AMF Communities Research Articles

Commercial bioinoculants improve colonization but do not alter the arbuscular mycorrhizal fungal community of greenhouse-grown grapevine roots

BackgroundArbuscular mycorrhizal fungi (AMF) are beneficial root symbionts contributing to improved plant growth and development and resistance to abiotic and biotic stresses. Commercial bioinoculants containing AMF are widely considered as an alternative to agrochemicals in vineyards. However, their effects on grapevine plants grown in soil containing native communities of AMF are still poorly understood. In a greenhouse experiment, we evaluated the influence of five different bioinoculants on the composition of native AMF communities of young Cabernet Sauvignon vines grown in a non-sterile soil. Root colonization, leaf nitrogen concentration, plant biomass and root morphology were assessed, and AMF communities of inoculated and non-inoculated grapevine roots were profiled using high-throughput sequencing.ResultsContrary to our predictions, no differences in the microbiome of plants exposed to native AMF communities versus commercial AMF bioinoculants + native AMF communities were detected in roots. However, inoculation induced positive changes in root traits as well as increased AMF colonization, plant biomass, and leaf nitrogen. Most of these desirable functional traits were positively correlated with the relative abundance of operational taxonomic units identified as Glomus, Rhizophagus and Claroideoglomus genera.ConclusionThese results suggest synergistic interactions between commercial AMF bioinoculants and native AMF communities of roots to promote grapevine growth. Long-term studies with further genomics, metabolomics and physiological research are needed to provide a deeper understanding of the symbiotic interaction among grapevine roots, bioinoculants and natural AMF communities and their role to promote plant adaptation to current environmental concerns.

Microbial community structure in recovering forests of Mount St. Helens

IntroductionThe 1980 eruption of Mount St. Helens had devastating effects above and belowground in forested montane ecosystems, including the burial and destruction of soil microbes. Soil microbial propagules and legacies in recovering ecosystems are important for determining post-disturbance successional trajectories. Soil microorganisms regulate nutrient cycling, interact with many other organisms, and therefore may support successional pathways and complementary ecosystem functions, even in harsh conditions. Historic forest management methods, such as old-growth and clearcut regimes, and locations of small mammal enclo and clearcut forests, as well as in locations of historic short-term gopher enclosures (Thomomys talpoides), to evaluate community response to forest management practices and to examine vectors for dispersing microbial consortia to the surface of the volcanic landscape. These biotic interactions may have primed ecological succession in the volcanic landscape, specifically Bear Meadow and the Pumice Plain, by creating microsite conditions conducive to primary succession and plant establishment.Methods and resultsUsing molecular techniques, we examined bacterial, fungal, and AMF communities to determine how these variables affected microbial communities and soil properties. We found that bacterial/archaeal 16S, fungal ITS2, and AMF SSU community composition varied among forestry practices and across sites with long-term lupine plots and gopher enclosures. The findings also related to detected differences in C and N concentrations and ratios in soil from our study sites. Fungal communities from previously clearcut locations were less diverse than in gopher plots within the Pumice Plain. Yet, clearcut meadows harbored fewer ancestral AM fungal taxa than were found within the old-growth forest.DiscussionBy investigating both forestry practices and mammals in microbial dispersal, we evaluated how these interactions may have promoted revegetation and ecological succession within the Pumice Plains of Mount St. Helens. In addition to providing evidence about how dispersal vectors and forest structure influence post-eruption soil microbiomes, this project also informs research and management communities about belowground processes and microbial functional traits in facilitating succession and ecosystem function.

Arbuscular Mycorrhizal Fungi Diversity in Sophora japonica Rhizosphere at Different Altitudes and Lithologies.

Arbuscular mycorrhizal fungi play a key role in mediating soil-plant relationships within karst ecosystems. Sophora japonica, a medicinal plant with anti-inflammatory and antitumor properties, is widely cultivated in karst areas of Guangxi, China. We considered limestone, dolomite, and sandstone at altitudes ranging from 100 to 800 m and employed Illumina sequencing to evaluate AMF diversity and identify the factors driving S. japonica rhizosphere AMF community changes. We showed that the increase in altitude increased S. japonica AMF colonization and the Shannon index. The colonization of limestone plots was higher than that of other lithology. In total, 3,096,236 sequences and 5767 OTUs were identified in S. japonica rhizosphere soil. Among these, 270 OTUs were defined at the genus level and divided into 7 genera and 35 species. Moreover, available nitrogen, soil organic matter, and available calcium content had a coupling effect and positive influence on AMF colonization and Shannon and Chao1 indices. Conversely, available phosphorus, available potassium, and available magnesium negatively affected AMF Shannon and Chao1 indices. Lithology, altitude, pH, and available phosphorus are important factors that affect the dynamics of AMF in the S. japonica rhizosphere.

