Host Arbuscular Mycorrhizal Fungi Research Articles

Spores of arbuscular mycorrhizal fungi host surprisingly diverse communities of endobacteria.

Arbuscular mycorrhizal fungi (AMF) are ubiquitous plant root symbionts, which can house two endobacteria: Ca. Moeniiplasma glomeromycotorum (CaMg) and Ca. Glomeribacter gigasporarum (CaGg). However, little is known about their distribution and population structure in natural AMF populations and whether AMF can harbour other endobacteria. We isolated AMF from two environments and conducted detailed analyses of endobacterial communities associated with surface-sterilised AMF spores. Consistent with the previous reports, we found that CaMg were extremely abundant (80%) and CaGg were extremely rare (2%) in both environments. Unexpectedly, we discovered an additional and previously unknown level of bacterial diversity within AMF spores, which extended beyond the known endosymbionts, with bacteria belonging to 10 other phyla detected across our spore data set. Detailed analysis revealed that: CaGg were not limited in distribution to the Gigasporaceaefamily of AMF, as previously thought; CaMg population structure was driven by AMF host genotype; and a significant inverse correlation existed between the diversity of CaMg and diversity of all other endobacteria. Based on these data, we generate novel testable hypotheses regarding the function of CaMg in AMF biology by proposing that they might act as conditional mutualists of AMF.

Soil Physicochemical Characteristics and Spore Density of Indigenous Arbuscular Mycorrhizal Fungi (AMF) in Different Vegetation Patches of a Marginal Upland in Central Philippines

To show the importance of plant-microbe association in stressed tropical landscapes, the study evaluated the physicochemical characteristics and indigenous arbuscular mycorrhizal fungi (AMF) spore density in selected vegetation patches of marginal upland soils in Central Philippines. Five quadrats were used in the study, namely Andropogon aciculatus (control plot), Imperata cylindrica, Chromolaena odorata, Melastoma malabathricum and mixed vegetation patch. Results showed that soils in the studied vegetation patches had different physicochemical characteristics and AMF spore density. Although all patches had clay soil texture and comparable water-holding capacity, mixed vegetation patch had moderate compaction (1.33 g cm-3) and higher porosity (50.31%) compared with the other patches, which had extreme compaction (1.37-1.65 g cm-3) and lower porosity (37.74-48.76%). In terms of chemical properties, soils in different patches had moderate (5.69) to strongly acidic pH (5.13), moderate organic matter (2.69-2.91%) levels, low P (2.67-3.94 ppm) content and above critical K levels (0.2-1.2 cmol+ kg-1). Results also revealed that C. odorata patch had the highest spore density count (11.33 spores 100 g-1), followed by mixed vegetation (9 spores 100 g-1), M. malabathricum (8.33 spores 100 g-1), and A. aciculatus patch having the lowest spore density count (4 spores 100 g-1). The significant spore density variability was attributed to the differences in soil’s physicochemical characteristics among the different vegetation patches and AMF host specificity. Spores detection, therefore, indicated AMF presence and helped the adaptation mechanism of the natural vegetation in this degraded upland.

Different Arbuscular Mycorrhizal Fungi Established by Two Inoculation Methods Improve Growth and Drought Resistance of Cinnamomum Migao Seedlings Differently.

