Dominant Arbuscular Mycorrhizal Research Articles

Effects of Different Arbuscular Mycorrhizal Fungi on Physiology of Viola prionantha under Salt Stress

Arbuscular mycorrhizal (AM) fungi distribute widely in natural habits and play a variety of ecological functions. In order to test the physiological response to salt stress mediated by different AM fungi, Viola prionantha was selected as the host, the dominant AM fungus in the rhizosphere of V. philippica growing in Songnen saline-alkali grassland, Rhizophagus irregularis, and their mixtures were used as inoculants, and NaCl stress was applied after the roots were colonized. The results showed that V. philippica could be colonized by AM fungi in the field and the colonization rate ranged from 73.33% to 96.67%, and Claroideoglomus etunicatum was identified as the dominant AM fungi species in the rhizosphere of V. philippica by morphology combined with sequencing for AM fungal AML1/AML2 target. Inoculation with both the species resulted in the formation of mycorrhizal symbiosis (the colonization rate was more than 70%) and AM fungi significantly enhanced plants’ tolerance to salt stress of varying magnitude. Higher activity of antioxidant enzymes and augmented levels of proline and other osmoregulators were observed in AM plants. The content of MDA in CK was higher than that in the inoculations with the stress of 100, 200, and 250 mM. All indices except soluble protein content and MDA content were significantly correlated with AM fungal colonization indices. The analysis for different AM fungal effects showed that the mixtures and R. irregularis worked even better than C. etunicatum. These results will provide theoretical support for the exploration and screening of salt-tolerant AM fungi species and also for the application of AM-ornamental plants in saline-alkali urban greening.

Arbuscular Mycorrhizal Fungal Colonization at Different Succession Stages in Songnen Saline-Alkali Grassland

Arbuscular mycorrhizal (AM) fungi can form symbiosis with 90% of the vascular plants and play important roles in ecosystem. To realize the AM fungal colonization at different succession stages in saline-alkali land and screen AM fungi species with great functions, roots and soil samples were collected from the three succession stages of Songnen saline-alkali grassland. The soil properties and AM fungal colonization were measured, and the fungus distributed extensively in three stages was annotated by sequencing for AML1/AML2 target, subsequently, maize was selected as the host to verify its colonization. The results showed that the soil properties improved with the succession of saline-alkali grassland. The plants’ communities of the three stages could be colonized by AM fungi, and the colonization rate of Leymus chinensis (the third stage) ranged from 66.67% to 100%, Puccinellia tenuiflora (the second stage) ranged from 50% to 80%, while the Suaeda glauca (the first stage) was only 35%–60%. Glomeraceae sp1 was identified as the dominant AM fungi species which occurred frequently in the succession of saline-alkali land with the isolation frequency, relative abundance, and importance value of 100%, 18.1%, and 59.1%, respectively. The colonization rate of Glomeraceae sp1 in maize ranged from 80% to 87% and similar mycorrhizal characteristics were detected in the roots of P. tenuiflora, S. glauca, and L. chinensis, indicating that Glomeraceae sp1 colonized the samples in the field. The correlation matrix indicated that colonization rate, colonization intensity, and vesicle abundance were closely related to soil conditions most, and they were related significantly to all the soil properties except cellulase activity. Besides, redundancy analysis (RDA) showed that soil properties drove the changes of AM fungal colonization and sporulation. These results will provide theoretical support for realizing the relationship between AM fungal colonization and soil conditions, and also for the exploration of AM fungi species with great functions.

Community Assembly of Fungi and Bacteria along Soil-Plant Continuum Differs in a Zoige Wetland.