Microorganism community structure: A characterisation of agrosystems from Madeira Archipelago.

Microbial diversity profoundly influences soil ecosystem functions, making it vital to monitor community dynamics to comprehend its structure. Our study focused on six agrosystems in Madeira Archipelago, analysing bacteria, archaea, fungi and AMF through classical microbiology and molecular techniques. Despite distinct edaphoclimatic conditions and management practices, bacterial structures exhibited similarities, with Alphaproteobacteria at 18%-20%, Bacilli at 11%-18% and Clostridia at 9%-14%. The predominance of copiothrophic groups suggested that soil nutrient content was the driver of these communities. Regarding archaea, the communities changed among sites, and it was evident that agrosystems provided niches for methanogens. The Crenarchaeota varied between 15% and 29%, followed by two classes of Euryarchaeota, Methanomicrobia (17%-25%) and Methanococci (4%-32%). Fungal communities showed consistent composition at the class level but had differing diversity indices due to management practices and soil texture. Sordaryomycetes (21%-28%) and Agaricomycetes (15%-23%) were predominant. Conversely, AMF communities appeared to be also influenced by the agrosystem, with Glomus representing over 50% of the community in all agrosystems. These insights into microbial groups' susceptibilities to environmental conditions are crucial for maintaining healthy soil and predicting climate change effects on agrosystems' productivity, resilience and sustainability. Additionally, our findings enable the development of more robust prediction models for agricultural practices.

Arbuscular mycorrhizal fungi communities vary between poplar species in the same habitat

The species diversity of AMF is influenced by the cultivar of the host plant. For this study, six species of poplar (Populus spp.) were selected from the poplar germplasm conservation experimental forest in Tongzhou, Beijing, China. The aim of the study was to compare the chemical characteristics of the poplar stand soils, including total carbon, total nitrogen, total phosphorus, and available phosphorus. The composition of the AMF community was also analyzed using high-throughput sequencing techniques. Significant differences in soil nutrient content (total phosphorus, available phosphorus, carbon/nitrogen, carbon/phosphorus) were found between different species of Populus spp. (p < 0.05), although the total carbon, total nitrogen, and nitrogen/phosphorus of the soil did not differ significantly (p > 0.05). Notably, the Simpson index and Pielou index of the AMF community exhibited the most significant differences among the various poplar cultivars, with the highest mean values for P. × euramericana cl. ‘J6’ (0.98 and 0.77, respectively). Furthermore, significant correlations were observed between the relative abundance of AMF communities at each taxonomic level and soil nutrient content. At the generic level, the relative abundance of Glomus has the highest correlation with C/N and C/P (r = −0.79). Overall, the findings of this study highlight the impact of poplar species on the composition and structure of the soil AMF community, which is closely related to soil nutrient content. These results contribute to our understanding of the plant–AMF–soil interaction mechanisms and provide a solid basis for future research in this field.

Effect the accumulation of bioactive constituents of a medicinal plant (Salvia Miltiorrhiza Bge.) by arbuscular mycorrhizal fungi community