Simple SummaryDrought is a global climatic phenomenon and one of the main factors that negatively affect plant growth. Karst is a unique type of ecosystem where ecological degradation is becoming more and more serious due to the aggravation of global drought. Vegetation restoration is an effective method for preventing ecological degradation in Karst ecosystems. Cinnamomum migao is selected as the tree species for vegetation restoration, because it is a unique, fast-growing medicinal plant of Southwest China that only thrives in Karst regions. Arbuscular mycorrhizal fungi (AMF) are an important component of the soil biota in ecosystems and alleviate drought stress in plants by forming a mutualistic symbiosis. Most previous studies just considered the effects of AMF species on drought resistance but did not evaluate different inoculation methods. The aim of the present study was to compare the effects of different AMF resulting from the use of different inoculation methods on the growth and drought resistance of C. migao seedlings in Karst soil. The findings of this study will improve the success rate of reforestation programs in Karst ecosystems through the utilization of these important microorganisms.Drought stress is one of the greatest obstacles affecting field crop productivity in arid and semi-arid regions, and its severity and frequency are expected to increase due to human-induced changes to the environment and climate. Drought has led to rocky desertification in Karst regions. Cinnamomum migao is a unique, fast-growing medicinal plant of Southwest China that only thrives in Karst regions. Arbuscular mycorrhizal fungi (AMF) symbiosis alleviates drought stress in plants; however, establishment and function of the symbiotic interaction between AMF host plant in relation to the inoculation method remain unclear. Therefore, we conducted an experiment to investigate the effects of AMF species (Glomus etunicatum and Funneliformis mosseae) and two inoculation methods (seed vs. seedling inoculation) under drought stress on C. migao seedlings, and quantified mycorrhizal colonization, AMF spore density, root vigor, relative water content, C. migao growth, antioxidant enzyme activities, and osmotic adjustment. Inoculation with AMF (G. etunicatum and F. mosseae) positively affected the growth and root vigor of Cinnamomum migao under drought stress, regardless of the inoculation method. Additionally, both AMF species markedly upregulated antioxidant enzyme activities and osmotic adjustment substances, regardless of the inoculation method. Our results showed that the collective stimulatory effect of G. etunicatum is more efficient than that of F. mosseae. AMF application could promote afforestation with C. migao to prevent rocky desertification in Karst regions where water is the greatest limiting factor on plant growth and yield.

Boreal soil microbial diversity and seed onion mycorrhizal colonization is unaffected by preceding one season crop cultivation

Arbuscular mycorrhizal fungi (AMF) enhance plant phosphorus uptake, increase soil water holding abilities, reduce soil erosion and can protect their hosts from soil-borne pathogens. Hence, AMF play an important part in improving sustainable agricultural practices, and information about the effects of different preceding crop species on the following crop's AMF well-being is crucial for designing crop rotations.We studied onion root and soil microbial diversity and onion root AMF colonization rates after being preceded by three AMF hosting and one non-hosting green manure crop species in a boreal climate organic field.One-season cultivation of different preceding green manure crops did not have a strong effect on AMF colonization or microbial diversity in onion roots nor in the surrounding soil. Onions had high AMF colonization and microbial diversity after all four preceding crops. The overall fungal and bacterial populations of the soil reacted more strongly to seasonal variations than preceding crops.The study suggests that one season is a too short time to influence the AMF community in boreal climate organic fields with conventional tillage. Thus, non-host preceding crops can also be used in rotations, especially together with AMF host crops.

AMF enhance secondary metabolite production in ashwagandha, licorice, and marigold in a fungi-host specific manner

Strategies to enhance the production of secondary metabolites, derived from medicinal and agriculturally important plants have been the subject of exploration to enable effective utilization of these biorepositories. Through symbiosis, arbuscular mycorrhizal fungi (AMF), modify plant primary and secondary metabolite biosynthesis. The relationship thus offers the opportunity to exploit combinations of host and fungus that maximize secondary metabolite production. We investigated different AMF host combinations for the enhancement of root-derived secondary metabolites from three plant species - ashwagandha (Withania somnifera (L.) Dunal), licorice (Glycyrrhiza glabra L.), and marigold (Tagetes erecta L.). Each host species was inoculated singly with each of five species of AMF, Glomus hoi, Claroideoglomus etunicatum, Claroideoglomus claroideum, Rhizophagus irregularis, and Acaulospora delicata and secondary metabolite production was assessed. Increased concentrations of the following secondary metabolites were found in roots after AMF establishment: for withaferin-A in ashwagandha (concentrations ranged from 11.5 to 43.5% above than in control non-mycorrhized roots depending on the host and AMF combination); in licorice, glycyrrhizic acid (1.51–3.92% above control) and glabridin (2.85–6.41% above control) and in marigold, alpha-terthienyl (1.51–7.18% above control). Specifically, among the AMF inoculations, the highest levels of secondary metabolite were found in ashwagandha and marigold inoculated with R. irregularis and for licorice following inoculation with C. etunicatum revealing the impact of different AMF species on different plant species. This underpinning knowledge of AMF symbioses with the plant host will augment the development of methods that will provide enhanced concentrations of secondary metabolites of commercial value.

