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Both indigenous arbuscular mycorrhizal (AM) fungi and phosphate solubilizing bacteria (PSB) are involved in phosphorus (P) mobilization and turnover in agroecosystems. Understanding the diversity and community structure of AM fungi and PSB is important for potentially optimizing their role in mining P for sustainable agriculture. Yet the characteristics of both AM fungi and PSB in response to P input, in particular the influence of different indigenous microbial communities on plant growth has been little studied. Here, we collected soil samples from the top 20 cm of the profile of a soil receiving three fertilizer P rates, comprising nil, optimal (44 kg P ha −1 ) and excessive (131 kg P ha −1 ) P to evaluate the AM fungal community structure and abundance of relevant PSB groups at three sampling times (June, July and September) using 454 pyrosequencing and quantitative-PCR (q-PCR), respectively. In addition, a pot experiment was conducted to investigate the feedback effects of different fractions of indigenous soil microbes on maize seedling growth. The results showed that overall sampling time had a greater impact than P application rate on the community structure of AM fungi and PSB abundance. At each sampling time the AM fungal communities were significantly affected by the fertilizer P rate. The overall abundance of soil microbes and selected taxa were slightly affected by sampling time but not by fertilizer P. Shoot biomass and P nutrition were significantly affected by the microbial community fraction but not by the fertilizer P rate. Changes in AM fungal communities did not lead to significant differences in maize growth. However, long-term absence of P inputs tended to build up microbial communities which greatly suppressed maize growth. Shoot biomass showed a mean decline of 24.4% when grown in inoculated soil compared to sterilized soil. Our results indicate that current P management has not led to negative influences on soil microbial communities. Evidence highlights the need to understand the interactions between plants and microbiome in mining P in order to make maximum use of the most effective indigenous soil microbes for sustainable agriculture. [ABSTRACT FROM AUTHOR]

Background and aims: Overyielding in intercropping compared to monoculture has been widely reported. One of the mechanisms may be the alteration of the microbial community in intercropping and especially the amelioration of the negative effects of pathogens that can accumulate in monocultures. Here we test whether inoculation with arbuscular mycorrhizal fungi (AMF) and wheat take-all disease influences overyielding and whether changes in the microbial communities generate feedbacks on plant growth. Methods: In Experiment 1, wheat and faba bean were grown in monoculture or intercropping to form three planting patterns. Plants were inoculated with or without wheat take-all disease ( Gaeumannomyces graminis), and one, six, or no AM fungi, to create 6 soil conditioned treatments. Soils from Experiment 1 were used as inocula in Experiment 2 to test the feedback on plant growth from monocultures and the legacy benefits of intercropping. Results: No significant influence of AMF on plant growth was observed in either experiment. In Experiment 1, AMF had no significant effect in suppressing take-all but take-all tended to decrease AMF colonization. Shoot biomass and competitive ability of wheat was suppressed by take-all in both experiments. Wheat and faba bean showed overyielding in both the take-all and non-take-all treatment in Experiment 1 but only overyielding in the take-all treatment in Experiment 2. Growth of wheat and faba bean were suppressed in conspecific soil, and this negative feedback was observed across all take-all and AMF treatments, and regardless of competition. Biomass of wheat and faba bean was higher in soil from intercropping than in monoculture soil, and this positive legacy benefit of intercropping did not depend on take-all, AMF or plant competition. Conclusions: We find support for alterations of the soil community causing negative plant soil feedback and positive legacy benefits of intercropping. Our results are consistent with microbial dynamics generating overyielding in intercropping by reducing the negative influence of soil pathogen build-up on conspecific host plants and simultaneously compensatively improving growth of neighbor plants. [ABSTRACT FROM AUTHOR]

Foraging strategies in arbuscular mycorrhizal fungi (AMF) for heterogeneously distributed resources in the soil remain to be explored. We used nylon-mesh bags of 30 μm to simulate patches of different phosphorus (P) supply levels (Expt 1) and P forms (organic υ. inorganic, Expts 1 and 2). In Expt 1, host maize (Zea mays) was unfertilised; in each pot, five P-enriched bags were supplied with either Na-phytate or KH2PO4 at P rates of 0 (P0), 50 (P50), 100 (P100), 150 (P150) and 200 (P200) mg P kg-1. In Expt 2, maize plants were supplied with 20 (P20) or 50 (P50) mg P kg-1, and five P-enriched bags were supplied with different P forms (Na-phytate, lecithin, RNA, KH2PO4) and a nil-P control. Three fungal species (Funneliformis mosseae, Rhizophagus irregularis, and Glomus etunicatum) were compared in Expt 1, and the first two species in Expt 2. In Expt 1, the hyphal-length density (HLD) of G. etunicatum was not significantly different among different P levels when supplied with KH2PO4, whereas theHLDof R. irregularis tended to increase at higherPsupply (above P50) in the Na-phytate treatment. TheHLDof F. mosseae increased at P150 when supplied with KH2PO4, and increased at P100 and P150 in the Naphytate treatment relative to P0. APase activity levels were more related to P supply level, in particular with F. mosseae inoculation and uninoculated control, showing that P200 significantly reduced APase relative to P0. In Expt 2, greater hyphal growth of both fungal species tended to occur with KH2PO4. At P20, the HLD of R. irregularis in treatments with KH2PO4 and lecithin, and of F. mosseae with KH2PO4, were higher than in P0. At P50, the HLD of F. mosseae was higher than of R. irregularis; but P form had no significant influence on HLD of F. mosseae, whereas the HLD of R. irregularis in the P-amended treatment (except with Na-phytate) was higher than in P0. APase activity did not differ significantly between the two fungal species. Highest APase activity generally occurred with lecithin, with no significant difference among the other P forms. Our results indicate that the response of AMF to P-enriched patches is complex, and both the form and amount of P supplied should be considered. Variations between AMF in the proliferation of hyphae to heterogeneous nutrient patches might be a mechanism by which these species can maintain diversity in intensive agricultural ecosystems. [ABSTRACT FROM AUTHOR]