BackgroundArbuscular mycorrhizal fungi (AMF) form symbiotic relationships with various terrestrial plants and have attracted considerable interest as biofertilizers for improving the quality and yield of medicinal plants. Despite the widespread distribution of AMFs in Salvia miltiorrhiza Bunge's roots, research on the impact of multiple AMFs on biomass and active ingredient accumulations has not been conducted. In this study, the effects of five native AMFs (Glomus formosanum, Septoglomus constrictum, Rhizophagus manihotis, Acaulospora laevis, and Ambispora gerdemannii) and twenty-six communities on the root biomass and active ingredient concentrations of S. miltiorrhiza were assessed using the total factor design method.ResultsThirty-one treatment groups formed symbiotic relationships with S. miltiorrhiza based on the pot culture results, and the colonization rate ranged from 54.83% to 89.97%. AMF communities had higher colonization rates and total phenolic acid concentration than single AMF, and communities also appeared to have higher root fresh weight, dry weight, and total phenolic acid concentration than single inoculations. As AMF richness increased, there was a rising trend in root biomass and total tanshinone accumulations (ATTS), while total phenolic acid accumulations (ATP) showed a decreasing trend. This suggests that plant productivity was influenced by the AMF richness, with higher inoculation benefits observed when the communities contained three or four AMFs. Additionally, the affinities of AMF members were also connected to plant productivity. The inoculation effect of closely related AMFs within the same family, such as G. formosanum, S. constrictum, and R. manihotis, consistently yielded lower than that of mono-inoculation when any combinations were applied. The co-inoculation of S. miltiorrhiza with nearby or distant AMFs from two families, such as G. formosanum, R. manihotis, and Ac. laevis or Am. gerdemannii resulted in an increase of ATP and ATTS by more than 50%. AMF communities appear to be more beneficial to the yield of bioactive constituents than the single AMF, but overall community inoculation effects are related to the composition of AMFs and the relationship between members.ConclusionThis study reveals that the AMF community has great potential to improve the productivity and the accumulation of bioactive constituents in S. miltiorrhiza, indicating that it is an effective way to achieve sustainable agricultural development through using the AMF community.

Co-occurring tree species drive arbuscular mycorrhizal fungi diversity in tropical forest.

It is still uncertain whether environment or host plant species is more important in determining AMF diversity; although, plant roots are usually associated with abundant AMF species in different environments. This study explored the effect of plant species and environmental factors on AMF diversity based on three co-occurring tree species (Glochidion coccineum, Schefflera octophylla, and Schima superba) on six elevations of Mt. Jianfengling. A total of 185 OTUs (operational taxonomic units) of AMF were found in the three co-occurring dominant tree species. Of which 109 unique OTUs were identified in the three co-occurring plant species, which accounted for the total number of 58.92%. Forty-five OTUs were shared by the three co-occurring tree species, accounting for a total number of 24.32%. The plant species of Schefflera octophylla was identified as having the highest AMF diversity with the largest number of OTUs of 143. The fungi in the genus of Glomus were the dominant AMF species in the three co-occurring tree species. AMF communities and diversity are quite different, either within different plant species at the same elevation or within the same plant species at different elevations. However, the altitude had no significant effect on the ACE index. Therefore, the results suggest that plant species have a more important effect on AMF diversity and community composition.

Responses of rhizosphere fungi to the root economics space in grassland monocultures of different age.

Recent studies on root traits have shown that there are two axes explaining trait variation belowground: the collaboration axis with mycorrhizal partners and the conservation ('fast - slow') axis. However, it is yet unknown whether these trait axes affect the assembly of soilborne fungi. We expect saprotrophic fungi to link to the conservation axis of root traits, whereas pathogenic and arbuscular mycorrhizal fungi link to the collaboration axis, but in opposite directions, as arbuscular mycorrhizal fungi might provide pathogen protection. To test these hypotheses, we sequenced rhizosphere fungal communities and measured root traits in monocultures of 25 grassland plant species, differing in age. Within the fungal guilds, we evaluated fungal species richness, relative abundance and community composition. Contrary to our hypotheses, fungal diversity and relative abundance were not strongly related to the root trait axes. However, saprotrophic fungal community composition was affected by the conservation gradient and pathogenic community composition by the collaboration gradient. The rhizosphere AMF community composition did not change along the collaboration gradient, even though the root trait axis was in line with the root mycorrhizal colonization rate. Overall, our results indicate that in the long term, the root trait axes are linked with fungal community composition.

The structure and ecological function of the interactions between plants and arbuscular mycorrhizal fungi through multilayer networks

