Soil Arbuscular Mycorrhizal Fungi Research Articles

Arbuscular mycorrhizal fungal community structure following different grazing intensities in an alpine grassland

AbstractGrazing alters the plant communities, soil properties, and habitat conditions of the alpine grassland. Arbuscular mycorrhizal fungi (AMF) are involved in the nutrient cycling of grassland ecosystems and form a mutual symbiosis with their host plants. Thus, AMF are sensitive to the impact of livestock grazing. However, the effects of grazing intensity on the AMF community composition and the association between AMF and environmental factors, such as soil physicochemical properties, enzyme activity, and glomalin‐related soil proteins, remain unclear. Here, the response of the soil AMF community to grazing intensity gradients (i.e., light, moderate, and heavy grazing) was studied in an alpine grassland on the Qinghai‐Tibet Plateau. The dominant AMF families included Glomeraceae, Gigasporaceae, Claroideoglomeraceae, Diversisporaceae, and Ambisporaceae. Significant shifts in the AMF community composition in response to grazing intensity were found in both surface and subsurface soils. Soil C/N ratio, plant diversity, soil compactness, chitinase activity, aboveground biomass, total N, soil moisture, and NO3−–N significantly correlated with changes in the AMF community composition. Heavy grazing intensity was associated with the highest AMF alpha diversity, whereas moderate grazing intensity had the lowest AMF alpha diversity in both surface and subsurface soils. Grazing intensity, dominant plants, soil C and N concentrations, and soil compactness were significantly correlated with AMF diversity. These results demonstrated a significant response of the AMF community to grazing intensity, suggesting that plants increase their reliance on AMF symbioses with higher alpha diversity in the heavily degraded alpine grasslands of the Qinghai‐Tibet Plateau.

Profiles and interrelationships of functional soil microbiomes involved in phosphorus cycling in diversified agricultural land‐use systems

AbstractSoil microbiomes play important roles in both transformation and utilization of phosphorus (P) in agroecosystems. By targeting at 18S rRNA, pqqC, and phoD genes, respectively, the community compositions of soil arbuscular mycorrhizal (AM) fungi and inorganic P‐solubilizing and organic P‐mineralizing prokaryotes were investigated across fields with annual crops or vegetables and orchards with peach trees or tea bushes in a common Agri‐technology Park, representing four typical agricultural land‐use types in Eastern China. Both annual crop and vegetable fields exhibited higher soil fertility and phosphatase activity, while both peach tree and tea bush orchards contained greater abundances of AM fungal and pqqC genes. Land‐use type also significantly affected the community compositions of soil AM fungi, and pqqC‐ and phoD‐harboring prokaryotes, with soil available P as the common driver for all functional groups above. Three main ecological clusters (modules) with distinctive interactive features, that is, synergistic, competitive, and inactive were observed in the co‐occurrence network comprised of the three groups involved in P‐cycling. The modules exhibited various distributions among the four land‐use types, and the correlations with soil pH, available P and K, and N:P were shown. Altogether, the results demonstrated the changes in gene abundances, diversity indices, community compositions, and interrelationships of functional groups involved in P‐cycling in response to distinct land‐use types, and highlighting the synergistic potential among groups to alleviate P deficiency.

Spatial changes of arbuscular mycorrhizal fungi in peach and their correlation with soil properties.

Arbuscular mycorrhizal (AM) fungi have beneficial effects on host plants, but their growth is influenced by various factors. This study was carried out to analyze the variation of AM fungi in soils and roots of peach (Prunus persica L. var. Golden Honey 3, a yellow-flesh variety) trees in different soil layers (0–40 cm) and their correlation with soil properties. The peach tree could be colonized by indigenous AM fungi (2.2–8.7 spores/g soil and 1.63–3.57 cm hyphal length/g soil), achieving 79.50–93.55% of root AM fungal colonization degree. The mycorrhizal growth, root sugars, soil three glomalins, NH4+-N, NO3−-N, available P and K, and soil organic matter (SOM) had spatial heterogeneity. Soil spores, but not soil hyphae contributed to soil glomalin, and soil glomalin also contributed to SOM. There was a significant correlation of soil hyphae with spore density, soil NO3−-N, and SOM. Root mycorrhiza was positively correlated with spore density, NH4+-N, NO3−-N, and easily extractable glomalin-related soil protein. Notably, spore density positively correlated with NO3−-N, available K, SOM, and root fructose and glucose, while negatively correlated with available P and root sucrose. These findings concluded that mycorrhiza of peach showed spatial distribution, and soil properties mainly affected/altered based on the soil spore density.

