categorized as early (less than 5 years), middle (11–23 years), and late (over 30 years) age plots. From each plot, AMF spores were isolated and identified in order to estimate abundance, richness and diversity. In addition, the number of infective propagules and value of mycorrhizal inoculum potential were calculated for each plot. Twenty-three species were recorded, for which Glomeraceae and Acaulosporaceae were the most commonly represented families. Significant differences were found in AMF species richness among plots and seasons and the diversity index of AMF was higher than 1.0 in most cases. There were no significant differences in spore abundance. Viable propagules were observed in all soil samples, with fluctuations relating mainly to time since abandonment. Overall, seasonality has a strong influence on AMF diversity but not on AMF infectivity, while time since abandonment had a more important impact.     

Arbuscular mycorrhizal fungi diversity associated with two halophytes Lycium barbarum L. and Elaeagnus angustifolia L. in Ningxia,China

The Arbuscular mycorrhizal fungi (AMF) community in saline soils of Ningxia, China, was rarely reported. Soils in the rhizosphere of two important food plants, Lycium barbarum L. (Goji) and Elaeagnus angustifolia L. (Oleaster), were sampled from Ningxia (Goji from Huinong, HNGQ; Goji from Yinchuan, YCGQ; Oleaster from Yinchuan, YCSZ) to investigate the AMF community. Thirty-three AMF species from 11 genera were identified in total. The dominant family and genera were Glomeraceae, Acaulospora and Glomus, respectively. Septoglomus constrictum was the most abundant species. The AMF community composition of Goji was different from that of Oleaster (R = 0.26, p < 0.05), while the AMF community from Huinong differed from Yinchuan (R = 1.0, p = 0.01). These findings suggest a high AMF diversity in Ningxia saline soils and the effect of host plant identity on AMF community composition. Furthermore, the AMF diversity index positively correlated with available potassium (AK), available phosphorus (AP), available nitrogen (AN) and organic matter (OM), but negatively correlated with electric conductivity (EC). This result demonstrated that a high level of salinity might reduce soil fertility and AMF diversity. The saline area with high diversity of the AMF community in Ningxia is promising for screening AMF isolates for utilization in crop production.     

Fungal community composition in sodic soils subjected to long-term rice cultivation

ABSTRACT

Rice cultivation is widely used to improve saline-sodic soils in Northeast China. However, the chronological effect of rice cultivation on soil fungal communities has not been studied. Therefore, this study investigated the variation of soil fungal communities in different rice cultivation years. Compared with the blank area, the rice cultivation for 20 years significantly decreased the pH and electrical conductivity by 16.6% and 70.1%, while significantly increased the soil organic carbon and available phosphorus by 90.6% and 17.4 times, respectively. Meanwhile, the relative abundance of Ascomycota and Basidiomycota significantly decreased and increased after rice cultivation, respectively. Moreover, some genera of arbuscular mycorrhizal fungi (AMF), e.g. Corymbiglomus, Glomus, and Rhizophagus, and pathogenic fungi (Thanatephorus cucumeris) disappeared, while Dentiscutata (one genus of AMF) appeared after rice cultivation. In addition, the fungal richness significantly increased when the rice cultivation less than 15 years and the fungal communities were similar between 15 and 20 years. Our findings showed that rice cultivation improved the nutrient availability and reduced salinity-alkalinity stress of sodic soils. After the rice cultivation for 15 years, the soil fungal community tended to be stable.     

Effects of different management practices on arbuscular mycorrhizal fungal diversity in maize fields by a molecular approach

As obligate mutualistic symbionts, arbuscular mycorrhizal fungi (AMF) colonize the roots of many agricultural crops, and it is often claimed that agricultural practices are detrimental to AMF. As a result, agroecosystems impoverished in AMF may not get the fully expected range of benefits from these fungi. Using molecular markers on DNA extracted directly from soil and roots, we studied the effects of different management practices (tillage and N fertilization) on the AMF communities colonizing an experimental maize field in Central Italy. Our molecular analysis based on three different nuclear rRNA regions (18S, 28S and ITS) allowed us to assess AMF biodiversity. Glomeraceae members were the main colonizer, and they co-occurred with Gigasporaceae and Paraglomus regardless of the management practices applied. Diversisporaceae and Entrophosporaceae members were instead detected in the N-fertilized soils and in the untreated soil, respectively. The results obtained indicated that the general AMF assemblages structure and composition in the maize field plots appear to be primarily influenced by N fertilization and, to a lesser extent, by tillage. This study also validates the usefulness of multiple molecular markers to consolidate and refine the assessment of the environmental AMF diversity.     