Abstract Arbuscular mycorrhizas are one of the most frequent mutualisms in terrestrial ecosystems. Although studies on plant mutualistic interaction networks suggest that they may leave their imprint on plant community structure and dynamics, this has not been explicitly assessed. Thus, in the context of plant‐fungi interactions, studies explicitly linking plant‐mycorrhizal fungi interaction networks with key ecological functions of plant communities, such as recruitment, are lacking. In this study, we analyse, in two Mediterranean forest communities of southern Iberian Peninsula, how plant‐arbuscular mycorrhizal fungi (AMF) networks modulate plant‐plant recruitment interaction networks. We use a new approach integrating plant‐AMF and plant recruitment networks into a single multilayer structure. We also develop a new metric (Interlayer Node Neighbourhood Integration, INNI) to explore the impact of a given node on the structure across layers. The similarity of plant species in their AMF communities is positively related to the observed frequency of recruitment interactions in the field. Results reveal that properties of plant‐AMF networks, such as plant degree and centrality, can explain about the properties of plant recruitment network, such as in‐ and out‐degree (i.e. sapling bank and canopy service) and its modular structure. However, these relationships differed between the two forest communities. Finally, we identify particular AMF that contribute to integrate the neighbourhood of recruitment interactions between plants. This multilayer network approach is useful to explore the role of plant‐AMF interactions on recruitment, a key ecosystem function enhanced by fungi. Results provide evidence that the complex structure of plant‐AMF interactions impacts functional and structurally plant‐plant interactions, which in turn may potentially influence plant community dynamics, through their effects on the structure of the recruitment network. Read the free Plain Language Summary for this article on the Journal blog.

Characteristics of the soil arbuscular mycorrhizal fungal community along succession stages in tropical forest and its driving factors

Arbuscular mycorrhizal fungi play an important role in mediating plant-soil interactions across succession stages. However, AMF community dynamics which about the change of community composition and member activity remain unclear. To complete the gap knowledge about microbial community dynamics during restoration succession, soil AMF community composition was studied within a tropical forest ecosystem in the Ganshiling nature reserve using high throughput sequencing methods. The results revealed that soil AMF communities characteristics about speices diversity, species composition and microbial correlation network showed significant differences between shrubland (SC) and secondary forest ecosystems, but the same differences were not found between 40-year recovery secondary forest (SF40) and 60-year recovery secondary forest (SF60). Plant community dynamics were the key factor for regulating soil AMF communities among succession stages. An important biotic factor explaining variance in AMF community composition was root biomass. The correlation network analysis showed that although the nodes were similar among succession stages, the complexity of networks was significant higher in SF40 than in SC and SF60, suggesting that AMF communities were more active in SF40, which verified the hypothesis of intermediate disturbance hypothesis. This study provides new insights into AMF community dynamics and their driving factors across succession stages, as well as expanding knowledge of the ecological value of AMF for tropical forest restoration processes.

Arbuscular mycorrhizal species vary in their impact on nutrient uptake in sweet corn (Zea mays) and butternut squash (Cucurbita moschata)

An increasing demand for organic produce, coupled with the need to reduce reliance on the diminishing resource of rock phosphate, has bolstered interest in the use of arbuscular mycorrhizae (AMF) as a biofertilizer. AMF are symbiotic fungi that colonize the roots of most crops and transfer nutrients from the soil to their hosts in exchange for carbon. While past studies have shown that mixed AMF communities grown from field soil can increase the yield of many crops, the targeted use of individual AMF species on host plants is a promising avenue to enhance nutrient uptake. We inoculated sweet corn (Zea mays) and butternut squash (Cucurbita moschata) seedlings with nine individual species of AMF and one mixed indigenous population to determine the most beneficial symbionts for enhancing mineral nutrient concentration and yield. Overall, level of root colonization was correlated with phosphorus (P) concentration of aboveground biomass. Corn and squash grown in association with AMF species in the Rhizophagus genus had the highest level of root colonization and tissue P concentration. Claroideoglumus etunicatum and Gigaspora margarita increased calcium (Ca) and magnesium (Mg) concentration in corn and Gigaspora rosea increased calcium in squash. S. constrictum and G. rosea positively impacted sweet corn seedling biomass. Based on this evidence, AMF species vary in their benefit to plant nutrient uptake and the most beneficial species depend on host. Further research on the effectiveness of inoculating individual AMF species across a range of hosts and ecosystems will prove useful in the development of host-targeted AMF biofertilizers.

Mixed conifer-broadleaf trees on arbuscular mycorrhizal and ectomycorrhizal communities in rhizosphere soil of different plantation stands in the temperate zone, Northeast China.