AMF colonization and community of a temperate invader and co-occurring natives grown under different CO2 concentrations for 3 years

AbstractGlobal changes such as atmospheric CO2 enrichment often facilitate exotic plant invasions and alter soil arbuscular mycorrhizal fungi (AMF) community. However, it is still unclear whether the effects of CO2 enrichment on exotic plant invasions are associated with its effects on root-AMF symbiosis of invasive and native plants. To address this issue, the annual invasive plant Xanthium strumarium and two phylogenetically related annual natives were compared under ambient and elevated CO2 concentrations for three consecutive years. Atmospheric CO2 enrichment increased AMF colonization rates for the species only in few cases, and the invader did not benefit more from CO2 enrichment in terms of AMF colonization. Under ambient CO2 concentration, however, the invader had a higher AMF colonization rate than the natives in the first year of the study, which disappeared in the second and third year of the study due to the increase of AMF colonization rates in the natives but not in the invader. The influences of species, CO2 concentrations and planting year on AMF colonization were associated with their effects on both soil nutrient and AMF community, and the former may be more important as it also influenced the latter. Our results indicate that the invader could more quickly form symbiosis with soil AMF, contributing to adaptation and occupation of new habitats, and that it is necessary to consider the roles of AMF and the effects of time when determining the effects of global changes such as atmospheric CO2 enrichment on exotic plant invasions.

Clary Sage Cultivation and Mycorrhizal Inoculation Influence the Rhizosphere Fungal Community of an Aged Trace-Element Polluted Soil.

Soil fungal communities play a central role in natural systems and agroecosystems. As such, they have attracted significant research interest. However, the fungal microbiota of aromatic plants, such as clary sage (Salvia sclarea L.), remain unexplored. This is especially the case in trace element (TE)-polluted conditions and within the framework of phytomanagement approaches. The presence of high concentrations of TEs in soils can negatively affect not only microbial diversity and community composition but also plant establishment and growth. Hence, the objective of this study is to investigate the soil fungal and arbuscular mycorrhizal fungi (AMF) community composition and their changes over time in TE-polluted soils in the vicinity of a former lead smelter and under the cultivation of clary sage. We used Illumina MiSeq amplicon sequencing to evaluate the effects of in situ clary sage cultivation over two successive years, combined or not with exogenous AMF inoculation, on the rhizospheric soil and root fungal communities. We obtained 1239 and 569 fungal amplicon sequence variants (ASV), respectively, in the rhizospheric soil and roots of S. sclarea under TE-polluted conditions. Remarkably, 69 AMF species were detected at our experimental site, belonging to 12 AMF genera. Furthermore, the inoculation treatment significantly shaped the fungal communities in soil and increased the number of AMF ASVs in clary sage roots. In addition, clary sage cultivation over successive years could be one of the explanatory parameters for the inter-annual variation in both fungal and AMF communities in the soil and root biotopes. Our data provide new insights on fungal and AMF communities in the rhizospheric soil and roots of an aromatic plant, clary sage, grown in TE-polluted agricultural soil.