Gigaspora margarita and Its Endobacterium Modulate Symbiotic Marker Genes in Tomato Roots under Combined Water and Nutrient Stress.

As members of the plant microbiota, arbuscular mycorrhizal fungi (AMF) may be effective in enhancing plant resilience to drought, one of the major limiting factors threatening crop productivity. AMF host their own microbiota and previous data demonstrated that endobacteria thriving in Gigaspora margarita modulate fungal antioxidant responses. Here, we used the G. margarita–Candidatus Glomeribacter gigasporarum system to test whether the tripartite interaction between tomato, G. margarita and its endobacteria may improve plant resilience to combined water/nutrient stress. Tomato plants were inoculated with spores containing endobacteria (B+) or not (B-), and exposed to combined water/nutrient stress. Plants traits, AM colonization and expression of AM marker genes were measured. Results showed that mycorrhizal frequency was low and no growth effect was observed. Under control conditions, B+ inoculated plants were more responsive to the symbiosis, as they showed an up-regulation of three AM marker genes involved in phosphate and lipids metabolism compared with B− inoculated or not-inoculated plants. When combined stress was imposed, the difference between fungal strains was still evident for one marker gene. These results indicate that the fungal endobacteria finely modulate plant metabolism, even in the absence of growth response.

Extensive membrane systems at the host-arbuscular mycorrhizal fungus interface.

During arbuscular mycorrhizal (AM) symbiosis, cells within the root cortex develop a matrix-filled apoplastic compartment in which differentiated AM fungal hyphae called arbuscules reside. Development of the compartment occurs rapidly, coincident with intracellular penetration and rapid branching of the fungal hypha, and it requires much of the plant cell's secretory machinery to generate the periarbuscular membrane that delimits the compartment. Despite recent advances, our understanding of the development of the periarbuscular membrane and the transfer of molecules across the symbiotic interface is limited. Here, using electron microscopy and tomography, we reveal that the periarbuscular matrix contains two types of membrane-bound compartments. We propose that one of these arises as a consequence of biogenesis of the periarbuscular membrane and may facilitate movement of molecules between symbiotic partners. Additionally, we show that the arbuscule contains massive arrays of membrane tubules located between the protoplast and the cell wall. We speculate that these tubules may provide the absorptive capacity needed for nutrient assimilation and possibly water absorption to enable rapid hyphal expansion.

The carbon economy of drought: comparing respiration responses of roots, mycorrhizal fungi, and free-living microbes to an extreme dry-rewet cycle

The effects of drying and wetting on soil carbon processes are regulated by the responses of plants, plant-associated microbes, and free-living microbes. Whether these groups respond similarly to drying and wetting is not clear, however, making it difficult to predict the net effect of drought on soil carbon processes. We imposed a drought-rewetting event on mesocosms planted with maple (Acer saccharum Marshall; arbuscular mycorrhizal fungi host) or oak (Quercus alba L.; ectomycorrhizal fungi host) saplings. In each mesocosm, we used mesh to create chambers separating roots, mycorrhizal fungi hyphae, and free-living microbes. We compared respiration and carbon degrading enzyme activity across chambers throughout the dry-rewetting cycle. Respiration from all chambers declined during drought, and chambers differed in their drought-sensitivity. In maple mesocosms, respiration from the Hyphae+Microbes chamber was the most drought-resistant; in oak mesocosms respiration from the Microbes chamber was the most drought-sensitive. Respiration did not recover after rewatering, indicating a persistent drought legacy. In contrast, enzyme activity returned to control functioning after 2 weeks of well-watered conditions. Our results suggest that belowground biota differ in their sensitivity to and recovery from drought, which affects the carbon processes differently. An improved ability to partition carbon fluxes into biotic sources can help to constrain predicted carbon fluxes under future climate scenarios.

A Novel Positive Regulator of the Early Stages of Root Nodule Symbiosis Identified by Phosphoproteomics.