Effect of winter wheat cover cropping with no-till cultivation on the community structure of arbuscular mycorrhizal fungi colonizing the subsequent soybean

Winter cover crops increase the amount of indigenous arbuscular mycorrhizal fungi (AMF) in the soil, providing beneficial effects such as enhancement of phosphorus uptake by the subsequent crop. However, its impact on the AMF community structure is not well understood. In the present study, we aimed to reveal the effect of winter wheat cover cropping with no-till cultivation on the AMF community structures in soil and roots of the subsequent soybean. For this purpose, we conducted a field experiment consisting of two treatments, no-till soybean cultivation after winter wheat cover cropping (NTWC) and conventional soybean cultivation after winter fallow management as a control (CONT). At the flowering stage of soybean, higher AMF colonization of soybean roots was observed in the NTWC plots compared with the CONT plots. Additionally, aboveground biomass and phosphorus uptake of soybean in the NTWC plots were significantly higher than those in the CONT plots. Molecular community analyses based on PCR-denaturing gradient gel electrophoresis (DGGE) of AMF 18S rRNA genes indicated that the AMF community structures in the soil and soybean root of the NTWC plots were clearly different from those of the CONT plots. The DGGE profiles showed that the wheat cover cropping preferentially increased some phylotypes belonging to Glomeraceae and Claroideoglomeraceae. In addition, most of the phylotypes were characteristically observed in the subsequent soybean root of the NTWC plots, strongly suggesting that these phylotypes colonizing the cover crop wheat were taken over by the subsequent soybean. Our study revealed the significant effect of winter cover cropping with no-till cultivation on the structure of AMF community colonizing the subsequent soybean.     

Effects of microplastic polystyrene, simulated acid rain and arbuscular mycorrhizal fungi on Trifolium repens growth and soil microbial community composition

Microplastic pollution is a global and ubiquitous environmental problem in the oceans as well as in the terrestrial environment. We examined the fate of microplastic polystyrene (MPS) beads in experimental soil in the presence and absence of symbiotic arbuscular mycorrhizal fungi (AMF) and simulated acid rain (SAR) to determine whether the combinations of these three factors altered the growth of white clover Trifolium repens. We found that MPS, SAR, or AMF added singly to soil did not alter T. repens growth or yields. In contrast, MPS and AMF together significantly reduced shoot biomass, while SAR and MPS together significantly reduced soil available phosphorus independent of AMF presence. Microplastic polystyrene, AMF, and SAR together significantly reduced soil NO^-₃-N. Arbuscular mycorrhizal fungi added singly also enriched the beneficial soil bacteria (genus Solirubrobacter), while MPS combined with AMF significantly enriched the potential plant pathogenic fungus Spiromastix. Arbuscular mycorrhizal fungi inoculation with MPS increased the abundance of soil hydrocarbon degraders independent of the presence of SAR. In addition, the abundance of soil nitrate reducers was increased by MPS, especially in the presence of AMF and SAR. Moreover, SAR alone increased the abundance of soil pathogens within the fungal community including antibiotic producers. These findings indicate that the coexistence of MPS, SAR, and AMF may exacerbate the adverse effects of MPS on soil and plant health.     

