Arbuscular Mycorrhizal Fungi Colonization Rate Research Articles

Arbuscular mycorrhizal colonization rate of an exotic plant, Galinsoga quadriradiata, in mountain ranges changes with altitude.

Arbuscular mycorrhizal fungi (AMF) are suggested to be important for invasions by many exotic plants. However, it is not yet known how associations between AMF and invasive plant populations change in mountains ranges and how changed associations affect further expansion of different populations in new habitats. We conducted a field survey to detect AMF colonization rate of the invasive Galinsoga quadriradiata along an elevational gradient ranging from 223 to 1947masl in the Qinling and Bashan Mountains, China. Additionally, a greenhouse experiment was conducted to compare plant growth performance among five elevational populations. In the field, total plant mass and seed production, as well as root AMF colonization rate, significantly decreased with elevation. When populations were grown in a novel soil environment in the greenhouse, the high-altitude populations achieved higher seed and total mass at lower AMF colonization rate than the low-altitude populations. Moreover, high AMF association was related to high intraspecific competition within low-altitude populations and limited seed production. Our results revealed that the associations between AMF and G. quadriradiata decrease with altitude in mountain ranges, and this may indicate that differentiation of association between AMF and elevational populations occurs during range expansion of G. quadriradiata. The results of the greenhouse experiment suggest that the high-altitude populations are more aggressive than the low-altitude populations in a non-stressful environment.

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.

Effects of nitrogen deposition and phosphorus addition on arbuscular mycorrhizal fungi of Chinese fir (Cunninghamia lanceolata)

Nitrogen (N) deposition is a key factor that affects terrestrial biogeochemical cycles with a growing trend, especially in the southeast region of China, where shortage of available phosphorus (P) is particularly acute and P has become a major factor limiting plant growth and productivity. Arbuscular mycorrhizal fungi (AMF) establish a mutualistic symbiosis with plants, and play an important role in enhancing plant stress resistance. However, the response of AMF to the combined effects of N deposition and P additions is poorly understood. Thus, in this study, a field experiment was conducted in 10-year Chinese fir forests to estimate the effects of simulated nitrogen (N) deposition (low-N, 30 kg ha−1 year−1 and high-N, 60 kg ha−1 year−1) and phosphorus (P) addition treatments (low-P, 20 mg kg−1 and high-P, 40 mg kg−1) on AMF since April 2017, which was reflected in AMF root colonization rates and spore density of rhizosphere soil. Our results showed that N deposition significantly decreased AMF root colonization rates and spore density. In N-free plots, P addition significantly decreased AMF root colonization rates, but did not significantly alter spore density. In low-N plots, colonization rates significantly decreased under low P addition, but significantly increased under high P addition, and spore density exhibited a significant decline under high P additions. In high-N plots, colonization rates and spore density significantly increased under P additions. Interactive effects of simulated N deposition and P addition on both colonization rates and spore density were significant. Moderate N deposition or P addition can weaken the symbiotic relationship between plants and AMF, significantly reducing AMF colonization rates and inhibiting spore production. However, a moderate addition of P greatly enhances spore yield. In the case of interactive effects, the AMF colonization rates and spore density are affected by the relative content of N and P in the soil.

Salinity changes root occupancy by arbuscular mycorrhizal fungal species

Understanding the diversity and community composition of arbuscular mycorrhizal (AM) fungi in stressful conditions is fundamental to predicting the occurrence and function of indigenous AM fungal associations in a changing soil environment. Here, using whole-soil inoculum, we investigated the effects of salinity on community structure and colonization rate of AM fungi in roots, and assessed their influence on maize (Zea mays L.) performance. Three different salinity treatments (0, 75, and 150 mM NaCl) were applied to mycorrhizal inoculated and non-inoculated plants. Results showed that salinity levels significantly influenced AM fungal composition and diversity as well as vesicular and hyphal colonization in roots. The AM fungal community composition and diversity index differed slightly under the 0 and 75 mM NaCl treatments, but changed significantly under the 150 mM NaCl treatment. Increased vesicular and declined hyphal colonization were observed under 75 and 150 mM NaCl treatments relative to the control. Further analyses uncovered that plants under the 0 and 75 mM NaCl treatments, where Glomeraceae predominated as root symbionts, had a higher mycorrhizal growth response than plants under the 150 mM NaCl treatment, where Claroideoglomeraceae abundance increased significantly. This study provides evidence that saline stress plays a vital role in community structure and root colonization by AM fungal communities. Additionally, our data suggested that community composition may be more important for mycorrhizal symbiotic function than the rate of root colonization. Finally, while the relative abundance of Claroideoglomeraceae was found to increase with stress in saline soil, their role needs to be further clarified in future studies.

Arbuscular mycorrhizal fungus identity modulates growth effects of endophyte-infected grasses on neighboring plants.