ABSTRACTDistinct plant associated microbiomes live in rhizosphere soil, roots, and leaves. However, the differences in community assembly of fungi and bacteria along soil-plant continuum are less documented in ecosystems. We examined fungal and bacterial communities associated with leaves, roots, and rhizosphere soil of the dominant arbuscular mycorrhizal (AM) plants Taraxacum mongolicum and Elymus nutans and non-AM plant Carex enervis in the Zoige Wetland by using high throughput sequencing techniques. The operational taxonomic unit (OTU) richness of fungi and bacteria was significantly higher in rhizosphere soil than in roots and leaves, and their community compositions were significantly different in the rhizosphere soil, roots, and leaves in each plant species. The co-occurrence network analysis revealed that the sensitive fungal and bacterial OTUs with various taxonomic positions were mainly clustered into different modules according to rhizosphere soil, roots, and leaves in each plant species. Along the soil-plant continuum, the rhizosphere soil pool contributed more source on bacterial than on fungal communities in roots and leaves of the three plant species, and more source on bacterial and fungal communities in leaves of T. mongolicum and E. nutans compared with C. enervis. Furthermore, the root pool contributed more source on bacterial than on fungal communities in leaves of T. mongolicum and E. nutans but not that of C. enervis. This study highlights that the host plant selection intensity is higher in fungal than in bacterial communities in roots and leaves from rhizosphere soil in each plant species, and differs in fungal and bacterial communities along the soil-plant continuum in AM plants T. mongolicum and E. nutans and non-AM plant C. enervis in the Zoige Wetland.IMPORTANCE Elucidating the community microbiome assemblage alone the soil-plant continuum will help to better understand the biodiversity maintenance and ecosystem functioning. Here, we examined the fungal and bacterial communities in rhizosphere soil, roots, and leaves of two dominant AM plants and a non-AM plant in Zoige Wetland. We found that along the soil – plant continuum, host plant selection intensity is higher in fungal than in bacterial communities in roots and leaves from rhizosphere soil in each plant species, and differs in fungal and bacterial communities in the AM- and non-AM plants. This is the first report provides evidence of different assembly patterns of fungal and bacterial communities along the soil-plant continuum in the AM- and non-AM plants in the Zoige Wetland.

Dominance of arbuscular mycorrhizal fungi is key for Mongolian steppe management under livestock grazing, as indicated by ecosystem multifunctionality

Livestock grazing of drylands supports millions of livelihoods worldwide; however, overgrazing causes severe biodiversity loss and degrades ecosystem functions. Understanding the effects of grazing intensity, aridity, and soil microbes is required for sustainable management. Here, we focused on arbuscular mycorrhizal (AM) fungi in soils and roots and examined their relationship with ecosystem multifunctionality under livestock grazing of Mongolian grasslands with different aridity levels. Above- and below-ground plant biomass were used to measure ecosystem-service multifunctionality, excluding annual plants that are unfavorable for ecosystem function and rangeland management. In both mountain forest steppe (mean annual precipitation = 207.7 mm) and steppe–desert steppe transition zone (mean annual precipitation = 128.4 mm), ecosystem multifunctionality was decreased by livestock grazing, as indicated by palatable plant shoot biomass. In line with the multifunctionality, the dominant plant species, Stipa krylovii, and AM plant biomass were decreased by livestock grazing. The Berger–Parker dominance index of soil AM fungi and Simpson’s diversity had a positive and negative relationship with multifunctionality, respectively, indicating that dominant AM fungi rather than AM fungal diversity in soil are key for maintaining multifunctionality. Root and soil AM fungal communities were significantly different with dominance of Rhizophagus operational taxonomic units (OTUs) in roots and Claroideoglomus OTUs in soil. However, the similarity between soil and root AM fungal communities increased with livestock grazing. Correlation analysis between palatable plant biomass and relative abundance of dominant AM fungal OTUs identified indicator virtual taxa that decreased (VTX00325 in roots, and VTX00165, VTX00214, and VTX00222 in soil) or increased (VTX00100, VTX00130, and VTX00295 in soil) with grazing intensity. The OTUs that were increased by grazing may be r-selected, grazing-tolerant AM fungi that accept a low C supply and supply few nutrients to plants. Our results suggest that grassland management focusing on ecosystem-service multifunctionality via control of AM plants, including S. krylovii and their co-dominant dominant AM fungi, in ungrazed grasslands are key for sustainable rangeland management in Mongolia.