Nitrogen and phosphorus fertilization leads to soil arbuscular mycorrhizal fungal diversity changes and rainfed crop yield increase on the Loess Plateau of China: A 37-year study

More than 80% of plants form mutualistic symbiotic relationships with arbuscular mycorrhizal fungi (AMF), and the application of fertilizers, such as nitrogen (N) and phosphorus (P) fertilizers, is a common agricultural management practice to improve crop yield and quality. However, the potential effects of long-term N and P fertilization on the AMF community in the rainfed agricultural system of the Loess Plateau of China are still not well understood. In this study, a long-term field experiment was conducted based on orthogonal design, with three N levels (0, 90, and 180 kg ha^-1 year^-1) and three P levels (0, 90, and 180 kg ha^-1 year^-1) for wheat fertilization. Changes in AMF community and correlations between AMF community composition, soil environmental factors, and wheat yield component traits were analyzed using traditional biochemical methods and high-throughput sequencing technology. The results showed that long-term N and P addition had a significant effect on the AMF community structure and composition. Nitrogen application alone significantly reduced the richness and diversity of AMF community, whereas the combined application of N and P significantly increased the richness and diversity of AMF community. The AMF community was driven mainly by soil available P, total P, and pH. There was a significant positive correlation between Glomus abundance and wheat yield and a significant negative correlation between Paraglomus abundance and wheat yield. Long-term N and P addition directly increased crop yield and affected yield indirectly by influencing soil chemical properties and the AMF community. Combined application of N and P both at 90 kg ha^-1 year^-1 could improve the ecological and physiological functions of the AMF community and benefit the sustainable development of rainfed agriculture.     

Host plant benefit from association with arbuscular mycorrhizal fungi: variation due to differences in size of mycelium

Plants differ in the benefit they receive from an association with arbuscular mycorrhizal fungi (AMF) but it is unclear what factors determine host response. We tested whether this difference is due in part to differences among AMF families (Glomaceae, Gigasporaceae, and Acaulosporaceae) in the size of their mycelium. For example, an AMF with a large mycelium might be better able to transfer nutrients to its host. Alternatively, the large mycelium might present a large carbon drain for the host. It might also be the location of AMF mycelium that is important: whether it occurs in the root or in the soil. In a greenhouse experiment, four different host plant species were inoculated with each of 21 AMF isolates representing different mycelial sizes and we measured both host plant biomass and foliar phosphorus concentration over 12 weeks. AMF family significantly affected host biomass with larger internal mycelia conferring greater host benefit. However, both intra-family variation in AMF effect and host identity also influenced host response. For foliar P, AMF family did not affect host response significantly. Our results show that differences in mycelial size among AMF families may contribute to variation in host responsiveness to AMF, but other factors are also important.     

Intensive management enhances mycorrhizal respiration but decreases free-living microbial respiration by affecting microbial abundance and community structure in Moso bamboo forest soils

Intensive management is known to markedly alter soil carbon (C) storage and turnover in Moso bamboo forests compared with extensive management. However, the effects of intensive management on soil respiration (R_S) components remain unclear. This study aimed to evaluate the changes in different R_S components (root, mycorrhizal, and free-living microorganism respiration) in Moso bamboo forests under extensive and intensive management practices. A 1-year in-situ microcosm experiment was conducted to quantify the R_S components in Moso bamboo forests under the two management practices using mesh screens of varying sizes. The results showed that the total R_S and its components exhibited similar seasonal variability between the two management practices. Compared with extensive management, intensive management significantly increased cumulative respiration from mycorrhizal fungi by 36.73%, while decreased cumulative respiration from free-living soil microorganisms by 8.97%. Moreover, the abundance of arbuscular mycorrhizal fungi (AMF) increased by 43.38%, but bacterial and fungal abundances decreased by 21.65% and 33.30%, respectively, under intensive management. Both management practices significantly changed the bacterial community composition, which could be mainly explained by soil pH and available potassium. Mycorrhizal fungi and intensive management affected the interrelationships between bacterial members. Structural equation modeling indicated that intensive management changed the cumulative R_S by elevating AMF abundance and lowering bacterial abundance. We concluded that intensive management reduced the microbial respiration-derived C loss, but increased mycorrhizal respiration-derived C loss.     