BACKGROUND: Maintaining or improving soil chemical quality is critical for sustainable agricultural productivity and environmental safeguards. Organic fertilizer application, a common agricultural practice in banana cultivation, is often associated with greater microbial biomass and activity, which are linked to improvements in soil chemical quality. However, the effect of the duration of organic fertilizer application on soil chemical quality and whether it is microbially driven still needs to be investigated. We collected soil samples from banana plantations consistently applying organic fertilizers for 1 (Y1), 4 (Y4), 7 (Y7) and 10 (Y10) years. Soil chemical quality is expressed as total data set (TDS) and minimum data set (MDS) based on chemical indicators, and soil microorganisms are characterized by phospholipid fatty acid (PLFA). RESULTS: Based on TDS and MDS, the soil chemical quality indices in Y7 and Y10 treatments were significantly higher than that in Y1 and Y4 treatments. Soil total PLFA concentrations and the proportional abundance of fungi and arbuscular mycorrhizal fungi increased with prolonged banana cultivation. Total PLFA concentrations were significantly positive correlation with the soil chemical quality index. Soil gram‐positive bacteria (G+), bacteria, protozoa and ratio of G+ to gram‐negative bacteria (G–) were major drivers of soil chemical quality. CONCLUSION: The organic fertilizer application can significantly improve soil chemical quality, which is regulated by soil bacteria. Regular application of organic fertilizers is important in promoting soil quality and soil biological properties need to be incorporated into the assessment of soil health in banana plantations. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) play an important role in crop productivity, but their response to different fertilization regimes is variable. Understanding the mechanisms governing mycorrhizal responses under various fertilization regimes is key to maximizing the mycorrhizal contribution to ecosystem functioning. Indigenous AMF communities and soil were collected from long-term field experiments with various fertilization regimes. A greenhouse bioassay was carried out to identify the key regulators of the mycorrhizal response to inorganic and organic fertilization. Different fertilization regimes generated continuous gradients for most soil properties and a full spectrum of mycorrhizal phenotypes. Mycorrhizal growth response (MGR) in particular showed complex shifts from positive to neutral to negative, while mycorrhizal phosphorus (P) response was consistently positive and mycorrhizal nitrogen (N) response was consistently negative in fertilized treatments. Soil available P and available N to P (N:P) ratio appeared to be key soil predictors of the mycorrhizal response. Also, the nutrient status of non-mycorrhizal (NM) plants, namely shoot N concentration, shoot P concentration and shoot N:P ratio, were plant predictors of mycorrhizal response. A positive MGR occurred when NM plants were P-limited, and neutral and negative MGR occurred when NM plants were N-limited or co-limited by N and P. Further, the thresholds of soil available P (c. 13 mg kg-1), NM shoot N concentration (c. 14 g kg-1), NM shoot P concentration (c. 0.7 g kg-1) and NM shoot N:P ratio (c. 18), respectively, were estimated to predict mycorrhizal response. We conclude that the relative availability of N and P in soil and NM plants are good predictors of mycorrhizal response in different fertilization regimes. The existing nutrient thresholds combining soil and plant allowed more accurate prediction of mycorrhizal response and this has important implications for optimizing the mycorrhizal association in some important crops by managing soil nutrients. • A wide spectrum of mycorrhizal phenotypes was observed in multiple fertilization regimes. • Soil P availability and N:P ratio were key soil predictors of mycorrhizal response. • N and P status of non-mycorrhizal plants were key plant predictors of mycorrhizal response. • Nutrient thresholds in soil and plants in predicting mycorrhizal response were identified. [ABSTRACT FROM AUTHOR]

• Drought stress affected soybean growth and physiology. • Leaf temperature reflected the effect of AMF on plant water status under drought stress. • AMF regulated leaf temperature to affect other physiological activities. The influence of arbuscular mycorrhizal fungi (AMF) on plant water status and growth under drought stress were investigated using soybean subjected to drought stress (40% of soil water-holding capacity (WHC)) and control conditions (60% WHC) either inoculated with AMF or uninoculated controls. Leaf temperature (T leaf) and stomatal conductance (gs) were determined at 10:00, 12:00 and 18:00 on the harvest day. The effects of AMF on the water physiological status and growth of soybeans under drought stress were examined using thermal infrared imaging technology (TIIT). AMF inoculation under drought stress increased plant above- and below-ground biomass, nutritional status, and nitrogen, phosphorus and potassium uptake rates, and reduced plant root/shoot ratio. Monitoring T leaf reflected the effect of AMF on plant water physiological status under drought stress. AMF inoculation resulted in a decline in T leaf of 0.1–0.4 °C as water uptake proceeded compared with an increase of 0.2–1.4 °C in uninoculated controls. Thus, the effects of AMF on soybean drought resistance changed from positive to negative. AMF reduced plant T leaf , promoted the accumulation of photosynthetic products, reduced malondialdehyde accumulation, and increased stomatal regulation and T leaf. These preliminary results provide a basis for further studies on the effects of AMF on the water and growth status of plants under drought stress in arid areas. [ABSTRACT FROM AUTHOR]