Soil properties and plant community-level traits mediate arbuscular mycorrhizal fungal response to nitrogen enrichment and altered precipitation

Despite the linkage of arbuscular mycorrhizal (AM) fungi to soil-plant interface, how changes in plant community-level traits and soil properties affect AM fungal communities under global changes remains largely unknown. Here, to investigate whether nitrogen (N) enrichment and altered precipitation can influence AM fungal communities through effects on plant community-level traits and soil properties, a six year-long factorial N and precipitation field experiment (N-addition rate: 10 g m−2 year−1; reduced precipitation by 50% and enhanced precipitation by 50%) was conducted in an alpine steppe of the Tibet Plateau. We observed that reduced precipitation decreased AM fungal diversities, while N enrichment decreased AM fungal biomass. Secondly, N enrichment and reduced precipitation shifted plant community composition from bunchgrass dominance (primarily Stipa purpurea) to rhizomatous grass dominance (primarily Leymus secalinus). N enrichment and reduced precipitation also led to a marked shift in AM fungal community composition. More specifically, reduced precipitation enhanced the relative abundance of the dominant taxa Glomus, while the relative abundance of Scutellospora and Diversispora was decreased. In contrast, N enrichment decreased the relative abundance of Scutellospora and Diversispora, while the relative abundance of Glomus was decreased. Structural equation models (SEMs) demonstrated that precipitation regime affected dominant AM fungal taxa via soil pH, while N enrichment affected dominant AM fungal taxa by changes in plant community-level traits. In addition, N- and precipitation-induced shifts in AM fungal community structure were significantly related to canopy photosynthetic rates and soil pH, indicating that canopy photosynthesis and soil pH may mediate the responses in AM fungal communities to enhanced N deposition and precipitation regime. Therefore, our findings may provide previously unidentified insights into N- and precipitation- evoked differential responses of AM fungal communities by linking plant community-level traits and soil properties.

Diversity of arbuscular mycorrhizal (AM) fungi in mangroves of Chorao Island, Goa, India

For a desirable understanding of diversity and species composition of arbuscular mycorrhizal (AM) fungi, in true and associate mangrove plants, 17 true mangrove and their associate species belonging to ten families were assessed from Chorao Island, Goa, India. Maximum AM root colonization was recorded in Thespesia populnea and minimum in Avicennia marina. Rhizosphere soils of Ceriops tagal showed highest and that of Acrostichum aureum showed the least spore density. The results showed that the associate mangrove species were highly mycorrhizal compared to true mangrove plants. Our study recorded greater diversity involving thirty-two AM fungal species belonging to nine genera viz., Acaulospora, Claroideoglomus, Entrophospora, Funneliformis, Gigaspora, Glomus, Rhizophagus, Sclerocystis, and Scutellospora. Acaulospora was the dominant genus and A. dilatata was the dominant AM fungal species. Acaulospora dilatata was the most common AM species in both true and associate mangrove plants, revealing its wider adaptability.

Arbuscular mycorrhizal fungal communities under gradients of grazing in Mongolian grasslands of different aridity.

Communities of arbuscular mycorrhizal (AM) fungi in Mongolian grassland were characterized under gradients of grazing intensity at three study sites of different aridity: mountain forest steppe at Hustai National Park (Hustai), and desert steppe at Mandalgovi and Bulgan. Grazing intensity was classified into three categories: lightly grazed (LG), moderately grazed (MG), and heavily grazed (HG). With regard to floristic composition, grazing decreased the shoot biomass of Poaceae species, especially Stipa spp. Distinctness of the AM fungal communities was observed among the three study sites, but most of the AM fungal operational taxonomic units (OTUs) that comprised over 1.0% of the total reads were ubiquitous. This result indicates that the AM fungal communities may be derived from similar AM fungal floras in correspondence with environmental factors. The composition of AM fungal communities differed significantly among the grazing intensities at all study sites. The relative abundance of the most dominant AM fungal OTU of the LG plots decreased with an increase in grazing intensity at all study sites. The mean proportions of the most dominant AM fungal OTUs also decreased with increased grazing intensity at Hustai. Dominance by a single AM fungal taxon may be a typical ecological feature of the AM fungal symbiosis, and grazing disturbs AM fungal community structure.

Funneliformis mosseae affects the root rot pathogen Fusarium oxysporum in soybeans

We analyzed the relationship between the dominant arbuscular mycorrhizal (AM) fungus Funneliformis mosseae and the dominant soybean root rot pathogen Fusarium oxysporum through the pot trials to help overcome obstacles to continuous cropping of soybean and to provide theoretical evidence that can be used to help prevent the reduced production induced by soybean root rot. Using qRT-PCR, we amplified the specific rDNA sequences of F. mosseae and F. oxysporum in soybean roots and rhizosphere soil and quantified the DNA contents of these fungi to determine the relationship between the dominant AM fungus F. mosseae and F. oxysporum. The DNA contents of F. oxysporum differed significantly depending on the presence of F. mosseae in both soybean roots and rhizosphere soil. Specifically, the DNA contents of F. oxysporum were reduced after inoculation with F. mosseae, suggesting that F. mosseae has a negative effect on the growth of F. oxysporum.