巴西大西洋森林中巴西松地面根部显示丛枝菌根真菌高定殖率和多样性

Almost 30 different arbuscularmycorrhizal fungi (AMF)species, distributed in different genera such as Glomus, Acaulospora,Scutellospora,Entrophospora,Ambispora,Kuklospora,Gigaspora,and Archeospora, have been identified in the root zone of Araucaria angustifolia, known as Brazil Pine. During our AMF survey in this ecosystem, our attention was called to the presence of many superficially growing Araucaria roots. Our hypothesis was that these roots were colonized with AMF because of the presence of AMF spores in organic material aboveground. Samples of these superficial roots and the organic substrate they were growing on were evaluated for their mycorrhizal status. DNA was extracted from the AMF colonized superficial roots and submitted to polymerase chain reaction (PCR) amplification using the NS31-AM1 primer pair, followed by cloning and sequencing. We found that the root colonization percentages were between 31% and 52%, and the number of AMF spores in the substrate ranged from 27 to 164 spores per 50 g dry substrate.The phylogenetic analyses and tree construction using maximum parsimony (MP) and neighbor-joining (NJ) methods identified 13 different species of the phylum Glomeromycota belonging to the genera Glomus, Funneliformis, Rhizophagus, Gigaspora, Acaulospora,and Archaeospora, and five isolates were identified only at the genus level. To our knowledge, this is the first report on Araucaria angustifolia with roots growing aboveground, producing runner roots that develop on dead tree trunks and organic material. The higher colonization of the aboveground roots than those commonly found in belowground Araucaria roots suggests that they may present active metabolic uptakeof nutrients.     

Assessing Genetic Diversity of Chinese Cultivated Barley by STS Markers

To assess the genetic diversity among China’s cultivated barley, sequence tagged site (STS) marker analysis was carried out to characterize 109 morphologically distinctive accessions originating from five Chinese eco-geographical zones. Fourteen polymorphic STS markers representing at least one in each chromosome were chosen for the analysis. The 14 STS markers revealed a total of 47 alleles, with an average of 3.36 alleles per locus (range 2–8). The proportion of polymorphic loci per population averaged 0.84 (range 0.71–1.00); the mean gene diversity averaged 0.39 (range 0.28–0.49). The means of P and H_e were highest in the Yangtze reaches and Southern zone (P = 1.00; H_e = 0.46) and lowest (P = 0.71 He = 0.28) in the Yellow river reaches zone. The STS diversity in different zones is quite different from the morphology diversity. The STS variation was partitioned into 17% among the zone and 83% within the zone. Both cluster and principal coordinate analyses clearly separated the accessions into a dispersed group (mostly two-rowed barley with a lower mean GS value) and a concentrated group (mostly six-rowed barley with a higher mean GS value) according to the spike characteristic with only a few exceptions. The accessions from the Qinghai-Tibet plateau formed a distinctive subgroup and can be distinguished from the concentrated group. The role of Tibet in the origin and evolution of cultivated barley has been discussed.     

Effects of interactions between arbuscular mycorrhizal fungi and bacteria on the growth of Lotus corniculatus L.: From the perspective of regulating rhizosphere fungal community

Arbuscular mycorrhizal fungi (AMF) provide essential nutrients to crops and are affected by fertilizers. Phosphate-solubilizing bacteria (PSB), nitrogen-fixing bacteria (NFB), and AMF have mutually beneficial relationships with plants, but the effects of their interactions on plant growth by regulating rhizosphere fungal community have not been sufficiently studied. In this study, a greenhouse pot experiment was conducted to investigate the interactions between AMF and bacteria (PSB and NFB) on the growth of Lotus corniculatus L. Specifically, the role of rhizosphere fungal community in the growth of Lotus corniculatus L. was explored using Illumina MiSeq high-throughput sequencing. The results showed that combined inoculation of AMF with PSB and NFB increased plant biomass, plant height, and fungal colonization rate. The richness, complexity, and stability of rhizosphere fungal community also increased after combined inoculation of AMF with PSB and/or NFB, particularly with PSB. In addition, combined inoculation of AMF with PSB and NFB enriched the abundance of beneficial microorganisms, with Chaetomium and Humicola showing the greatest alterations. The structural equation model showed that the interactions of AMF with PSB and NFB promoted plant growth by affecting fungal network structure and soil enzyme activities involved in carbon, nitrogen, and phosphorus cycling. These findings provide evidence for the effects of interactions of AMF with PSB and NFB on rhizosphere fungal community and plant growth.     