In comparison with ectomycorrhizal (EM) tree species, arbuscular mycorrhizal (AM) trees have different litter quality and nitrogen cycle modes, which may affect mycorrhizal colonization and the community composition and diversity. However, available studies addressing the mycorrhizal fungal colonization rate, diversity and community composition in mixed forest stands composed of AM and EM trees are rare. In the present study, we assessed litter quality, soil physicochemical properties and correlated them with mycorrhizal community characteristics in rhizosphere soils of monoculture and mixture plantation stands of AM tree species (Fraxinus mandschurica Rupr.) and EM tree species (Larix gmelinii Rupr., Picea koraiensis Nakai) in Northeast China. We hypothesized that (1) the effect of mixture pattern on mycorrhizal colonization rate and diversity would change with tree species, (2) the effect of mixture pattern on mycorrhizal community composition would be less pronounced in comparison with that of tree species. We found that mixture did not change AMF colonization rate regardless of mixture identity, whereas mixture and tree species exerted significant effects on EMF colonization rate. For AMF community, both M-AS (Fraxinus mandschurica Rupr. and Picea koraiensis Nakai) and M-AL (Fraxinus mandschurica Rupr. and Larix gmelinii Rupr.) mixtures significantly increased Pielou index and Simpson index, whereas only M-AS significantly increased Sobs. For EMF community, mixture significantly affected examined diversity indices except for Chao1. Mixture significantly shifted AMF and EMF community, and the magnitude was tree species dependent. The dominant genera in AMF and EMF communities in plantation stands were Glomus and Tomentella, respectively. The EnvFit analysis showed that the determinant factors of EMF community are soil moisture, pH, nitrate nitrogen content, dissolved organic nitrogen content, soil organic matter content, soil organic carbon/total nitrogen and litter carbon/total nitrogen. In conclusion, mixed conifer-broadleaf trees significantly changed soil physicochemical properties, litter quality as well as mycorrhizal fungi community diversity and composition.

Arbuscular mycorrhizal fungus communities and their response to soil phosphorous differ between wild and domesticated enset (Ensete ventricosum) in Southern Ethiopia

We tested whether roots from indigenous wild enset in Southern Ethiopia harboured a more diverse and different AMF community compared to cultivated enset. Illumina MiSeq amplicon sequencing showed that AMF communities in both cultivated and wild enset were dominated by Glomeraceae which accounted for 64% of the 145 OTUs recorded. The majority of rare AMF OTUs occurred in cultivated enset, whereas Paraglomeraceae predominated in wild enset roots. AMF richness and diversity were lower in cultivated enset. AMF richness and diversity both in wild and cultivated enset were negatively influenced by available soil P, yet the effect was stronger in communities associated with wild enset. Our results suggest that enset domestication decreased the ability of the crop to associate with a more diverse community of AMF, supporting previous suggestions in other crops regarding reduced AMF diversity.

Distinct effects of host and neighbour tree identity on arbuscular and ectomycorrhizal fungi along a tree diversity gradient

Plant diversity and plant-related ecosystem functions have been important in biodiversity-ecosystem functioning studies. However, biotic interactions with mycorrhizal fungi have been understudied although they are crucial for plant-resource acquisition. Here, we investigated the effects of tree species richness and tree mycorrhizal type on arbuscular (AMF) and ectomycorrhizal fungal (EMF) communities. We aimed to understand how dissimilarities in taxa composition and beta-diversity are related to target trees and neighbours of the same or different mycorrhizal type. We sampled a tree diversity experiment with saplings (~7 years old), where tree species richness (monocultures, 2-species, and 4-species mixtures) and mycorrhizal type were manipulated. AMF and EMF richness significantly increased with increasing tree species richness. AMF richness of mixture plots resembled that of the sum of the respective monocultures, whereas EMF richness of mixture plots was lower compared to the sum of the respective monocultures. Specialisation scores revealed significantly more specialised AMF than EMF suggesting that, in contrast to previous studies, AMF were more specialised, whereas EMF were not. We further found that AMF communities were little driven by the surrounding trees, whereas EMF communities were. Our study revealed drivers of mycorrhizal fungal communities and further highlights the distinct strategies of AMF and EMF.