Diversity of rhizosphere soil arbuscular mycorrhizal fungi in various soybean cultivars under different continuous cropping regimes.

Recent studies have shown that continuous cropping in soybean causes substantial changes to the microbial community in rhizosphere soil. In this study, we investigated the effects of continuous cropping for various time periods on the diversity of rhizosphere soil arbuscular mycorrhizal (AM) fungi in various soybean cultivars at the branching stage. The soybean cultivars Heinong 37 (an intermediate cultivar), Heinong 44 (a high-fat cultivar) and Heinong 48 (a high-protein cultivar) were seeded in a field and continuously cropped for two or three years. We analyzed the diversity of rhizosphere soil AM fungi of these soybean plants at the branching stage using morphological and denaturing gradient gel electrophoresis (DGGE) techniques. The clustering analysis of unweighted pair-group method with arithmetic averages (UPGMA) was then used to investigate the AM fungal community shifts. The results showed that increasing the number of years of continuous cropping can improve the colonization rate of AM fungi in different soybean cultivars at the branching stage. The dominant AM fungi in the experimental fields were Funneliformismosseae and Glomus spp. The number of years of continuous cropping and the soybean cultivar both had obvious effects on the diversity of AM fungi, which was consistent with the results of colonization rate analysis. This study establishes a basis for screening dominant AM fungi of soybean. In addition, the results of this study may be useful for the development of AM fungal inoculants.

Microbial community structure in the rhizosphere of Sophora viciifolia grown at a lead and zinc mine of northwest China

Understanding the effects of heavy metal contamination on microbial activity is important for developing strategies to reclaim sites disturbed by industrial activities. In this study, we investigated arbuscular mycorrhizal (AM) fungi and bacteria associated with Sophora viciifolia growing at a lead and zinc mine in Qinling Mountain, China. Specifically, we measured the extent of AM fungal root colonization, examined microbial community structure by PCR-denaturing gradient gel electrophoresis (PCR-DGGE), and identified the dominant microorganisms. We also measured the amount of glomalin-related soil protein (GRSP) and the association of GRSP with heavy metal ions. We found that AM root colonization decreased, but total GRSP increased with the increase of the lead concentration in soil. The Shannon–Wiener Index (H′) of the AM fungal community showed a significant negative correlation with the available lead concentration (r=0.92, P=0.009). Bacterial community H′ was also negatively correlated with the total and available lead concentrations in the soil (r=0.97, P=0.007 and r=0.92, P=0.025 for total and available lead, respectively). Both, AM fungal and bacterial community structures differed significantly between sites along the pollution gradient. The specific distributions of the two kinds of organisms indicated their differing tolerances to heavy metal. The dominant AM fungi were identified as Glomeraceae, whereas the dominant bacteria belonged to Proteobacteria. The amount of lead bound to GRSP varied from 3.3 to 172.5mgkg−1, which positively correlated with total and available soil lead concentration (r=0.99, P<0.000 and r=0.93, P=0.020 for total soil lead and available soil lead concentration, respectively), thus reducing the bioavailability of heavy metal ions.

Arbuscular mycorrhizal fungi assemblages in Chernozem great groups revealed by massively parallel pyrosequencing

The arbuscular mycorrhizal (AM) fungal resources present in wheat fields of the Canadian Prairie were explored using 454 pyrosequencing. Of the 33 dominant AM fungal operational taxonomic units (OTUs) found in the 76 wheat fields surveyed at anthesis in 2009, 14 clustered as Funneliformis - Rhizophagus, 16 as Claroideoglomus, and 3 as Diversisporales. An OTU of Funneliformis mosseae and one OTU of Diversisporales each accounted for approximately 16% of all AM fungal OTUs. The former was ubiquitous, and the latter was mainly restricted to the Black and Dark Brown Chernozems. AM fungal OTU community composition was better explained by the Chernozem great groups (P = 0.044) than by measured soil properties. Fifty-two percent of the AM fungal OTUs were unrelated to measured soil properties. Black Chernozems hosted the largest AM fungal OTU diversity and almost twice the number of AM fungal sequences seen in Dark Brown Chernozems, the great group ranking second for AM fungal sequence abundance. Brown Chernozems hosted the lowest AM fungal abundance and an AM fungal diversity as low as that seen in Gray soils. We concluded that Black Chernozems are most conducive to AM fungal proliferation. AM fungi are generally distributed according to Chernozem great groups in the Canadian Prairie, although some taxa are evenly distributed in all soil groups.