Endophytes of grasses have been reported to affect the colonization by arbuscular mycorrhizal fungi (AMF) not only of their dual host plant but also of neighboring non-endophyte-infected plants. However, studies investigating the impact of AMF identity on the effects of endophyte-infected grasses on neighboring plants are rare. In this study, we investigated the influence of Leymus chinensis litter type (NL, no litter; E-, endophyte-free litter; E-E+, half E+ and half E- litter; E+, endophyte-infected litter) on Stipa krylovii growth with different AMF species (Claroideoglomus etunicatum, CE; Funneliformis mosseae, FM; Claroideoglomus claroideum, CC; Rhizophagus intraradices, RI). The results showed that the root biomass of S. krylovii tended to decrease with the increase of E+ litter in the mycorrhiza-free treatment. With AMF inoculation, the effects of E+ litter on the AMF colonization rate and root biomass of S. krylovii varied with AMF species. Structural equation modeling (SEM) showed E+ litter could modulate the growth of S. krylovii indirectly via changes in AMF colonization rate, but this effect was related to AMF species.

The Interaction of Arbuscular Mycorrhizal Fungi and Phosphorus Inputs on Selenium Uptake by Alfalfa (Medicago sativa L.) and Selenium Fraction Transformation in Soil.

Selenium (Se) is a beneficial element to plants and an essential element to humans. Colonization by arbuscular mycorrhizal fungi (AMF) and supply of phosphorus (P) fertilizer may affect the bioavailability of Se in soils and the absorption of Se by plants. To investigate the interaction between AMF and P fertilizer on the transformation of soil Se fractions and the availability of Se in the rhizosphere of alfalfa, we conducted a pot experiment to grow alfalfa in a loessial soil with three P levels (0, 5, and 20 mg kg-1) and two mycorrhizal inoculation treatments (without mycorrhizal inoculation [−AMF] and with mycorrhizal inoculation [+AMF]), and the interaction between the two factors was estimated with two-way ANOVA. The soil in all pots was supplied with Se (Na2SeO3) at 1 mg kg-1. In our results, shoot Se concentration decreased, but plant Se content increased significantly as P level increased and had a significant positive correlation with AMF colonization rate. The amount of total carboxylates in the rhizosphere was strongly affected by AMF. The amounts of rhizosphere carboxylates and alkaline phosphatase activity in the +AMF and 0P treatments were significantly higher than those in other treatments. The concentration of exchangeable-Se in rhizosphere soil had a positive correlation with carboxylates. We speculated that rhizosphere carboxylates promoted the transformation of stable Se (iron oxide-bound Se) into available Se forms, i.e. exchangeable Se and soluble Se. Colonization by AMF and low P availability stimulated alfalfa roots to release more carboxylates and alkaline phosphatase. AMF and P fertilizer affected the transformation of soil Se fractions in the rhizosphere of alfalfa.

Soil Biological Properties and Arbuscular Mycorrhizal Fungal Communities of Representative Crops Established in the Andean Region from Ecuadorian Highlands

Biological activities determine quality, sustainability, health, and fertility of soils. The purpose of this study was to evaluate chemical and biological characteristics of soils from Ecuadorian highlands subjected to different management practices, as well as the density and diversity of arbuscular mycorrhizal fungi (AMF). Soils from naturalized grasslands and other previously cropped plots with Zea mays and Solanum tuberosum were analyzed in laboratory for soil biochemical properties, enzyme activity, and AMF colonization to determine the effect of the soil management over its quality. The characterization of AMF propagules associated to spontaneously colonizing plants in the above soils was also performed. Soil previously cropped with S. tuberosum showed the highest glomalin content; at the same time, naturalized grassland and Z. mays cropped soils showed higher hyphal length. The acid phosphatase activity was higher in naturalized grasslands and Z. mays cropped soils compared with that in the S. tuberosum cropped soils. Moreover, the highest AMF colonization rates and spore number were found in different spontaneous plant species growing in the naturalized grasslands. This study represents the first characterization of AMF propagules of different cropped and naturalized grassland soils, and also is one of the first reports about changes on biochemical and microbial activities occurring in Andean soils from the highlands of Ecuador, undergoing determinant soil management activities.

VBA-AMF: A VBA Program Based on the Magnified Intersections Method for Quantitative Recording of Root Colonization by Arbuscular Mycorrhizal Fungi.

The extent of mycorrhizal fungi colonization is an important factor for determining the function of mycorrhizal fungi in fungi-host interaction, and quantifying the extent of mycorrhizal fungi colonization is a fundamental and essential task for researchers engaged in mycorrhizal studies. Intersect methods, such as the gridline intersect and magnified intersections methods, are accurate and objective, and are widely used to assess the colonization status of arbuscular mycorrhizal (AM) fungus. However, no convenient procedures or add-ins for Excel spreadsheets have been developed to simplify these methods. Here, we propose a procedure using the Visual Basic for Application (VBA) program in Excel that is based on the magnified intersections method, which we refer to as VBA-AMF (arbuscular mycorrhizal fungi). Time-saving and convenience are the two most prominent advantages of the VBA-AMF procedure, as it enables researchers to compute the colonization rate of AM fungi in roots, and consequently the extent of root colonization by AM fungi. VBA-AMF can also be modified to measure the status of other fungal colonizations in plant roots following the same strategy.