长期保护性耕作对丛枝菌根真菌多样性的影响

为了明确我国北方干旱地区长期保护性耕作以及深松对丛枝菌根真菌(AMF)多样性的影响,笔者于2014年在山西省临汾市连续22年实施保护性耕作的长期定位试验基地,针对免耕覆盖(NTS)、深松免耕覆盖(SNTS)及传统耕作(TT)3种处理方式,进行了不同耕作条件下土壤AMF物种丰度、孢子密度、Shannon多样性指数以及AMF侵染率等因素的比较研究。结果显示,长期保护性耕作(NTS和SNTS)共分离鉴定出AMF 7属9种,其中根孢囊霉属(Rhizophagus)和斗管囊霉属(Funneliformis)各2种,球囊霉属(Glomus)、近明球囊霉属(Claroideoglomus)、无梗囊霉属(Acaulospora)、硬囊霉属(Sclerocystis)和隔球囊霉属(Septoglomus)各1种;而传统耕作(TT)共分离鉴定出AMF 6属8种,没有检测到无梗囊霉属。NTS、SNTS和TT处理在不同土层的AMF优势种基本一致,0~40 cm土层为摩西斗管囊霉(Fu.mosseae)和变形球囊霉(G.versiforme),40~80 cm土层为摩西斗管囊霉、变形球囊霉和聚丛根孢囊霉(Rh.aggregatum),80~120 cm土层为聚丛根孢囊霉,120 cm土层以下只有NTS和SNTS处理中存在聚丛根孢囊霉,说明保护性耕作措施促进了AMF向土壤深层发展。NTS和SNTS处理在同一土层的AMF物种丰度、孢子密度和Shannon多样性指数均高于TT处理,SNTS处理高于NTS处理。同一耕作措施不同土层的AMF物种丰度、孢子密度和Shannon多样性指数均随土层加深而逐渐降低;NTS和SNTS处理在小麦各生育期的丛枝侵染率和孢子密度均高于TT处理;各处理在小麦拔节期的AMF侵染率最高,分别为14.9%、16.1%和10.6%,而在收获期的土壤孢子密度最高,分别为111.7个·(100g)~(-1)、125.0个·(100g)~(-1)和90.3个·(100g)~(-1)。研究认为,长期免耕覆盖、尤其深松免耕覆盖,提高了AMF多样性。该研究结果可为中国北方旱作农田生态系统中AMF自然潜力的充分发挥,以及保护性耕作技术的合理应用提供科学依据。     

Effect of agricultural management practices on arbuscular mycorrhizal fungal abundance in low-input cropping systems of southern Africa: a case study from Zimbabwe

Previous research, mostly in temperate agricultural systems, has shown that management practices such as fallow period, tillage, crop rotation, and phosphorus (P) fertilizer applications can influence the abundance of arbuscular mycorrhizal fungi (AMF), but relatively little is known about their effect in smallholder farmers’ fields in sub-Saharan Africa. In this study, we evaluated the effect of four subsistence crops that form associations with AMF, moderate P fertilization, tillage, and fallow period on the subsequent AMF abundance on three contrasting low fertility soils in south-western Zimbabwe. Arbuscular mycorrhizal fungal abundance was estimated based on early mycorrhizal colonization of maize (Zea mays L.) or lablab (Lablab purpureus L.) following the various treatments. The previously grown crop significantly affected AMF abundance (p < 0.001). It was highest after lablab followed by pigeonpea (Cajanus cajan L.), maize, and groundnut (Arachis hypogaea L.), and there were significant positive correlations between AMF abundance and aboveground biomass of pigeonpea, lablab, and maize. Contrary to much previous research, P fertilization, fallowing, and tillage did not significantly decrease AMF abundance. In smallholder farmers’ fields in the semi-arid tropics of sub-Saharan Africa, therefore, growing vigorous mycorrhizal plants prior to the dry season could be more important than minimizing P fertilizer applications, fallow periods, and tillage to maintain or increase AMF abundance.     