Arbuscular mycorrhizal fungal diversity in some commonly occurring medicinal plants of Western Ghats, Goa region

Thirty-six medicinal plant species belonging to 25 families were surveyed to study Arbuscular mycorrhizal (AM) fungal diversity from different localities of North and South Goa of Western Ghats, Goa region, India. A total of 30 medicinal plant species were found to be mycorrhizal and six plant species showed absence of AM fungal colonization. Forty two AM fungal species belonging to five genera viz., Glomus, Acaulospora, Scutellospora, Gigaspora and Ambispora were recovered from the rhizosphere soil. Glomus was found to be the most dominant genera in the study sites, and Glomus fasciculatum the most dominant AM fungal species. Negative significant correlation was observed between percent colonization and spore density. Simpson’s and Shannon Weiner diversity index studies carried out in North and South Goa exhibited less variation in both the sites, indicating a stable and a diverse plant community.

Idiosyncrasy and overdominance in the structure of natural communities of arbuscular mycorrhizal fungi: is there a role for stochastic processes?

Summary 1. Most studies of species abundance patterns focus on conspicuous macroorganisms while microbial communities remain relatively understudied. This bias is a concern given the functional importance and high diversity of microbes. 2. We determine whether a common species abundance distribution (SAD) is observed in communities of a widespread group of soil microbes, the Glomeromycota or arbuscular mycorrhizal (AM) fungi. Using molecular techniques, we intensively sampled the AM fungal community of a woodland–grassland ecotone in Yorkshire, UK. Observed species abundances were compared to theoretical models describing SADs. We also reanalysed 32 previously published data sets in a similar manner. 3. Species abundance distributions in all the AM fungal communities fitted both lognormal and broken‐stick models. However, these models consistently and significantly underpredicted the abundance of the most abundant AM fungal taxon. We found that AM fungal communities are typically dominated by a single taxon; representing on average 40% of total abundance within the community. Phylogenetic analysis of the most abundant taxa across data sets showed that the dominant AM fungal type in each community was different and not a widespread generalist. 4. We conclude that a common community structure is present in AM fungal communities from different habitats. The fit to log‐normal and broken‐stick models suggests the influence of niche differentiation structuring these communities. However, the consistently observed overdominance indicates that local adaptation and stochastic processes may also play important roles in structuring these communities, and we propose a mechanism to explain overdominance in AM fungal communities. 5. Synthesis. This paper applies ecological models derived from studies on larger organisms to microbial communities. Results from this study suggest that a common log‐normal SAD is likely to be observed across both microbial and macro taxa. However, due to the distinctive features of microbial biology, some noticeable differences, such as heavy overdominance, may lead to unique structures in microbial communities. This research not only highlights that, to a first approximation, microbial communities follow similar processes and have similar patterns to those of macroorganisms, but also the need for large‐scale microbial data sets, if we are to understand the patterns and processes regulating global biodiversity.

Diversity of endomycorrhizal fungi and their synergistic effect on the growth of Acacia catechu Willd.