Thermal infrared imaging technology was used to understand the effects of arbuscular mycorrhizal fungi (AMF) and dark septate endophytic (DSE) fungi, both separately and together, on plant growth and physiological status, and to screen and develop efficient microbial agents in a pot experiment design. Eight treatments comprised the control (CK), AMF inoculation alone, DSE fungal treatments (DSE20%, DSE40% and DSE80%; 2, 4, 8 × 105 CFU mL−1) and combined inoculation treatments (DSE20% + AMF, DSE40% + AMF, and DSE80% + AMF). Canopy temperature (Tcanopy) and stomatal conductance (gs) were monitored at different growth stages, and plant biomass-related indicators were obtained at harvest. These indicators were used to assess plant growth and the physiological status resulting from the different inoculation treatments. During plant growth, the plant Tcanopy decreased following inoculation. Differences in Tcanopy between control and inoculated plants were detected by thermal infrared imaging technology and were −3.8 to + 9.3 °C (control–inoculation treatment). Growth index and Tcanopy monitoring indicate that the growth-promoting effect of combined inoculation was higher than that of either fungal type alone, with DSE80% + AMF producing the highest growth promotion. During the growth process of inoculated maize, the effect of inoculated AMF on the physiological condition of maize growth can be better monitored by thermal infrared at 10 a.m., 12 p.m., 2 p.m. and 4 p.m. on the 31st–57th days of the growth period. The method and results of this experiment are conducive to the rapid and efficient monitoring of the effects of microorganisms on plant growth and physiological status and can be applied to the screening, application, and promotion of microbial agents. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) fungi contribute to the revegetation of degraded ecosystems such as coal mining areas and may indirectly affect the development of biological soil crusts (biocrusts). However, bacterial diversity and microbial nutrient cycling in the soil underlying biocrusts are seldom considered when assessing ecological restoration effects. Bacterial community composition was quantified and compared using 16S rRNA gene sequencing, metabolic limitation of microbes via extracellular enzymatic stoichiometry and their association with carbon use efficiency (CUE) in soil underlying moss biocrusts in vegetated areas inoculated with an AM fungus or uninoculated and in uninoculated unvegetated areas. The AM fungal inoculum significantly influenced bacterial community composition and diversity, extracellular enzyme activities and CUE in soil underlying moss biocrusts mainly by affecting soil nutrients. Correlation analysis revealed that Actinobacteria, Armatimonadetes, Bacteroidetes, Chlorobi, Cyanobacteria, Saccharibacteria, and Verrucomicrobia were positively correlated with soil nutrients carbon (C), nitrogen (N) and phosphorus (P). A vector analysis of extracellular enzyme activity indicates that soil microbial communities underlying moss biocrusts were limited by P but microbial communities in areas inoculated with the AM fungus had the lowest relative P limitation. The alleviation of microbial P limitation increased the microbial CUE and bacterial phylum community and alpha diversity, leading to an increase in subsoil C content underlying moss biocrusts. This indicates that microbial communities in soil underlying moss biocrusts under in restoration areas containing the AM fungus were more stable under environmental stress, and the inclusion of AM fungal inoculation may be recommended as the preferred option for ecosystem restoration in arid and semi-arid coal mining areas. • Soil microbial communities under moss biocrusts were P-limited. • AM fungal inoculum increased microbial CUE and bacterial biodiversity under biocrusts. • Microbial P limitation was minimum in areas inoculated with the AM fungus. • More diverse soil bacterial communities had higher microbial CUE values. [ABSTRACT FROM AUTHOR]

Summary: Hotspots of N2O emissions are generated from legume residues during decomposition. Arbuscular mycorrhizal fungi (AMF) from co‐cultivated intercropped plants may proliferate into the microsites and interact with soil microbes to reduce N2O emissions. Yet, the mechanisms by which or how mycorrhizal hyphae affect nitrifiers and denitrifiers in the legume residues remain ambiguous. Here, a split‐microcosm experiment was conducted to assess hyphae of Rhizophagus aggregatus from neighbouring maize on overall N2O emissions from stubbles of nodulated or non‐nodulated soybean. Soil microbes from fields intercropped with maize/soybean amended with fertilizer nitrogen (SS‐N1) or unamended (SS‐N0) were added to the soybean chamber only. AMF hyphae consistently reduced N2O emissions by 20.8%–61.5%. Generally, AMF hyphae promoted the abundance of N2O‐consuming (nosZ‐type) denitrifiers and altered their community composition. The effects were partly associated with increasing MBC and DOC. By contrast, AMF reduced the abundance of nirK‐type denitrifiers in the nodulated SS‐N0 treatment only and that of AOB in the non‐nodulated SS‐N1 treatment. Taken together, our results show that AMF reduced N2O emissions from soybean stubbles, mainly through the promotion of N2O‐consuming denitrifiers. This holds promise for mitigating N2O emissions by manipulating the efficacious AMF and their associated microbes in cereal/legume intercropping systems. [ABSTRACT FROM AUTHOR]

A pot experiment was carried out to investigate the tolerance of cucumber plants (Cucumis sativus L.) to root-knot nematode after inoculation with Glomus intraradices. Plants were inoculated with G. intraradices for four weeks and then transplanted in soil treated with Meloidogyne incognita for a further five weeks. The low phosphorus (P) loamy soil was amended with 50 and 100 mg P kg-1 soil. Mycorrhizal colonization increased shoot dry weight, shoot length, leaf numbers, root fresh weight and shoot P concentration, whereas nematode penetration and reproduction were significantly decreased. Similarly, P fertilization usually increased shoot growth and significantly decreased the number of galls and the number of egg masses and eggs per g root. Our results indicate that inoculation with G. intraradices and P fertilizer confer tolerance of cucumber plants to M. incognita by enhancing plant growth and by suppressing reproduction and/or galling of nematodes during the early stages of plant growth. [ABSTRACT FROM AUTHOR]