Nitrogen Addition and Arbuscular Mycorrhizal Fungi Beta Diversity: Patterns and Mechanisms

Global nitrogen eutrophication, which is disrupting the intimate plant–arbuscular mycorrhizal fungi (AMF) symbiosis, can alter the diversity and physiological functions of soil AMF greatly. However, shifts of beta diversity and the intrinsic patterns of AMF community dissimilarities in response to nitrogen addition remain unclear. Based on a 7-year nitrogen addition experiment in a Qinghai–Tibet Plateau alpine meadow, we detected the changes in soil AMF alpha diversity (richness and genus abundance) and the community composition beta diversity by partitioning the two components of Simpson and nestedness dissimilarities along (turnover) and within (variation) nitrogen addition treatments, and fitted with environmental factor dissimilarities. We found that nitrogen addition decreased AMF richness by decreasing the most dominant AMF genus of Glomus but increasing the abundance of the rare genera. The turnover of the AMF community overall beta diversity along the nitrogen addition gradients was induced by the increased nestedness dissimilarity, while the variation within treatments was explained by both increased Simpson and nestedness dissimilarities, which was significantly correlated with soil pH. Our study found both Simpson and nestedness dissimilarities worked on the AMF community dissimilarity after nitrogen addition and the significant variation within the same treatment, which would be important in the future for predicting global AMF or microbial diversity changes in response to nitrogen eutrophication.

Soil physicochemical property and arbuscular mycorrhizal fungi resilience to degradation and deforestation of a dry evergreen Afromontane forest in central Ethiopia

AbstractWe investigated the soil physicochemical property and arbuscular mycorrhizal fungi (AMF) resilience to the degradation and deforestation of a dry evergreen Afromontane forest, the Chilimo Forest (CF). Topsoil (1‐10 cm) physicochemical property, AMF spore abundance (SA), and AMF infectivity were determined across four land uses, viz., natural forest (NF), shrubland (ShL), cropland (CrL), and grazing land (GrL). According to the permutational multivariate analysis of variance and nonmetric multidimensional scaling results, soil physicochemical property was resilient to degradation (NF‐ShL conversion) but not deforestation (NF‐CrL or NF‐GrL conversions) of CF. The one‐way ANOVA results indicated that most soil physicochemical variables were significantly (p < 0.05) affected by land‐use change. Soil organic matter and total nitrogen, in particular, reduced significantly (p < 0.05) by up to 48% and 57% due to NF‐CrL and NF‐GrL conversions, respectively. Whereas SA was found to be resilient to both CF degradation and deforestation, AMF infectivity was resilient only to NF‐CrL conversion. Generally, our results did not show a similar pattern in soil physicochemical property, SA, and AMF infectivity resilience to degradation and deforestation. However, in the case of NF‐GrL conversion, both soil physicochemical property and AMF infectivity exhibited significantly (p < 0.05) low resilience. Based on our results, we conclude that soil physicochemical property and AMF are important factors to consider in CF restoration planning. When planting sites are either the croplands or grazing lands, soil amendment could be recommended. AMF inoculation, however, could be recommended when the planting sites are grazing lands. These recommendations may also apply widely to dry evergreen Afromontane forests restoration but additional studies are required.

Variations in glomalin-related soil protein in Vicia faba rhizosphere depending upon interactions among mycorrhization, daytime and/or nighttime elevated CO2 levels

Relationships between glomalin-related soil protein (GRSP) and soil organic carbon, total nitrogen or enzyme activity are unknown under the combined effects of varying daytime/nighttime elevated CO2 (eCO2) levels and arbuscular mycorrhizal fungi (AMF). We demonstrated that daytime, nighttime, and dual daytime/nighttime eCO2 levels could significantly increase AMF mycorrhization, soil organic carbon, total nitrogen, easily extractable, difficultly extractable and total GRSP in AMF soil. Under daytime eCO2, soil total nitrogen was significantly decreased in non-AMF soil, while mycorrhization alleviated soil nitrogen limitation. Nighttime and dual daytime/nighttime eCO2 significantly increased β-glucosidase and protease activities in AMF and non-AMF soils. With greater eCO2 effects in AMF than in non-AMF soils, GRSPs positively related to mycorrhization, soil organic carbon, total nitrogen, and β-glucosidase activity. Under the circumstance of global CO2 rising, besides mycorrhization, the combined effects of varying, non-steady-state daytime and nighttime eCO2, play important roles in soil carbon and nitrogen cycles.