The diversity of arbuscular mycorrhizal (AM) fungi of &lt;I&gt;Acacia catechu&lt;/I&gt; Willd. was studied. Dominant AM spores, the bacterium &lt;I&gt;Rhizobium&lt;/I&gt; sp. along with the fungus &lt;I&gt;Trichoderma viride&lt;/I&gt; were isolated from the rhizosphere of &lt;I&gt;A. catechu&lt;/I&gt; and mass-produced in laboratory. The co-inoculation effect of &lt;I&gt;Glomus mosseae, Glomus fasciculatum&lt;/I&gt;, mixed AM (&lt;I&gt;Glomus&lt;/I&gt; spp. [except &lt;I&gt;G. mosseae, G. fasciculatum&lt;/I&gt;] with &lt;I&gt;Acaulospora&lt;/I&gt; spp., &lt;I&gt;Sclerocystis&lt;/I&gt; spp. and &lt;I&gt;Gigaspora&lt;/I&gt; spp.), &lt;I&gt;Rhizobium&lt;/I&gt; sp. and &lt;I&gt;Trichoderma viride&lt;/I&gt; was studied as exerted on the growth of &lt;I&gt;A. catechu&lt;/I&gt; seedlings. All inoculated seedlings showed improved seedling growth compared to the control. Inoculated seedlings had a pronounced effect on all growth parameters such as height, fresh and dry weight of roots and shoots, AM spore count, per cent mycorrhizal colonization in roots and root nodule number in comparison with uninoculated seedlings. Phosphorus uptake was also higher in inoculated seedlings than in the control. This study provides a good scope for commercially utilizing the efficient strains of AM fungi for beneficial effects with other beneficial rhizosphere microflora in the primary establishment of slow growing seedlings ensuring better survival and improved growth.

Arbuscular mycorrhizal fungi associated with wild forage plants in typical steppe of eastern Inner Mongolia

A preliminary investigation was conducted on the arbuscular mycorrhizal (AM) status of the dominant and common wild forage plants in typical steppe of eastern Inner Mongolia, a major semi-arid grassland region in China. Fifty-four wild forage plant species were collected and examined, and 27 of these were colonized by AM fungi. Some plants belonging to families that are presumed to lack mycorrhizas (Cyperaceae, Caryophyllaceae and Chenopodiaceae) were also found to be mycorrhizal. Higher proportions of arbuscular mycorrhizal plants were found in perennial (56.1%) and monocotyledonous (64.7%) forage species. However, neither percentage of root length colonized nor spore density varied significantly between the two life forms or cotyledon types. Twenty-seven species belonging to 7 genera of AM fungi were identified in total according to the morphological characteristics of the spores from field soil and trap cultures, and the results indicate that Glomus was the dominant AM genus and Glomus geosporum (Nicolson & Gerdemann) Walker and Glomus mosseae (Nicolson & Gerdemann) Gerdemann & Trappe were the dominant species in field soil and trap cultures, respectively. Glomus intraradices Schenck & Smith, Glomus etunicatum Becher & Gerdemann, Glomus claroideum Schenk & Smith emend Walker & Vestberg, Glomus clarum Nicolson & Schenck and Scutellospora callospora (Nicolson & Gerdemann) Walker & Sanders also occurred with high frequencies.

5E-5 Influence of feeding practices on insulin resistance in low birthweight neonates

A field study of traditional agroforestry systems in six districts of the arid and semiarid zones of Rajasthan was undertaken where annual rainfall varied from 140 to 1000 mm and soil types ranged from coarse fine sand in Jaisalmer to clay loams in Kota. The field investigation showed that Glomus, Gigaspora and Sclerocystis were the genera of arbuscular mycorrhizal fungi present in the neem-based agroforestry system. Among the three genera, Glomus occurred most frequently, with 15 species of Glomus, 3 of Gigaspora and 2 of Sclerocystis observed. Glomus fasciculatum was the predominant arbuscular mycorrhizal (AM) fungus infecting neem. Of the six districts surveyed, five had the highest diversity index of G. fasciculatum, at sites where Sclerocystis species were present in districts of low rainfall, viz. Jaisalmer, Barmer and Jodhpur. The maximum spore density in the neem tree rhizosphere was in Jodhpur and the minimum in Kota. However, in the crop rhizosphere the maximum was in Jaipur and the minimum in Jaisalmer. At all sites, spore density was greater in tree and crop rhizospheres than in the soils of uncropped sites. Infection was higher in tree roots than crop roots. The factors Fe, Zn and maximum temperatures affected the AM fungal populations significantly in the neem rhizosphere. In associated crop rhizospheres electrical conductivity (EC), organic C, Fe, P, CaCO3, maximum temperature, rainfall and humidity affected the AM populations. The results indicate that G. fasciculatum was the dominant stable AM fungus in these areas.