Impact of 12-year field treatments with organic and inorganic fertilizers on crop productivity and mycorrhizal community structure

The effect of manure and mineral fertilization on the arbuscular mycorrhizal (AM) fungal community structure of sunflower (Helianthus annuus L.) plants was studied. Soils were collected from a field experiment treated for 12 years with equivalent nitrogen (N) doses of inorganic N, dairy manure slurry, or without N fertilization. Fresh roots of tall fescue (Festuca arundinacea Schreb.) grass collected from the field plots without N fertilization and unfumigated field soils were used as native microbial inoculum sources. Sunflower plants were sown in pots containing these soils, and three different means of manipulating the microbial community were set: unfumigated soil with fresh grass roots, fumigated soil with fresh grass roots, or fumigated soil with sterilized grass roots. Assessing the implications with respect to plant productivity and mycorrhizal community structure was investigated. Twelve AM fungal OTUs were identified from root or soil samples as different taxa of Acaulospora, Claroideoglomus, Funneliformis, Rhizophagus, and uncultured Glomus, using PCR-DGGE and sequencing of an 18S rRNA gene fragment. Sunflower plants grown in manure-fertilized soils had a distinct AMF community structure from plants either fertilized with mineral N or unfertilized, with an abundance of Rhizophagus intraradices-like (B2). The results also showed that AM inoculation increased P and N contents in inorganic N-fertilized or unfertilized plants, but not in manure-fertilized plants.     

Impact of a 5-year winter cover crop rotational system on the molecular diversity of arbuscular mycorrhizal fungi colonizing roots of subsequent soybean

The impact of winter cover crops, specifically wheat (Triticum aestivum L.), red clover (Trifolium pratense L.), and rapeseed (Brassica napus L.) or winter fallow, on community composition of arbuscular mycorrhizal fungi (AMF) in subsequent soybean roots was investigated in a 5-year field trial on andosolic soils in Japan. Soybean roots were sampled at full-flowering and analyzed for AMF communities using a partial LSU rDNA region. Phylogenetic analysis detected 22 AMF phylotypes, including eight Glomus, three Gigaspora, two Scutellospora, three Acaulospora, two Rhizophagus, and one of Funneliformis, Diversispora, Paraglomus, and an unknown glomeromycete in the roots. The 5-year rotation of different winter cover crops or winter fallow did not impact the molecular diversity of AMF communities colonizing the roots of subsequent soybean. In all of the rotations, Glomus and Gigaspora phylotypes were common to soybean roots over the 5-year period. Redundancy analysis (RDA) demonstrated that AMF communities in the roots of subsequent soybean were not significantly different among winter cover crop rotations or fallow. However, AMF communities in soybean roots were clearly influenced by rotation year suggesting that climate or other environmental factors were more important than winter cover cropping system management.     

Varied rates of mycorrhizal inoculum on growth and nutrient acquisition by barley grown with drought stress

Effectiveness of arbuscular mycorrhizal fungi (AMF) is crucial for maximum plant growth and acquisition of mineral nutrients under drought. The objective of this research was to determine effects of varied rates of AMF inoculum on plant growth and acquisition of phosphorus (P), zinc (Zn), copper (Cu), and manganese (Mn) by barley (Hordeum vulgare L. cv. SLB‐6) grown with and without drought stress (WS and nonWS). Plants inoculated with four inoculum rates [control (M₀), 120 (M₁), 240 (M₂), and360 (M₃) spores per 100 g dry soil] of Glomus mosseae were grown in a low P silty clay (Typic Xerochrept) soil (pH=8.0) mix in a greenhouse for 45 days. Root AMF colonization increased as inoculum rate increased in plants grown with WS and nonWS. Leaf area and shoot and root dry matter (DM) increased as inoculum rate increased up to M₂ regardless of soil moisture. Shoot concentrations of P, Cu, and Mn were generally higher for mycorrhizal (AMF) than for nonmycorrhizal (nonAMF) plants grown with both WS and nonWS. Shoot contents of P, Zn, Cu, and Mn were higher for AMF than for nonAMF plants grown with nonWS, and shoot contents of P were higher for AMF than for nonAMF plants with WS. For plants grown with WS and nonWS, contents of P, Zn, Cu, and Mn were generally higher for plants inoculated with M₂ compared to other rates of inoculum. The results of this study indicated that plant responses to root colonization with AMF were dependent on AMF rate and soil moisture. Based on enhancements in plant DM and mineral acquisition traits, M₂ inoculum was the most effective rate of inoculation for this AMF isolate.