Reynoutria japonica invasion negatively affects arbuscular mycorrhizal fungi communities regardless of the season and soil conditions

Reynoutria japonica (Japanese knotweed) is one of the most potent global invasive plant species; however, there is still insufficient knowledge on the impact of its invasion on arbuscular mycorrhizal fungi (AMF, Glomeromycota). The aim of our study was to assess the condition of AMF communities under the influence of R. japonica and determine the temporal and site-dependent variability of this influence. We studied AMF spore number, species richness, and composition as well as biomass in pairs of adjacent plots encompassing R. japonica and resident plant species. We established these pairs of plots in different habitat conditions (light and heavier soil conditions), and we sampled them four times (two spring and two summer seasons) to check if the potential impact of the invader on AMF communities is soil- and/or season-dependent. We found that the invasion reduced AMF spore number, species richness, and biomass, but had no effect on AMF species composition. AMF parameters varied over time (spore number, species composition and biomass) and depended on soil condition (species richness), but were barely affected by interactions between the studied factors. The lower performance of AMF communities in R. japonica plots was probably due to the displacement of resident mycorrhizal plant species. This displacement was not complete as some mycorrhizal plants, especially spring ephemerals, managed to survive the invasion. These were probably responsible for the maintenance of AMF communities in the patches of R. japonica. In conclusion, AMF communities are negatively affected by the invasion, but R. japonica does not entirely eliminate AMF, which is optimistic from the viewpoint of restoring sites invaded by this non-mycorrhizal alien plant species.

Soil properties and geography shape arbuscular mycorrhizal fungal communities in black land of China

The black land is a precious strategic soil resource in nature. Arbuscular mycorrhizal fungi (AMF, phylum Glomeromycota) have a critical role in the agricultural ecosystem functioning. However, the black land remains largely unexplored. This study adopted MiSeq sequencing to predict the AMF community distribution and diversities in 41 farmland sites from northeast China's black land. According to findings in this work, all sequences in those 41 soil sites were categorized as one phylum, one class, four orders, eight families, and night genera in the black land of China. Glomus, Paraglomus and Claroideoglomus were the most abundant genera. The diversity of AMF communities was increased with increasing latitude. Moreover, canonical correspondence and pairwise analysis were performed, which suggested that the AMF community structures and diversities were susceptible to latitude, soil organic matter (SOM), soil pH and N. Variance partitioning analysis and Mantel test showed that both soil properties and geographic distance contributed to AMF community structure. It was concluded that the AMF communities showed relatively pronounced diversity at high latitudes, with soil properties and latitude were the important predictors in determining the AMF community structure in the black land of China. Findings in this work shed more lights on the AMF community diversity and distribution and the important factors influencing it at region spatial scale, and suggest that AMF could be used for improving plant growth and sustainable agriculture.

Arbuscular mycorrhizal fungal colonization and soil pH induced by nitrogen and phosphorus additions affects leaf C:N:P stoichiometry in Chinese fir (Cunninghamia lanceolata) forests

The aim of this study was to investigate the mechanisms by which nitrogen (N) and phosphorous (P) additions affect plant C:N:P stoichiometry via changes in AMF communities in a Chinese fir plantation. Experimental plots in a 10-year-old Chinese fir plantation were treated with N addition (LN, 30 kg•ha−1•yr−1, and HN, 60 kg•ha−1•yr−1) and P addition (LP, 20 mg•kg−1, and HP, 40 mg•kg−1) for 2 years starting from 2017. Soil properties, leaf C:N:P stoichiometry, and changes in AMF community composition and diversity were measured. N or P addition increased soil N availability, decreased P availability, and increased N:P in the leaves and soil. Changes in soil pH induced by N and P additions affected the colonization rate and spore density of AMF. AMF colonization rate was increased by N or P addition, and AMF diversity was increased by LN addition. N and P additions altered AMF species composition, and the dominant genus of the AMF in the soil was Glomus in all treatments. The interaction of N and P treatments had no significant effect on AMF diversity. AMF colonization rate and diversity, rather than its composition, affected leaf C:N:P stoichiometry. N and P additions affected colonization rate and diversity of AMF though changes in soil pH, which drove leaf C:N:P stoichiometry, and potentially affected forest productivity via the fungi-soil-plant system.

Diagnose of Indigenous Arbuscular Mycorrhizal Communities Associated to Cynara cardunculus L. var. altilis and var. sylvestris.