Signals and signaling pathways underlying the symbiosis between legumes and rhizobia have been studied extensively over the past decades. In a previous phosphoproteomic study on the Medicago truncatula-Sinorhizobium meliloti symbiosis, we identified plant proteins that are differentially phosphorylated upon the perception of rhizobial signals, called Nod factors. In this study, we provide experimental evidence that one of these proteins, Early Phosphorylated Protein 1 (EPP1), is required for the initiation of this symbiosis. Upon inoculation with rhizobia, MtEPP1 expression was induced in curled root hairs. Down-regulation of MtEPP1 in M. truncatula roots almost abolished calcium spiking, reduced the expression of essential symbiosis-related genes (MtNIN, MtNF-YB1, MtERN1 and MtENOD40) and strongly decreased nodule development. Phylogenetic analyses revealed that orthologs of MtEPP1 are present in legumes and specifically in plant species able to host arbuscular mycorrhizal fungi, suggesting a possible role in this association too. Short chitin oligomers induced the phosphorylation of MtEPP1 like Nod factors. However, the down-regulation of MtEPP1 affected the colonization of M. truncatula roots by arbuscular mycorrhizal fungi only moderately. Altogether, these findings indicate that MtEPP1 is essential for the establishment of the legume-rhizobia symbiosis but might plays a limited role in the arbuscular mycorrhizal symbiosis.

Long‐term Soil Tillage and Cover Cropping Affected Arbuscular Mycorrhizal Fungi, Nutrient Concentrations, and Yield in Sunflower

Core Ideas Novel insights in the arbuscular mycorrhizal fungi tillage cover crop interaction based on a long term trial. Cover crops and soil tillage affect arbuscular mycorrhizal fungi colonization in the subsequent main crop. Nutrient concentrations and C/N ratio were affected by soil tillage. Reduction of soil tillage and whole‐year coverage are major factors for sustainable agriculture. Arbuscular mycorrhizal fungi (AMF) are major components of the native soil microbiome in agricultural soils. Soil tillage and cover cropping can play an important role in promoting AMF abundance. In the present study, the results of a field experiment comprising different soil tillage treatments (conventional, reduced, minimum, no‐tillage) in interaction with cover cropping (comprising AMF host and nonhost plants) in a common crop rotation with Triticum aestivum (winter wheat) and Helianthus annuus (sunflower) as the main crops are presented. Different cover crops (in mixtures or as single components) were cultivated in an existing soil tillage experiment established in 2009 in Austria. Soil tillage affected mycorrhization of winter wheat but not of cover crops. A different AMF root colonization were found in several cover crop species and in the subsequent sunflower. In this crop, AMF root colonization and spore density was further affected by soil tillage. The grain yields of the main crops were not altered by soil tillage. Significant interactions of soil tillage and cover cropping were found in the yield of sunflower and the C/N ratios. Furthermore, the nutrient concentrations of the plants were affected by soil tillage. This study shows that reduced soil tillage intensity combined with cover cropping enhances the abundance of AMF in the soil and affects the yield of the following main crop. Notably, mycorrhizal nonhost plants as cover crops do not lead to negative conditions for AMF in a common crop rotation.

Strong indirect herbicide effects on mycorrhizal associations through plant community shifts and secondary invasions.

Million of acres of U.S. wildlands are sprayed with herbicides to control invasive species, but relatively little is known about non-target effects of herbicide use. We combined greenhouse, field, and laboratory experiments involving the invasive forb spotted knapweed (Centaurea stoebe) and native bunchgrasses to assess direct and indirect effects of the forb-specific herbicide picloram on arbuscular mycorrhizal fungi (AMF), which are beneficial soil fungi that colonize most plants. Picloram had no effect on bunchgrass viability and their associated AMF in the greenhouse, but killed spotted knapweed and reduced AMF colonization of a subsequent host grown. Results were similar in the field where AMF abundance in bunchgrass-dominated plots was unaffected by herbicides one year after spraying based on 16:1ω5 phospholipid fatty acid (PLFA) and neutral lipid fatty acid (NLFA) concentrations. In spotted-knapweed-dominated plots, however, picloram application shifted dominance from spotted knapweed, a good AMF host, to bulbous bluegrass (Poa bulbosa), a poor AMF host. This coincided with a 63% reduction in soil 16:1ω5 NLFA concentrations but no reduction of 16:1ω5 PLFA. Because 16:1ω5 NLFA quantifies AMF storage lipids and 16:1ω5 PLFA occurs in AMF membrane lipids, we speculate that the herbicide-mediated reduction in host quality reduced fungal carbon storage, but not necessarily fungal abundance after one year in the field. Overall, in greenhouse and field experiments, AMF were only affected when picloram altered host quantity and quality. This apparent lack of direct effect was supported by our in-vitro trial where picloram applied to AMF mycelia did not reduce fungal biomass and viability. We show that the herbicide picloram can have profound, indirect effects on AMF within one year. Depending on herbicide-mediated shifts in host quality, rapid interventions may be necessary post herbicide applications to prevent loss of AMF abundance. Future research should assess consequences of these potential shifts for the restoration of native plants that differ in mycorrhizal dependency.