Role of arbuscular mycorrhizal fungi in soil and water conservation: a potentially unexplored domain

Role of arbuscular mycorrhizal fungi in soil and water conservation: a potentially unexplored domain

Arbuscular mycorrhizal fungal communities of topsoil and subsoil of an annual maize-wheat rotation after 15-years of differential mineral and organic fertilization

Arbuscular mycorrhizal fungi (AMF) could improve crop yield by nutrient uptake from soil. However, how AMF of topsoil and subsoil respond to long-term differential application of mineral and organic fertilizers and how they are influenced in presence of different crops and growth stages have never been assessed together. Next generation sequencing was applied to profile soil AMF communities in both topsoil and subsoil from a typical arable soil (Eutric Regosol) in the Sichuan Base, southwest China. Soils were collected at anthesis and harvest of winter wheat and maize after 15-years of differential fertilization of an annual maize-wheat rotation (same inputs of nitrogen, N; but different in carbon, C; phosphorus, P; and potassium, K): (i) no-fertilization control (CT), (ii) 100% mineral NPK fertilizer (NPK), (iii) 60% mineral N and 100% mineral PK plus 40% N as crop residues (NPKCR); and (iv) 60% mineral N and 100% mineral PK plus 40% N as pig (organic) manure (NPKOM). Compared to CT, AMF diversity significantly decreased in topsoil, but increased in subsoil for both wheat and maize under NPK, NPKCR and NPKOM. The AMF community composition differed between NPK and CT in both topsoil and subsoil of maize and wheat. Both distance-based redundancy analysis (db-RDA) and structural equation modeling (SEM) suggested that AMF communities in topsoil and subsoil of maize and wheat responded in differences in soil available P, soil organic carbon, fertilization and climate (temperature and/or rainfall). Fertilization and available N, not AMF community, had significantly positive effects on wheat and maize aboveground dry matter and grain yield. Results from the present study shed light on how AMF communities in topsoil and subsoil respond to different soil fertility management over the long-term. Insights of this study are valuable in managing an important part of biological soil fertility.

Plant invasion alters community structure and decreases diversity of arbuscular mycorrhizal fungal communities

Invasive plants often pose serious threats to the natural biodiversity of invaded ecosystems and in this way are likely to alter ecosystem services. This applies to arbuscular mycorrhizal (AM) fungi, in which the invaders have been reported to modify community structure, which facilitates their further intrusion. Information as to the impact of such invasion on AM fungal communities is insufficient and therefore needed. In particular, little is known about how AM fungal communities shift in response to individual invasive species. To ascertain whether invasion changes the structure of indigenous AM fungal communities, we examined changes in AM fungal community composition and diversity in soil and in roots of native neighboring plants in response to incursion of five invasive plant species from the family Asteraceae: Conyza canadensis, Erigeron annuus, Echinops sphaerocephalus, Solidago canadensis, and Symphyotrichum novi-belgii. We found that invasions of tested invasive plant species altered composition of the AM fungal community and reduced the diversity of AM fungi in soil and in the roots of some native plants. Statistical significance of the invasions' effects depended on composition of AM fungal communities in roots of the native plant species and/or site and was not connected with changes in soil parameters. Our results confirm the notable influence of plant invasion on indigenous AM fungal biodiversity and the need for further study in various environmental conditions.

Phosphorus fertilization rather than nitrogen fertilization, growing season and plant successional stage structures arbuscular mycorrhizal fungal community in a subtropical forest

Soil arbuscular mycorrhizal (AM) fungi were monitored in a 4-year experiment of nitrogen (N) and phosphorus (P) fertilization in three growing seasons (April, August, and November) under two successional stages (young and mature) in a subtropical forest of China. AM fungal extra-radical hyphal density was significantly affected by fertilization, season, and interactions between fertilization and season and between forest stage and season, but not by forest stage. The spore density of AM fungi was significantly affected by forest stage and season, but not by fertilization. Totally, 160 operational taxonomic units (OTUs) of AM fungi have been identified at a 97% sequence similarity level using Illumina MiSeq sequencing of the V4 region of the 18S rDNA. AM fungal Shannon diversity index, but not OTU richness, showed a positive response to P fertilization. The community composition of AM fungi was significantly influenced by P fertilization, but not by N fertilization, season, and forest stage. Phosphorus fertilization exhibited a negative impact on the relative abundance of the dominant Glomeraceae. This finding highlights that P availability has a strong effect on the community of AM fungi in the subtropical forest ecosystem.