Cynara cardunculus L. is a perennial species with high potential for bioenergy production. Arbuscular mycorrhizal symbiosis (AMF) is probably the terrestrial symbiosis most extended on earth. It presence in roots and soils improves plant nutrition and soil quality. Indigenous AMF have developed a variety of modifications to survive in their habitat and thus could serve as potential inoculants for the implantation of plant species in the respective AMF soil habitat. This work aimed to diagnose the status of the AMF symbiosis associated to two cardoon cultivars after a year of growth in a saline soil and in a conventional farming soil. For that purpose we determined AMF parameters in 4 rhizospheric soils and in roots of the cardoon varieties. We found that: (1) the rhizosphere of C. cardunculus var. altilis positively influenced the extraradical mycelium development in the saline soil, (2) the inorganic fertilization history of the conventional farming soil could have had a negative effect on the AMF community and, (3) the intraradical mycelium (IRM) development was extremely low. Our diagnosis suggests that, in order to improve the positive effects of AMF on cardoon growth and soil quality, efforts should be focused on the development of the IRM. In a boarder sense, the implementation of a diagnosis of indigenous AMF communities as a general agronomic practice could become an useful tool to farmers that are willing to potentiate the benefits of AMF on plant growth and soil quality.

Nitrogen‐induced acidification, not N‐nutrient, dominates suppressive N effects on arbuscular mycorrhizal fungi

AbstractArbuscular mycorrhizal fungi (AMF) form symbiosis with most terrestrial plant roots, obtaining photosynthates in return for mineral nutrients. Ecological theories based on the economics of trading partnership predict that nutrient enrichment would suppress AMF. Experimental results from nitrogen (N) and phosphorus (P) additions, however, were highly variable, and the underlying mechanisms remain unclear. Here we show distinct AMF responses to soil N:P stoichiometry manipulations via gradients of long‐term N and P additions in a Mongolian steppe. A complementary experiment with an acid addition gradient was designed to help tease apart the effect of N‐induced acidification from N nutrient. AMF root colonization and extraradical fungal biomass progressively decreased along the P gradient under two distinct host plant species, suggesting a carbon (C)‐P tradeoff. In contrast, low to moderate N inputs increased both AMF parameters, corresponding to the increasing N:P ratio. Yet, high N inputs reduced AMF colonization and biomass, and the magnitudes of N‐led inhibition were similar to those under acid additions that induced comparable changes in soil pH. Structural equation modeling further showed that while soil N:P stoichiometry primarily controlled the effect of P addition on AMF, N‐induced soil acidity overtook the N:P stoichiometry under high N inputs and dominated the effects of reactive N on AMF. In addition, AMF community composition in roots was more dependent on host plants and unresponsive to changes in soil nutrients. We further proposed a comprehensive framework that integrates biological and geochemical effects of reactive N and P inputs on AMF. Together, these results indicate that while the C‐P tradeoff controls P suppression of AMF, N‐induced acidification dominates the N inhibition. Our findings suggest that incorporation of geochemical impacts of N and P inputs would facilitate modeling efforts to project mycorrhizal impact on plant interactions and soil C balance under future nutrient enrichment scenarios.

Contrasting Responses of Rhizosphere Bacteria, Fungi and Arbuscular Mycorrhizal Fungi Along an Elevational Gradient in a Temperate Montane Forest of China.

Elevational gradients strongly affect microbial biodiversity in bulk soil through altering plant and soil properties, but the effects on rhizosphere microbial patterns remain unclear, especially at large spatial scales. We therefore designed an elevational gradient experiment to examine rhizosphere microbial (bacteria, fungi and arbuscular mycorrhizal fungi) diversity and composition using Illumina sequencing of the 16S rRNA and ITS genes for comparison to plant and soil properties. Our results showed that bacterial and fungal alpha diversity was significantly higher at mid-elevation, while AMF alpha diversity decreased monotonically. The beta diversities of the three groups were significantly affected by elevational gradients, but the effect on bacterial beta diversity was larger than on fungal and AMF beta diversity. Proteobacteria, the dominant phyla of bacteria, was significantly higher at the mid-elevation, while Acidobacteria and Actinobacteria significantly decreased as elevation increased. The main fungal taxa, Basidiomycota, significantly decreased with elevation, and Ascomycota significantly increased with elevation. Glomeromycota, the dominant AMF phyla, responded insignificantly to the elevational gradients. The responses of bacterial and fungal alpha diversity were mostly associated with tree diversity and organic carbon, whereas AMF alpha diversity mainly depended on litter N and P. Changes in bacterial community composition along the elevational gradient were explained primarily by litter N and P, and litter P was the main driver of fungal and AMF community composition. Overall, our results suggest that plant litter, particularly litter N and P, were the main source of external carbon input and drove the observed differences in rhizosphere microbial diversity and community composition. Our results highlight the importance of litter nutrition in structuring rhizosphere microbial communities in mountain ecosystems.