The endobacterium of an arbuscular mycorrhizal fungus modulates the expression of its toxin-antitoxin systems during the life cycle of its host.

Arbuscular mycorrhizal fungi (AMF) are widespread root symbionts that perform important ecological services, such as improving plant nutrient and water acquisition. Some AMF from the Gigasporaceae family host a population of endobacteria, Candidatus Glomeribacter gigasporarum (Cagg). The analysis of the Cagg genome identified six putative toxin-antitoxin modules (TAs), consisting of pairs of stable toxins and unstable antitoxins that affect diverse physiological functions. Sequence analysis suggested that these TA modules were acquired by horizontal transfer. Gene expression patterns of two TAs (yoeB/yefM and chpB/chpS) changed during the fungal life cycle, with the expression during the pre-symbiotic phase higher than during the symbiosis with the plant host. The heterologous expression in Escherichia coli demonstrated the functionality only for the YoeB-YefM pair. On the basis of these observations, we speculate that TA modules might help Cagg adapt to its intracellular habitat, coordinating its proliferation with the physiological state of the AMF host.

English

The aim of our work was to assess the effect of inoculation with three arbuscular mycorrhizal fungi (AMF) ( Rhizoglomus aggregatum (N.C. Schenck and G.S. Sm.) Sieverd., G.A. Silva and Oeh., Funneliformis mosseae (T.H. Nicolson and Gerd.) C. Walker and A. Schussler. and Rhizoglomus intraradices (N.C. Schenck and G.S. Sm.) Sieverd., G.A. Silva and Oehl.), and a mixed inoculum of these AMF on root colonization, biomass production, mycorrhizal dependency (MD) and shoot mineral contents of two salt tolerant grasses Leptochloa fusca L. Stapf and Sporobolus robusts Kunth. After four months of growth in a sterilized soil and greenhouse conditions, grasses inoculated with AMF showed significantly higher total biomass production than non-inoculated seedlings. MD and shoot mineral contents (especially P) varied with AMF host plants. Maximum values of MD (13%) were observed in L. fusca and S. robustus seedlings when inoculated with R. intraradices and F. mosseae , respectively. Only P contents were higher in the S. robustus /mixed-AMF combinations than the other treatments. These results demonstrate the potential benefits in our experimental conditions of AM inoculation for improving growth and P acquisition particularly in the L. fusca / F. mosseae and S. robustus /mixed-AMF combinations. Key words: Grass species, symbiosis, mycorrhizal dependency, mineral nutrition.

Mosaic genome of endobacteria in arbuscular mycorrhizal fungi: Transkingdom gene transfer in an ancient mycoplasma-fungus association