Abstract: The effects of arbuscular mycorrhizal (AM) fungus (Glomus mosseae) and phosphorus (P) addition (100 mg/kg soil) on arsenic (As) uptake by maize plants (Zea mays L.) from an As-contaminated soil were examined in a glasshouse experiment. Non-mycorrhizal and zero-P addition controls were included. Plant biomass and concentrations and uptake of As, P, and other nutrients, AM colonization, root lengths, and hyphal length densities were determined. The results indicated that addition of P significantly inhibited root colonization and development of extraradical mycelium. Root length and dry weight both increased markedly with mycorrhizal colonization under the zero-P treatments, but shoot and root biomass of AM plants was depressed by P application. AM fungal inoculation decreased shoot As concentrations when no P was added, and shoot and root As concentrations of AM plants increased 2.6 and 1.4 times with P addition, respectively. Shoot and root uptake of P, Mn, Cu, and Zn increased, but shoot Fe uptake decreased by 44.6%, with inoculation, when P was added. P addition reduced shoot P, Fe, Mn, Cu, and Zn uptake of AM plants, but increased root Fe and Mn uptake of the nonmycorrhizal ones. AM colonization therefore appeared to enhance plant tolerance to As in low P soil, and have some potential for the phytostabilization of As-contaminated soil, however, P application may introduce additional environmental risk by increasing soil As mobility. [Copyright &y& Elsevier]

Background: Effects on maize were assessed of dual inoculation with arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) isolated from other plant species. Methods: Suspensions of DSE isolated from Stipa krylovii were prepared at different densities (2, 4, and 8 × 105 CFU mL− 1) and inoculated separately (AMF or DSE) or together (AMF + DSE), to explore their effects on maize growth. Results: Inoculation with AMF or medium and high densities of DSE and combined inoculation (AMF + DSE) increased plant above-ground growth and altered root morphology. Differences in plant growth were attributable to differences in DSE density, with negative DSE inoculation responsiveness at low density. AMF promoted plant above-ground growth more than DSE and the high density of DSE promoted root development more than AMF. Combined inoculation might lead to synergistic growth effects on maize at low density of DSE and competitive effects at medium and high DSE densities. Conclusions: AMF and DSE co-colonized maize roots and they had positive effects on the host plants depending on DSE density. These findings indicate the optimum maize growth-promoting combination of AMF and DSE density and provide a foundation for further exploration of potentially synergistic mechanisms between AMF and DSE in physiological and ecological effects on host plants. [ABSTRACT FROM AUTHOR]

Summary: Arbuscular mycorrhizal fungi (AMF) play an important role in maintaining plant diversity and productivity in grassland ecosystems. However, very few studies have investigated how AMF and plant communities co‐vary between contrasting environments in natural ecosystems. Intensive sampling (50 soil samples) was conducted in natural open grasslands at both 3570 and 4556 m on Mount Segrila on the Southeast Tibetan Plateau. We used 454‐pyrosequencing to investigate soil AMF communities and to explore relationships between AMF diversity and plant richness, productivity and community composition. AMF diversity was negatively correlated with plant richness at 3570 m but positively at 4556 m. Differences in AMF community composition between elevations were attributable to plant community composition, soil pH and available phosphorus concentration. The AMF community was more phylogenetically clustered at the higher elevation than the lower elevation. However, greater phylogenetic clustering (under dispersion) of AMF communities at the two elevations was positively correlated with above‐ground biomass. Our results indicate that plant community composition and environmental filtering are the primary drivers structuring the AMF community. Phylogenetic relatedness may be important in explaining the function of AMF communities in alpine ecosystems. [ABSTRACT FROM AUTHOR]

Summary: Recent work demonstrates that habitat conditions exert striking effects on symbiont performance by mediating trade‐offs in plants, AM fungi and environmental interactions. However, how local temperature conditions influence the functional diversity of mycorrhizal symbioses and the genetics of coexisting AM fungi at the local scale remain unclear. In the present study, we conducted a reciprocal inoculation experiment to explore the performance of sympatric associations against allopatric associations under contrasting temperatures and the AM fungal community in colonized roots. No local adaptation of plant biomass was found under both temperature conditions investigated, but a consistent local versus foreign effect was found in AM fungal performance. The temperature and the origin of the inoculum relative to the plant origin were important in explaining symbiotic function. Correspondingly, the community structure and Nearest Relatedness Index of the AM fungal community of the root symbiont varied with inoculum source, and assemblages with more closely related taxa led to a decline in plant biomass and stronger disequilibrium among AM fungi in roots. Our findings suggest that functional divergence exists in naturally coexisting communities of AM fungi from contrasting climatic origins, and fungal relatedness is an important driver of plant growth. [ABSTRACT FROM AUTHOR]