Inoculation of arbuscular mycorrhizal fungi as a strategy to improve annatto (Bixa orellana L.) growth

This study aimed to assess the occurrence of arbuscular mycorrhizal fungi (AMF) in annatto (Bixa orellana L.) cultivars and their response to AMF inoculation using biometric parameters. The occurrence surveys were conducted in annatto fields in three municipalities from Pernambuco Forest Zone: Lagoa de Itaenga, Gloria de Goitá, and Vitoria de Santo Antão, and in four cultivars (Red Piave, Green Piave, Red Peruvian Paulista, and Green Peruvian Paulista). In a greenhouse, biometric parameters of annatto seedlings of Red Piave, Red Peruvian Paulista, Embrapa-36, and Embrapa-37 cultivars inoculated with AMF isolated from annatto fields. The Red Piave cultivar exhibited greater root colonization than the Green Peruvian Paulista in the Lagoa de Itaenga and Vitoria de Santo Antão municipalities. The cultivar Red Piave showed a more beneficial association with AMF in plants and soil than cultivar Green Peruvian Paulista did, in both Lagoa de Itaenga and Vitoria de Santo Antão. AMF inoculation was effective in promoting the growth of annatto plants, particularly those inoculants with S. heterogama and C. etunicatum.

Depression of the soil arbuscular mycorrhizal fungal community by the canopy gaps in a Japanese cedar (Cryptomeria japonica) plantation on Lushan Mountain, subtropical China.

Both canopy gaps (CG) and arbuscular mycorrhizal fungi (AMF) play key roles in seedling establishment and increasing species diversity in forests. The response of AMF to canopy gaps is poorly understood. To assess the long-term effects of canopy gaps on soil AMF community, we sampled soil from plots in a 50-year Cryptomeria japonica (L.f.) D. Don. plantation, located in Lushan Mountain, subtropical China. We analyzed the AMF community, identified through 454 pyrosequencing, in soil and edaphic characteristics. Both richness and diversity of AMF in CG decreased significantly compared to the closed canopy (CC). The differences of the AMF community composition between CG and CC was also significant. The sharp response of the AMF community appears to be largely driven by vegetation transformation. Soil nutrient content also influenced some taxa, e.g., the low availability of phosphorus increased the abundance of Acaulospora. These results demonstrated that the formation of canopy gaps can depress AMF richness and alter the AMF community, which supported the plant investment hypothesis and accentuated the vital role of AMF–plant symbioses in forest management.

Variable effects of mycorrhizal fungi on predator-prey dynamics under field conditions.