For more than 450 million years, arbuscular mycorrhizal fungi (AMF) have formed intimate, mutualistic symbioses with the vast majority of land plants and are major drivers in almost all terrestrial ecosystems. The obligate plant-symbiotic AMF host additional symbionts, so-called Mollicutes-related endobacteria (MRE). To uncover putative functional roles of these widespread but yet enigmatic MRE, we sequenced the genome of DhMRE living in the AMF Dentiscutata heterogama. Multilocus phylogenetic analyses showed that MRE form a previously unidentified lineage sister to the hominis group of Mycoplasma species. DhMRE possesses a strongly reduced metabolic capacity with 55% of the proteins having unknown function, which reflects unique adaptations to an intracellular lifestyle. We found evidence for transkingdom gene transfer between MRE and their AMF host. At least 27 annotated DhMRE proteins show similarities to nuclear-encoded proteins of the AMF Rhizophagus irregularis, which itself lacks MRE. Nuclear-encoded homologs could moreover be identified for another AMF, Gigaspora margarita, and surprisingly, also the non-AMF Mortierella verticillata. Our data indicate a possible origin of the MRE-fungus association in ancestors of the Glomeromycota and Mucoromycotina. The DhMRE genome encodes an arsenal of putative regulatory proteins with eukaryotic-like domains, some of them encoded in putative genomic islands. MRE are highly interesting candidates to study the evolution and interactions between an ancient, obligate endosymbiotic prokaryote with its obligate plant-symbiotic fungal host. Our data moreover may be used for further targeted searches for ancient effector-like proteins that may be key components in the regulation of the arbuscular mycorrhiza symbiosis.

Plant-driven genome selection of arbuscular mycorrhizal fungi.

Plant-driven genome selection of arbuscular mycorrhizal fungi.

Studies on AM associations in Marchantia nepalensis L. et L.

accessions of Marchantia nepalensis were studied for mycorrhizal invasion in the rhizoids and thallus. fungal hyphae/vesicles/arbuscules were recorded in all the samples. The fungal hyphae never colonized the sporophytic tissue. The fungal structures observed in M. nepalensis during the present study are similar to those reported for the plant host-arbuscular mycorrhizal fungus (AMF) interactions. Spores of seven species of Glomus have also been isolated from rhizosphere soils of M. nepalensis.

Detection of a novel intracellular microbiome hosted in arbuscular mycorrhizal fungi.

Arbuscular mycorrhizal fungi (AMF) are important members of the plant microbiome. They are obligate biotrophs that colonize the roots of most land plants and enhance host nutrient acquisition. Many AMF themselves harbor endobacteria in their hyphae and spores. Two types of endobacteria are known in Glomeromycota: rod-shaped Gram-negative Candidatus Glomeribacter gigasporarum, CaGg, limited in distribution to members of the Gigasporaceae family, and coccoid Mollicutes-related endobacteria, Mre, widely distributed across different lineages of AMF. The goal of the present study is to investigate the patterns of distribution and coexistence of the two endosymbionts, CaGg and Mre, in spore samples of several strains of Gigaspora margarita. Based on previous observations, we hypothesized that some AMF could host populations of both endobacteria. To test this hypothesis, we performed an extensive investigation of both endosymbionts in G. margarita spores sampled from Cameroonian soils as well as in the Japanese G. margarita MAFF520054 isolate using different approaches (molecular phylotyping, electron microscopy, fluorescence in situ hybridization and quantitative real-time PCR). We found that a single AMF host can harbour both types of endobacteria, with Mre population being more abundant, variable and prone to recombination than the CaGg one. Both endosymbionts seem to retain their genetic and lifestyle peculiarities regardless of whether they colonize the host alone or together. These findings show for the first time that fungi support an intracellular bacterial microbiome, in which distinct types of endobacteria coexist in a single cell.

Erosion or plant succession — How to interpret the presence of arbuscular mycorrhizal fungi (Glomeromycota) spores in pollen profiles collected from mires

The spores of arbuscular mycorrhizal fungi (AMF), microorganisms which occur belowground, are recognized as important indicators of erosion in palaeoecological reconstructions. In this study, the indicative value of the AMF was examined in peat deposits. A combination of palaeoecological methods, involving loss on ignition (LOI) and palynological analysis, and mycological techniques, including the assessment of AMF colonization of roots and AMF trap cultures, was used. A layer with abundant AMF spores parallel to other erosion indicators was thereby examined. The results clearly proved that the application of AMF spores as erosion indicators in peat deposits is highly questionable because the spores may have been produced by mycorrhizal mycelia related to AMF host plants whose roots have grown into the layer where the deposits lie. Nonetheless, AMF should still be considered as important markers of episodes of higher downwash in continuous lacustrine sediments.