Diversity of arbuscular mycorrhizal fungi associated with desert ephemerals in plant communities of Junggar Basin, northwest China

Colonization by and diversity of arbuscular mycorrhizal (AM) fungi associated with five common ephemerals, Eremopyrum orientale (L.) Jaub. et Spach., Gagea sacculifera Regel., Plantago minuta Pall., Tragopogon kasahstanicus S. Nikit., and Trigonella arcuata C. A. Mey. were investigated in four typical desert plant communities in Junggar Basin, northwest China. All five ephemerals examined were found to be colonized and formed typical arbuscules or vesicles. The proportion of root length colonized ranged from 2 to 85% with an average of 19%. Spore density in soil near the roots of different ephemerals varied from 1 to 120 spores per 20 ml soil, with an average value of 33 spores. Species richness averaged 8.8 AM fungal species in soil near the roots and ranged from 2 to 21. Fifty-four AM fungal taxa belonging to the genera Acaulospora, Archaeospora, Entrophospora, Glomus and Paraglomus were isolated and identified from soil around the roots. Glomus was the dominant AM fungal genus with a frequency of 100% and relative abundance of 82.6%. The AM fungal species with the highest frequency of occurrence was Glomus aggregatum with a frequency of 75%. G. microaggregatum was present in the highest relative abundance (16%). G. sacculifera, P. minuta and T. arcuata formed Arum-type mycorrhizas. Arbuscular mycorrhizal fungi are ubiquitous and Arum-type mycorrhizas are especially prevalent in these important desert communities used for grazing and traditional medicine.

Links between tree species, symbiotic fungal diversity and ecosystem functioning in simplified tropical ecosystems

We studied the relationships among plant and arbuscular mycorrhizal (AM) fungal diversity, and their effects on ecosystem function, in a series of replicate tropical forestry plots in the La Selva Biological Station, Costa Rica. Forestry plots were 12 yr old and were either monocultures of three tree species, or polycultures of the tree species with two additional understory species. Relationships among the AM fungal spore community, host species, plant community diversity and ecosystem phosphorus-use efficiency (PUE) and net primary productivity (NPP) were assessed. Analysis of the relative abundance of AM fungal spores found that host tree species had a significant effect on the AM fungal community, as did host plant community diversity (monocultures vs polycultures). The Shannon diversity index of the AM fungal spore community differed significantly among the three host tree species, but was not significantly different between monoculture and polyculture plots. Over all the plots, significant positive relationships were found between AM fungal diversity and ecosystem NPP, and between AM fungal community evenness and PUE. Relative abundance of two of the dominant AM fungal species also showed significant correlations with NPP and PUE. We conclude that the AM fungal community composition in tropical forests is sensitive to host species, and provide evidence supporting the hypothesis that the diversity of AM fungi in tropical forests and ecosystem NPP covaries.

Arbuscular mycorrhizal fungal diversity in neem-based agroforestry systems in Rajasthan

A field study of traditional agroforestry systems in six districts of the arid and semiarid zones of Rajasthan was undertaken where annual rainfall varied from 140 to 1000 mm and soil types ranged from coarse fine sand in Jaisalmer to clay loams in Kota. The field investigation showed that Glomus, Gigaspora and Sclerocystis were the genera of arbuscular mycorrhizal fungi present in the neem-based agroforestry system. Among the three genera, Glomus occurred most frequently, with 15 species of Glomus, 3 of Gigaspora and 2 of Sclerocystis observed. Glomus fasciculatum was the predominant arbuscular mycorrhizal (AM) fungus infecting neem. Of the six districts surveyed, five had the highest diversity index of G. fasciculatum, at sites where Sclerocystis species were present in districts of low rainfall, viz. Jaisalmer, Barmer and Jodhpur. The maximum spore density in the neem tree rhizosphere was in Jodhpur and the minimum in Kota. However, in the crop rhizosphere the maximum was in Jaipur and the minimum in Jaisalmer. At all sites, spore density was greater in tree and crop rhizospheres than in the soils of uncropped sites. Infection was higher in tree roots than crop roots. The factors Fe, Zn and maximum temperatures affected the AM fungal populations significantly in the neem rhizosphere. In associated crop rhizospheres electrical conductivity (EC), organic C, Fe, P, CaCO 3, maximum temperature, rainfall and humidity affected the AM populations. The results indicate that G. fasciculatum was the dominant stable AM fungus in these areas.