Interactions between herbivores and their predators are shaped, in part, by plant phenotype. Consequently, ubiquitous symbionts of plants below-ground, such as arbuscular mycorrhizal fungi (AMF), may influence interactions above-ground between predators and their prey by altering plant phenotype. However, the ecological relevance of below-ground organisms on predator-prey interactions under field conditions remains unclear. We assessed how AMF influence herbivore-predator interactions through a field experiment. We planted two milkweed species (Asclepias curassavica and Asclepias incarnata) provided with different amounts of AMF inoculum (zero, medium, and high) in a randomized block design. We added aphids to plants and reduced predator pressure weekly for 5weeks to evaluate effects of AMF on predator recruitment. We then allowed herbivore-predator interactions to re-establish naturally for the remainder of the season to examine whether AMF-mediated variation in predator recruitment influenced the suppression of aphid populations. Arbuscular mycorrhizal fungi availability in soils mediated interactions between predaceous aphid midge flies Aphidoletes aphidimyza and their aphid prey Aphis nerii, but the effects were plant species-specific. On A. curassavica, by mid-season, midges were recruited most strongly on plants under medium AMF availability and least on plants under high AMF availability. In contrast, each midge killed fewer aphids with increasing aphid density on medium AMF plants, but killed more aphids with increasing aphid density on high AMF plants. In combination, aphid mortality rates imposed by midges were greatest on medium AMF plants, followed by high and zero AMF plants. By comparison, on A. incarnata, the recruitment of midges was strongest on high AMF plants and weakest on medium AMF plants. AMF had no effect on the number of aphids killed per midge, relative to aphid density, so mortality rates of aphids imposed by midges mirrored recruitment. Rates of decline in aphid populations following predator recolonization were associated with midge densities, as well as lacewing and syrphid densities, which were unaffected by AMF availability. Therefore, the effects of AMF on aphid population decline were not a simple function of AMF-midge interactions. Our findings demonstrate that the availability of AMF in soils has pervasive, but complex, effects on predator-herbivore dynamics in the field.

Effect of land use type on arbuscular mycorrhizal fungi diversity in high altitude of Karo Highland

This study evaluated the spore density and diversity of arbuscular mycorrhizal fungi (AMF) in different land use type at Karo Highland. Sampling of soil AMF was conducted once as a material for trap culture by using Pueraria javanica as a host. The trap culture was used to observe the spore density and percentage of root colonization. The results showed that spore density and AMF colonization was not affected by different land use type, but rather by soil chemical properties. Soil acidity and phosphorus content had negative effect on root abundance and colonization, while carbon, nitrogen and potassium content gave positive effects. This study found 15 AMF spores from all types of land use dominated by Glomaceae followed by Acaulosporaceae and Gigasporaceae. The occurrence of AMF species was not specific to one type of land use but rather evenly dispersed in all types.

The genome of Geosiphon pyriformis reveals ancestral traits linked to the emergence of the arbuscular mycorrhizal symbiosis

Arbuscular mycorrhizal fungi (AMF) (subphylum Glomeromycotina)1 are among the most prominent symbionts and form the Arbuscular Mycorrhizal symbiosis (AMS) with over 70% of known land plants.2,3 AMS allows plants to efficiently acquire poorly soluble soil nutrients4 and AMF to receive photosynthetically fixed carbohydrates. This plant-fungus symbiosis dates back more than 400 million years5 and is thought to be one of the key innovations that allowed the colonization of lands by plants.6 Genomic and genetic analyses of diverse plant species started to reveal the molecular mechanisms that allowed the evolution of this symbiosis on the host side, but how and when AMS abilities emerged in AMF remain elusive. Comparative phylogenomics could be used to understand the evolution of AMS.7,8 However, the availability of genome data covering basal AMF phylogenetic nodes (Archaeosporales, Paraglomerales) is presently based on fragmentary protein coding datasets.9Geosiphon pyriformis (Archaeosporales) is the only fungus known to produce endosymbiosis with nitrogen-fixing cyanobacteria (Nostoc punctiforme) presumably representing the ancestral AMF state.10-12 Unlike other AMF, it forms long fungal cells ("bladders") that enclose cyanobacteria. Once in the bladder, the cyanobacteria are photosynthetically active and fix nitrogen, receiving inorganic nutrients and water from the fungus. Arguably, G.pyriformis represents an ideal candidate to investigate the origin of AMS and the emergence of a unique endosymbiosis. Here, we aimed to advance knowledge in these questions by sequencing the genome of G.pyriformis, using a re-discovered isolate.

Arbuscular Mycorrhizal Fungi Regulate Polyamine Homeostasis in Roots of Trifoliate Orange for Improved Adaptation to Soil Moisture Deficit Stress.