Organic nitrogen uptake by arbuscular mycorrhizal fungi in a boreal forest

The breakdown of organic nitrogen in soil is a potential rate-limiting step in nitrogen cycling. Arbuscular mycorrhizal (AM) fungi are root symbionts that might improve the ability of plants to compete for organic nitrogen products against other decomposer microbes. However, AM uptake of organic nitrogen, especially in natural systems, has traditionally been difficult to test. We developed a novel quantitative nanotechnological technique to determine in situ that organic nitrogen uptake by AM fungi can occur to a greater extent than has previously been assumed. Specifically, we found that AM fungi acquired recalcitrant and labile forms of organic nitrogen. Moreover, N enrichment of soil reduced plot-scale uptake of these compounds. Since most plants host AM fungi, AM use of organic nitrogen could widely influence plant productivity, especially where N availability is relatively low.

接种AM真菌对玉米和油菜种间竞争及土壤无机磷组分的影响

在温室盆栽条件下,分别模拟单作、间作和尼龙网分隔种植,比较接种丛枝菌根(arbuscular mycorrhizal, AM)真菌<em>Glomus intraradices</em>和<em>Glomus mosseae</em>对菌根植物玉米和非菌根植物油菜生长和磷吸收状况的影响,并分析土壤中各无机磷组分的变化。结果发现,接种AM真菌可以促进土壤中难溶性磷(Ca₁₀-P和O-P)向有效态磷转化,并显著降低总无机磷含量 (<em>P</em><0.05),显著提高菌根植物玉米的生物量和磷吸收量(<em>P</em><0.05),特别是在间作体系中使玉米的磷营养竞争比率显著提高了45.0%-104.1% (<em>P</em><0.05),显著降低了油菜的生物量和磷吸收量(<em>P</em><0.05),从而增强了了菌根植物的竞争优势,降低了非菌根植物与菌根植物的共存能力。揭示了石灰性土壤中AM真菌对植物物种多样性的影响,有助于更加全面地理解AM真菌在农业生态系统中的作用。;Arbuscular mycorrhizal fungi (AMF) form mutualistic associations with more than 85% of terrestrial plant species and play key roles in nutrient cycling and ecosystem functioning. Most plant individual stimulates nutrient availability through their fungal partner. Highly mycorrhizal-dependent plant species derive more benefits from AMF in comparison to low mycorrhizal dependency plant species. But the effects of AMF on the competition between mycorrhizal and non-mycorrhizal plants remained largely unclear, particularly in an environment with low phosphate bioavailability. The increased phosphate availability for host plants and enhanced plant phosphorus nutrition is a major outcome of the AM symbiosis and then AMF colonization could and consequently increase plant biomass. The larger plants are then expected to be successful competitors. <br> In our previous, AMF colonization significantly decreased phosphorus concentration and content of rape roots compared with non-inoculation treatments, while in contrast mycorrhizal association improved phosphorus nutrition of maize plants. The results clearly showed the beneficial effects of mycorrhizal associations on AMF host plants in competition with non-host plants. In this previous research, plants were cultivated in purple soil with higher phosphorus availability which is more important as this determined the effect of AMF inoculation on host plant P nutrition. Then in this research, calcareous fluvo-aquic soil with lower phosphorus availability was used and different form of inorganic phosphorus were measured to reveal the effect of AMF inoculation on competition between mycorrhizal plant and non-mycorrhizal plants species. Maize (<em>Zea mays </em>L.) and rape (<em>Brassica napus </em>L.) plants were cultivated in three different interaction patterns, namely intraspecific (monoculture), intespecific (intercropping) and no interaction (nylon net split). All plants were inoculated with <em>Glomus intraradices</em>, <em>Glomus mosseae</em> or remained uninoculated. The strength of competition was measured as the reduction in biomass caused by the presence of a competitor. The results showed that AMF inoculation decreased soil inorganic phosphate significantly and transformed more Ca₁₀-P and O-P into higher availability phosphorus form. In the intercropping treatment, the inoculation improved the plant growth and phosphorus uptake of maize, and meanwhile decreased the growth and phosphorus uptake of rape significantly. Our results clearly showed the strong competitive strength and phosphorus competitive strength of maize to rape., and the beneficial effects of mycorrhizal associations was due to the favorable growth of host plants over non-host plants. It reveals that AM fungus may play an important role in structuring plant community and needs a comprehensive insight to understand the effect of AM fungus on plant biodiversity in ecosystems.