Variation in the symbiotic function of arbuscular mycorrhizal fungi (AM fungi) has been demonstrated among distinct biotic and abiotic interactions. However, there is little knowledge on how local temperature conditions influence the functional divergence of AM symbionts in alpine ecosystems. Here, we conduct a reciprocal inoculation experiment to explore the three-way interactions among plants, AM fungal inoculum and temperature at sites of contrasting elevation. Evidence of local adaptation of plant growth was found only under low temperature conditions, with no consistent local versus foreign effect found in AM fungal performance. The origin of either the plant or the inoculum relative to the temperature was important in explaining symbiotic function. Specifically, when inoculum and temperature were sympatric but allopatric to the plant, poor adaptation by the plant to the novel environment was clearly found under both temperature conditions. Further analysis found that the symbiotic function was inversely related to fungal diversity under high temperature conditions. These results suggest that local adaptation represents a powerful factor in the establishment of novel combinations of plant, inoculum and temperature, and confirms the importance of taking into account both biotic and abiotic interactions in the prediction of the response of symbionts to global environmental change. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) fungi form potentially symbiotic associations with most crop species and potentially increase crop phosphorus (P) uptake in intensive cropping systems. Their widespread use, however, remains restrained by our limited understanding of the processes that determine the outcome of the associations. Here, we have used 32P to quantify the delivery of P to maize (Zea mays L.) and wheat (Triticum aestivum L.) via indigenous AM fungi in compartmented pots under high- and low-P conditions. Soil P level was important in driving shoot P uptake via the direct root pathway (DP) or the mycorrhizal pathway (MP). The MP contribution reached 81.8 and 75.8%, respectively, in maize and wheat at low P status but declined to 40.6 and 9.1% at high P. The abundance of intraradical and extraradical colonization and the relative abundance of Rhizophagus and shoot P utilization efficiency (PUE) significantly impacted the MP contribution. Larger mycorrhizal P and growth responses were closely related to a higher MP contribution and shoot PUE in maize but only P response was significantly related to the latter in wheat. These results suggest that crops can acquire considerable amounts of P via the MP with indigenous AM fungi, especially at low P levels, and highlight the importance of plant and AM fungal identity in regulating the relationship between hidden P uptake and symbiotic outcomes. Therefore, manipulation of fertilizer P application rates to optimize the abundance and assemblage of the indigenous AM fungi and crop PUE to increase MP activity and symbiotic outcomes may contribute to the efficient utilization of AM fungi in intensive cropping systems. • Crops took up considerable amounts of P via AM fungi but were regulated by P level. • AMF colonization, Rhizophagus abundance and shoot PUE affected the MP contribution. • The relationship between MP contribution and MGR differed between maize and wheat. [ABSTRACT FROM AUTHOR]

The diversity of arbuscular mycorrhizal fungi ( AMF) in sedges on the Tibetan Plateau remains largely unexplored, and their contribution to soil aggregation can be important in understanding the ecological function of AMF in alpine ecosystems. Roots of K obresia pygmaea C. B. Clarke and C arex pseudofoetida Kük. in alpine K obresia pastures along an elevational transect (4149-5033 m) on Mount Mila were analysed for AMF diversity. A structural equation model was built to explore the contribution of biotic factors to soil aggregation. Sedges harboured abundant AMF communities covering seven families and some operational taxonomic units are habitat specific. The two plant species hosted similar AMF communities at most altitudes. The relative abundance of the two sedges contributed largely to soil macroaggregates, followed by extraradical mycorrhizal hyphae ( EMH) and total glomalin-related soil protein ( T-GRSP). The influence of plant richness was mainly due to its indirect influence on T-GRSP and EMH. There was a strong positive correlation between GRSP and soil total carbon and nitrogen. Our results indicate that mycorrhization might not be a major trait leading to niche differentiation of the two co-occurring sedge species. However, AMF contribute to soil aggregation and thus may have the potential to greatly influence C and N cycling in alpine grasslands. [ABSTRACT FROM AUTHOR]

Plant community productivity and species composition are primarily constrained by water followed by nitrogen ( N) availability in the degraded semi-arid grasslands of Inner Mongolia. However, there is a lack of knowledge on how long-term N addition and water availability interact to influence the community structure of arbuscular mycorrhizal ( AM) fungi, and whether AM fungi contribute to the recovery of degraded grasslands. Soils and roots of the dominant plant species S tipa grandis and A gropyron cristatum were sampled under two water levels and N) rates after 8 years. The abundance and diversity of AM fungi remained relatively resilient after the long-term addition of water and N. Variation in the AM fungal communities in soils and roots were affected primarily by watering. AM fungal abundance and operational taxonomic unit ( OTU) richness were significantly correlated with average aboveground net primary productivity and biomass of plant functional groups. Hyphal length density was significantly correlated with plant richness, the average biomass of S . grandis and perennial forbs. Both water and plant biomass had a considerable influence on the AM fungal assemblages. The tight linkages between AM fungi with aboveground plant productivity highlight the importance of plant-microbe interactions in the productivity and sustainability of these semi-arid grassland ecosystems. [ABSTRACT FROM AUTHOR]

A better understanding of Glomeromycotan biogeography is essential for the conservation of arbuscular mycorrhizal (AM) fungal species and the ecosystem services that they provide worldwide. Here, we examine the spatial dynamics of AM fungi along two slopes (4149 m a.s.l. to the summit at 5033 m a.s.l.) of Mount Mila on the Tibetan Plateau. Our hypothesis was that AM fungal communities at higher elevation would show distinct assemblages with lower diversity in conditions of increasing environmental harshness. A total of 52 operational taxonomic units (OTUs) spanning all four orders were detected and some OTUs were habitat specific. Nearly 30% of the OTUs were new phylotypes, including two family-like clades. Distinct communities of AM fungi were found at the higher elevation, demonstrating potential niche differentiation along the elevation gradient. Elevation patterns of taxon richness/diversity differed between the two transects, decreasing with increasing elevation on the eastern slope and unimodal (or no pattern) on the western slope. Taken together, we provide evidence for significant spatial structure of AM fungi across the elevation gradient, and the distribution patterns are regulated simultaneously by the plant communities, soil properties and climatic conditions in this plateau montane ecosystem. [ABSTRACT FROM AUTHOR]