Soil arbuscular mycorrhizal fungi (AMF) enhance the tolerance of plants against soil moisture deficit stress (SMDS), but the underlying mechanisms are still not fully understood. Polyamines (PAs) as low-molecular-weight, aliphatic polycations have strong roles in abiotic stress tolerance of plants. We aimed to investigate the effect of AMF (Funneliformis mosseae) inoculation on PAs, PA precursors, activities of PA synthases and degrading enzymes, and concentration of reactive oxygen species in the roots of trifoliate orange (Poncirus trifoliata) subjected to 15 days of SMDS. Leaf water potential and total chlorophyll levels were comparatively higher in AMF-inoculated than in non-AMF-treated plants exposed to SMDS. Mycorrhizal plants recorded a significantly higher concentration of precursors of PA synthesis such as L-ornithine, agmatine, and S-adenosyl methionine, besides higher putrescine and cadaverine and lower spermidine during the 15 days of SMDS. AMF colonization raised the PA synthase (arginine decarboxylase, ornithine decarboxylase, spermidine synthase, and spermine synthase) activities and PA-degrading enzymes (copper-containing diamine oxidase and FAD-containing polyamine oxidase) in response to SMDS. However, mycorrhizal plants showed a relatively lower degree of membrane lipid peroxidation, superoxide anion free radical, and hydrogen peroxide than non-mycorrhizal plants, whereas the difference between them increased linearly up to 15 days of SMDS. Our study concluded that AMF regulated PA homeostasis in roots of trifoliate orange to tolerate SMDS.

Effects of elevated CO2 on arbuscular mycorrhizal fungi associated with Robinia pseudoacacia L. grown in cadmium-contaminated soils

As symbionts capable of reciprocal rewards, arbuscular mycorrhizal fungi (AMF) can alleviate heavy metal toxicity to host plants and are easily influenced by elevated CO2 (ECO2). Although the individual effects of ECO2 and cadmium (Cd) on AMF have been widely reported, the response of AMF to ECO2 + Cd receives little attention. We evaluated the combined effects of ECO2 and Cd on AMF in the rhizosphere soil and roots of Robinia pseudoacacia L. seedlings. Under ECO2 + Cd relative to Cd, AMF gene copies and richness in rhizosphere soils increased (p < 0.05) and the diversity reduced (p < 0.05) at 4.5 mg Cd kg−1 dry soil; whereas root AMF abundance at 4.5 mg Cd kg−1 dry soil and the diversity and richness reduced (p < 0.05). Elevated CO2 caused obvious differences in the dominant genera abundance between rhizosphere soils and roots upon Cd exposure. Responses of C, water-soluble organic nitrogen (WSON), pH, and diethylene triamine penta-acetic acid (DTPA)-Cd in rhizosphere soils and root N to ECO2 shaped dominant genera in Cd-polluted rhizosphere soils. Levels of DTPA-Cd, WSON, C and pH in rhizosphere soils and C/N ratio, N, and Cd in roots to ECO2 affected (p < 0.05) dominant genera in roots under Cd exposure. AMF richness and diversity were lower in roots than in rhizosphere soils. Elevated CO2 altered AMF communities in rhizosphere soils and roots of R. pseudoacacia seedlings exposed to Cd. AMF associated with R. pseudoacacia may be useful/interesting to be used for improving the phytoremediation of Cd under ECO2.