Background and aims: The foraging capability of extraradical mycelium (ERM) of arbuscular mycorrhizal (AM) fungi to high soil phosphorus (P) supply and carry-over effect of ERM on new host plants remain to be explored. This study investigated whether the inhibition of ERM at high P supply varies between fungal species and whether ERM have carry-over effects when they encounter new hosts. Methods: A two-compartment device was designed to spatially separate hyphae from host roots and the carry-over effect was investigated using two-stage growth experiments. P fertilizers were applied only to hyphal compartments at a gradient of 0, 35, 150, 300, or 1,000 mg P∙kg. Maize plants were inoculated with Glomus mosseae, Rhizophagus irregularis or remained uninoculated. Results: The biomass of G. mosseae in the hyphal compartment was on average higher than that of R. irregularis and the difference was greater at the second harvest. The biomass of G. mosseae increased slightly at P35 and thereafter decreased significantly with increasing P level. The biomass of R. irregularis increased slightly at P35 and did not differ significantly at higher P levels from that at P0. In general, inoculation significantly increased the biomass and P uptake of donor and receiver plants. The mycorrhizal growth responsiveness (MGR) and mycorrhizal phosphorus responsiveness (MPR) of both donor and receiver plants decreased at higher P supply level. The ratios of MGR and MPR between donor and receiver plants were close to 1 for both fungal species and were independent of P level. Inoculation with R. irregularis significantly enhanced root P uptake efficiency and alkaline phosphatase activity (ALP) in both donor and receiver plants across all P levels. Conclusions: Our results demonstrate that fungal species differ in their responses to soil P availability. R. irregularis was less sensitive to soil P gradients, and compensated for growth promotion and P uptake of the host by increasing ALP and root P uptake efficiency. The carry-over effects of ERM imply that the maintenance of mycorrhizal networks is of particular importance in intensive agricultural ecosystems. [ABSTRACT FROM AUTHOR]

Appropriate nitrogen (N) management is important to minimize N losses from intensively managed agricultural ecosystems. Understanding the community structure of arbuscular mycorrhizal fungi ( AMF) in response to N management can be of great ecological significance, particularly with the recent emphasis on the role of AMF in N cycling. A comprehensive study of both the vertical distribution of AMF in the soil profile and the temporal changes in community structure in maize roots was conducted over a 5-year period at a field site on the North China Plain. The N treatments consisted of zero N, conventional farming practice, and optimum N based on an in-season soil Nmin test. Terminal restriction fragment length polymorphism and clone sequencing were used to analyse the AMF community. Optimum N mitigated the decline in richness of AMF in the conventional N treatment in the surface soil. Diverse and species-rich AMF communities occurred deep in the soil profile. A significant difference in AMF community structure was observed between the control and fertilizer N treatments but not between the two N application strategies. AMF communities deeper in the soil profile were subsets of those richer communities in the surface soil and the loss of AMF taxa was mostly due to the absence of rare taxa. Soil pH and Nmin contents were major soil properties affecting the soil AMF communities among the N treatments while vertical distribution was influenced mainly by soil electrical conductivity. Crop phenology had a stronger influence than N treatment on the temporal shifts in AMF communities in maize roots. Our results provide evidence for the importance of N management in maintaining AMF diversity. Changes in soil chemical properties due to N fertilization, in particular declining soil pH, should be integrated in N management strategies to reduce the negative impacts on AMF communities induced by N fertilization. Excessive N inputs induced significant changes in soil physicochemical properties, especially soil acidification, and may have negative impacts on AMF communities. [ABSTRACT FROM AUTHOR]

A modified in-growth core technique was employed to determine the contribution of indigenous arbuscular mycorrhizal fungi (AMF) to plant growth and nutrient uptake in intensive agroecosystems at two Experimental field sites at Shangzhuang (Experiment I) and Quzhou (Experiment II) in North China. The growth cores (26.5 cm depth, 5 cm diameter for maize plants, and 4 cm for alfalfa and tomato plants) were covered with 40-μm nylon mesh (restriction of hyphal growth) and buried in the soil. They either remained static (static mesh) or were regularly rotated (rotated mesh) to disrupt hyphal penetration into the cores. A non-rotated 0.45-μm mesh (block mesh, inhibition of hyphal growth) treatment which remained static was also included to compare with the rotated mesh treatment (Experiment I). Growth cores from the two experimental sites had different soil types and two contrasting low P levels. The soil in the growth cores was sieved and sterilized before being placed into the growth core. Three plant species, namely maize, tomato and alfalfa were selected. The growth periods for maize plants were 35 days (Experiment I) and 39 days (Experiment II), respectively, and the corresponding growth periods for tomato and alfalfa were 67 days (Experiment I) and 53 days (Experiment II). At harvest the AMF species inside and outside the in-growth cores were identified by polymerase chain reaction (PCR), cloning and sequencing. Irrespective of plant species or genotype (maize), root colonization rates and hyphal length density (Experiment I) were generally suppressed in the rotated mesh treatment. The inhibition of hyphal growth by block mesh was comparable to that by the rotated mesh treatment. The growth of all three plant species in static mesh at the two Experimental sites, at both low (Experiment I) and sub-optimal soil P supply levels (Experiment II), was significantly higher than in the rotated (or block mesh) treatment. Root colonization rates of three maize genotypes were positively correlated with plant P concentration (Experiment II). Uptake efficiencies of P and N were significantly higher in static mesh than in the rotated (or block) treatment. AMF species detected (Experiment I) were all Glomerales, including the genera Glomus and Rhizophagus. One identified species of Rhizophagus intraradices and one Glomus viscosum-like phylotype were the dominant species. We conclude that the indigenous AM are crucial for early seedling growth, particularly for plants with small seeds and low P reserves and when seedlings exhibit P deficiency. The facilitation effect is highly relevant to enhanced root P (and possibly N) uptake and P delivery by the fungal mycelium. Our results have implications for the importance of maintenance of intact hyphal networks in intensive agroecosystems. [ABSTRACT FROM AUTHOR]