生物炭对褐土旱地玉米季氮转化功能基因、丛枝菌根真菌及N2O释放的影响

以豫西旱地玉米农田为研究对象，设置不同生物炭施用量处理（T0：不施用生物炭；T1：施用生物炭20 t/hm²；T2：施用生物炭40 t/hm²），采用密闭式静态箱法测定N₂O排放通量和荧光定量PCR法分析丛枝菌根（arbuscular mycorrhizal，AM）真菌、氨单加氧酶（amoA）、亚硝酸盐还原酶（nirS、nirK）以及氧化亚氮还原酶（nosZ）的基因丰度，同时测定土壤理化性状的变化。研究结果表明，随着生物炭施用量的增加，土壤pH和含水量呈增加趋势，土壤有机碳、全氮和铵态氮含量显著提高，土壤容重和硝态氮含量显著降低。T1和T2处理土壤有机碳含量分别较T0显著提高38.44%和71.01%；T1和T2处理土壤铵态氮含量分别较T0显著增加15.89%和30.46%；T2处理土壤全氮含量较T0处理显著提高14.87%；T1和T2处理土壤硝态氮含量分别较T0减少10.57%和21.40%。随着生物炭施用量的增加，AM真菌侵染率显著增加，T1和T2处理分别较T0处理提高71.88%和115.88%；AOA、AOB、nirK和nirS基因丰度显著降低；nosZ基因丰度增加。施加生物炭处理的N₂O排放通量和累积排放量均低于不施生物炭处理，具体表现为：T0 > T1 > T2。相关分析表明，生物炭施用量与AM真菌基因丰度呈显著正相关；与nosZ基因丰度呈正相关；与AOA、AOB、nirK、nirS基因丰度呈极显著负相关。N₂O排放通量与AOA、nirK、nirS基因丰度呈极显著正相关；与土壤含水量和土壤硝态氮含量呈显著正相关；与AM真菌、nosZ基因丰度、易提取球囊霉素含量、铵态氮含量呈极显著负相关。集成推进树（ABT）分析表明，AOA对N₂O排放的影响最大，其次是AM真菌和nirS。总之，生物炭处理改善土壤理化性质、提高土壤AM真菌侵染率、调节硝化、反硝化相关功能基因的丰度，减少N₂O气体排放，为旱地农田合理施用生物炭减少N₂O气体排放提供理论依据。;Biochar soil amendments are attracting the increased attention as one strategy to improve soil microbially ecological environment and regulate soil nitrogen cycle. The rainfed maize cropland in the western Henan was established to study the effects of biochar application rates (T0:0 t/hm², T1:20 t/hm², and T2:40 t/hm²) on soil physicochemical properties and N₂O emission fluxes using the static chamber/gas chromatography method, and the function marker genes of arbuscular mycorrhizal (AM) fungi, ammonia monooxygenase gene (amoA), nirK, nirS and nosZ, which were responsible for nitrification and denitrification using real-time fluorescence quota PCR. The results showed that the soil pH and water content increased, soil organic carbon, total nitrogen and ammonium nitrogen content increased significantly, and soil bulk density and nitrate nitrogen content decreased significantly with increasing biochar applied. Compared with T0 treatment, soil organic carbon increased significantly by 38.44% and 71.01% under T1 and T2 treatments, respectively; soil ammonium nitrogen content increased significantly by 15.89% and 30.46% under T1 and T2 treatments, respectively; soil total nitrogen content increased significantly by 14.87% under T2 treatment; nitrate nitrogen content decreased by 10.57% and 21.40% under T1 and T2 treatments, respectively. Moreover, the AM fungi colonization rate and nosZ gene abundance increased significantly, and AOA, AOB, nirK and nirS gene abundance decreased significantly with increasing biochar applied. Compared with T0 treatment, AM fungi increased significantly by 71.88% and 115.88% under T1 and T2 treatments, respectively. The N₂O emission fluxes and emission accumulations under biochar addition were all lower than those under no biochar, ranked as T0 > T1 > T2. The correlation analysis showed that the abundance of AM fungi was significantly positively (P<0.05) correlated with the biochar rate, and the abundance of nosZ gene and biochar rate was significant. There was a significantly negative correlation between AOA, AOB, nirK, nirS gene abundance and biochar rate (P<0.01). The N₂O emission fluxes showed a significantly positive correlation (P<0.01) with AOA, nirK, nirS, soil water content and nitrate nitrogen, but significantly negatively (P<0.01) correlated with AM fungi, nosZ, ammonium nitrogen and extractable glomalin related soil protein content. Aggregated boosted trees (ABT) analysis showed that the relative influence of AOA on N₂O emission fluxes was the largest, followed by AM fungi and nirK. In summary, the application of biochar improved soil physicochemical properties, increased soil AM fungi colonization rates, regulated nitrification and denitrification functional genes, and reduced N₂O emission, which provided a theoretical basis for the rational application of biochar and reduction of N₂O emissions in rainfed maize cropland.