A field experiment was conducted to study the effects of inoculation with the arbuscular mycorrhizal fungus Glomus caledonium and/or Rhizobium meliloti on phytoremediation of an agricultural soil contaminated with weathered PCBs by alfalfa grown for 180 days. Planting alfalfa (P), alfalfa inoculated with G. caledonium (P+AM), alfalfa inoculated with R. meliloti (P+R), and alfalfa co-inoculated with R. meliloti and G. caledonium (P+AM+R) decreased significantly initial soil PCB concentrations by 8.1, 12.0, 33.8, and 43.5%, respectively. Inoculation with R. meliloti and/or G. caledonium (P+AM+R) increased the yield of alfalfa, and the accumulation of PCBs in the shoots. Soil microbial counts and the carbon utilization ability of the soil microbial community increased when alfalfa was inoculated with R. meliloti and/or G. caledonium. Results of this field study suggest that synergistic interactions between AMF and Rhizobium may have great potential to enhance phytoremediation by alfalfa of an agricultural soil contaminated with weathered PCBs. [ABSTRACT FROM AUTHOR]

Abstract: The effects of an arbuscular mycorrhizal (AM) fungus (Glomus etunicatum) on atrazine dissipation, soil phosphatase and dehydrogenase activities and soil microbial community structure were investigated. A compartmented side-arm (‘cross-pot’) system was used for plant cultivation. Maize was cultivated in the main root compartment and atrazine-contaminated soil was added to the side-arms and between them 650 or 37μm nylon mesh was inserted which allowed mycorrhizal roots or extraradical mycelium to access atrazine in soil in the side-arms. Mycorrhizal roots and extraradical mycelium increased the degradation of atrazine in soil and modified the soil enzyme activities and total soil phospholipid fatty acids (PLFAs). Atrazine declined more and there was greater stimulation of phosphatase and dehydrogenase activities and total PLFAs in soil in the extraradical mycelium compartment than in the mycorrhizal root compartment when the atrazine addition rate to soil was 5.0mg kg−1. Mycelium had a more important influence than mycorrhizal roots on atrazine degradation. However, when the atrazine addition rate was 50.0mg kg−1, atrazine declined more in the mycorrhizal root compartment than in the extraradical mycelium compartment, perhaps due to inhibition of bacterial activity and higher toxicity to AM mycelium by atrazine at higher concentration. Soil PLFA profiles indicated that the AM fungus exerted a pronounced effect on soil microbial community structure. [Copyright &y& Elsevier]

• Ground fissures altered root system spatial distribution and endogenous hormone levels. • Mycorrhiza increased fine root percentage in root-damaged plants. • Mycorrhiza may change damaged root system morphology by regulating hormone levels. Ground subsidence caused by coal mining can produce large amounts of surface ground fissures which may damage the surrounding plant roots. Here, a device was used that simulates root damage and we observed the growth of maize roots in real time, the morphological responses of roots and leaves to fissure-induced root damage stress, and the effects of arbuscular mycorrhizal fungi (AMF). Time series of root and leaf growth and hormonal changes in mycorrhizal and control plants with damaged root systems were observed for the first time. Indole-3-acetic acid (IAA) and cytokinin (CTK) levels in roots and leaves decreased significantly one week after ground fissuring. Abscisic acid (ABA) levels increased and the growth of roots and leaves was inhibited. Arbuscular mycorrhizal fungi (AMF) reversed these trends and significantly increased the percentages of root tips and fine roots compared with uninoculated controls. IAA and CTK levels declined significantly in roots and leaves six weeks after ground fissuring but ABA levels remained unchanged. AMF inoculation significantly increased both IAA and CTK levels but decreased ABA levels. The spatial distribution of roots was affected by fissures in addition to the changes in hormones. The negative impacts of ground fissures on maize growth were alleviated by AMF inoculation at harvest with increased shoot and root biomass. The results suggest that the ameliorative effects of AMF on root damage stress may be related to the regulation of hormone levels and an increase in the percentage of fine roots which was conducive to the growth of roots and leaves and increased plant resistance to environmental stress. In addition, analysis of variable distributions shows that the ameliorative effects of AMF were affected by the degree of root damage. [ABSTRACT FROM AUTHOR]

Experiments were conducted to assess the role of colonization of alfalfa roots by an arbuscular mycorrhizal (AM) fungus (Glomus etunicatum) in conjunction with a non-ionic surfactant (Triton X-100) in dissipation of phenanthrene in a soil spiked with phenanthrene at 0, 2.5, 5.0 and 10.0 mg kg−1. After plant harvest the residual phenanthrene concentration in the soil decreased markedly. Mycorrhizal treatment enhanced phenanthrene dissipation in the rhizosphere and bulk soils irrespective of phenanthrene application rate. Addition of Triton X-100 resulted in the highest phenanthrene concentration in the rhizosphere soil among the treatments, while the lowest phenanthrene concentration in the bulk soil was obtained by AM inoculation and amendment with Triton X-100. AM inoculation and addition of the surfactant consistently promoted phenanthrene dissipation in the soil and decreased the microbial biomass based on phospholipid fatty acid (PLFA) analysis. PLFA profiles demonstrated that AM inoculation together with addition of Triton X-100 altered the microbial community structure in the rhizosphere soil. The results of this study provide a reference value for phytoremediation of soil contaminated by organic pollutants. [Copyright &y& Elsevier]

• Revegetation types affected AMF communities and SOC fractions in mining reclamation. • Nitrogen-fixing plants could release soil nutrients to improve AMF community. • Soil pH, SOC and C:N ratio play a key role in shifting the AMF community. • AMF, revegetation types and SOC fractions had coupling biological relationship. The rhizosphere arbuscular mycorrhizal fungal (AMF) community and soil organic carbon (SOC) fractions are important in vegetation restoration because they can promote plant growth and environmental improvement in the mining subsidence area of northwest China. However, the effects of revegetation type on SOC fractions and the AMF community remain poorly understood despite their importance in promoting sustainable environmental development. Here, we have examined the rhizosphere soil AMF community and SOC fractions of five revegetation types comprising Amorpha fruticosa (AF), Hippophae rhamnoides (HR), Xanthoceras sorbifolium (XS), Cerasus humilis (CH), and Cerasus szechuanica (CS). Revegetation type significantly affected AMF α-diversity, communities and SOC fractions. The contents of soil microbial biomass carbon, dissolved organic carbon, readily oxidized organic carbon and readily extractable glomalin were maximum in HR. We found six genera of AMF (Glomus , Scutellospora , Paraglomus , Claroideoglomus , Ambispora and Diversispora) and Glomus was the most frequently occurring genus in each revegetation type. Nitrogen-fixing plants (AF and HR) may release large amounts of soil nutrients to promote the activity of the soil AMF community. Soil pH, SOC and C:N ratio play key roles in shifting the AMF community. Interactions between the soil AMF community and revegetation types are key to optimizing the restoration of degraded systems and accumulating soil organic matter. Our observations may provide fundamental guidelines in the assessment of ecosystem services and sustainable development in vegetation reconstruction in the coal mining subsidence areas. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) fungi are very abundant in many agricultural soils and are important in increasing and maintaining the sustainability of agricultural systems. However, high soil fertility, especially high available soil phosphorus (P) status, often limits AM fungal development in intensively managed agricultural systems and results in the C-costs to the host plant outweighing any benefits from AM colonization. Some promising approaches can minimize negative effects on soil biota while providing the desired agricultural benefits (e.g. reduced soil tillage and organic amendments). However, the influence of these agricultural practices on the benefits of root mutualistic associations remains poorly understood. Here, we collected indigenous AM fungi from a long-term field experiment with different application rates of cow manure and conducted a pot experiment with different soil P levels. Using high throughput sequencing we demonstrate that increasing cow manure application changed the community composition of AM fungi and reduced community diversity in the field. Phosphorus addition in a bioassay experiment produced a mycorrhizal growth response (MGR) and the mycorrhizal P response (MPR) shifted from positive to negative, regardless of the origin of the inoculum. An increase in intraradical and extraradical AM fungal structures enhanced maize shoot biomass and P uptake under low (no P added) and moderate (20 mg P added kg−1 soil) P levels but the opposite occurred at a high P level (250 mg P added kg−1 soil). The MGR was higher in the treatment with higher community diversity at the moderate P level but there was no significant correlation at the other two P levels examined. We conclude that available soil P may regulate the abundance and diversity of AM fungi and their symbiotic function in intensive cropping systems. Our results indicate that managing the soil phosphorus level to favor a rich and diverse AM fungal community can enhance crop production and result in a more sustainable agricultural system. • Indigenous AM fungi showed great potential for promoting plant growth and P uptake.. • Increased fertility in the field soil changed the community composition of AM fungi and reduced community diversity. • A higher indigenous AM fungal diversity was more beneficial to plants at a moderate soil P level. [ABSTRACT FROM AUTHOR]

The mechanistic understanding of the dynamic processes linking nutrient acquisition and biomass production of competing individuals can be instructive in optimizing intercropping systems. Here, we examine the effect of inoculation with Funneliformis mosseae on competitive dynamics between wheat and faba bean. Wheat is less responsive to mycorrhizal inoculation. Both inoculated and uninoculated wheat attained the maximum instantaneous N and P capture approximately five days before it attained the maximum instantaneous biomass production, indicating that wheat detected the competitor and responded physiologically to resource limitation prior to the biomass response. By contrast, the instantaneous N and P capture by uninoculated faba bean remained low throughout the growth period, and plant growth was not significantly affected by competing wheat. However, inoculation substantially enhanced biomass production and N and P acquisition of faba bean. The exudation of citrate and malate acids and acid phosphatase activity were greater in mycorrhizal than in uninoculated faba bean, and rhizosphere pH tended to decrease. We conclude that under N and P limiting conditions, temporal separation of N and P acquisition by competing plant species and enhancement of complementary resource use in the presence of AMF might be attributable to the competitive co-existence of faba bean and wheat. [ABSTRACT FROM AUTHOR]