Role of Melatonin in Arbuscular Mycorrhizal Fungi-Induced Resistance to Fusarium Wilt in Cucumber.

Melatonin is a multifunctional molecule that confers tolerance to a number of biotic and abiotic stresses in plants. However, the role of melatonin in plant response to Fusarium oxysporum and the interaction with arbuscular mycorrhizal fungi (AMF) remain unclear. Here we show that exogenous melatonin application promoted the AMF colonization rate in cucumber roots, which potentially suppressed Fusarium wilt as evidenced by a decreased disease index and an increased control effect. Leaf gas exchange analysis revealed that Fusarium inoculation significantly decreased the net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentrations (Ci), and transpiration rate (Tr). Intriguingly, either melatonin application or AMF inoculation significantly increased the Pn, Gs, Tr, and dry biomass, and their combined treatment showed a more profound effect under Fusarium stress. Further analysis showed that Fusarium induced oxidative stress as evidenced by increased lipid peroxidation and electrolyte leakage. Conversely, either melatonin or AMF drastically attenuated the levels of malondialdehyde, H2O2, and electrolyte leakage in Fusarium-inoculated plants, and their combined treatment caused a further decrease. Fusarium inoculation decreased the activity and transcripts of superoxide dismutase and ascorbate peroxidase, and the content of glutathione and proline. Besides, the activity and transcripts of peroxidase and catalase, the content of phenols and flavonoids increased after Fusarium infection. Importantly, melatonin and/or AMF significantly increased those parameters with the greatest effect with their combined treatment under Fusarium stress. Our results suggest that a positive collaboration between melatonin and AMF enhances resistance to Fusarium wilt in cucumber plants.

Global metabolic changes induced by arbuscular mycorrhizal fungi in oregano plants grown under ambient and elevated levels of atmospheric CO2

Symbiotic plant-microorganisms interaction is a promising approach to avoid the environmental hazards of synthetic fertilizers and pesticides. Among these, arbuscular mycorrhizal fungi (AMF) are known to improve the growth and quality of many plant species; however the detailed metabolic mechanisms behind such beneficial effects are far from complete. Further, elevated levels of atmospheric CO2 (eCO2) could affect such AMF-plant association. Herein, we have investigated the individual and synchronous impact of AMF and eCO2 (620 ppm) on nutrient uptake, growth, photosynthesis, respiration, and levels of primary and secondary metabolites in oregano (Oreganum vulgare), an economically important herbal plant. Enhanced AMF colonization rate and a better mycelial growth were observed in roots of oregano grown under eCO2. Both AMF and eCO2 treatments significantly enhanced the growth and photosynthesis of oregano plants, however much improvements were observed by their synchronous application. eCO2 further increased the AMF-induced dark respiration and accumulation of macro and microelements. Hierarchical clustering analysis of individual primary and secondary metabolites revealed a metabolite-dependent response toward AMF and eCO2. The synchronous application of AMF and eCO2 resulted in promoted accumulation of the majority of the detected sugars, organic acids, amino acids, unsaturated fatty acids, phenolic acids and flavonoids, as compared with the sole treatments. Moreover, AMF and eCO2 acted synergistically in improving the antioxidant capacity and anti-lipid peroxidation activity of oregano. Therefore, this study suggests that AMF treatment induces a global metabolic change in oregano, the effect that is strengthened under eCO2.

The Full-Size ABCG Transporter of Medicago truncatula Is Involved in Strigolactone Secretion, Affecting Arbuscular Mycorrhiza.

Strigolactones (SLs) are plant-derived signaling molecules that stimulate the hyphal branching of arbuscular mycorrhizal fungi (AMF), and consequently promote symbiotic interaction between the fungus and the plant. Currently, our knowledge on the molecular mechanism of SL transport is restricted to the Solanaceae family. In the Solanaceae family, SL translocation toward the rhizosphere occurs through the exodermis via hypodermal passage cells and involves a member of the G subfamily, of the ATP-binding cassette (ABC) membrane transporters. Most Fabaceae species, including those that are agriculturally important, have a different root anatomy compared to most angiosperm plants (i.e., lacking an exodermis). Thus, we have investigated how SL transport occurs in the model legume Medicago truncatula. Here, we show that overexpression of a SL transporter from petunia (PaPDR1) enhances AMF colonization rates in M. truncatula. This result demonstrates the importance of ABCG proteins for the translocation of orobanchol-type molecules to facilitate arbuscular mycorrhiza, regardless of root anatomy and phylogenetic relationships. Moreover, our research has led to the identification of Medicago ABCG59, a close homologue of Petunia PDR1, that exhibits root specific expression and is up-regulated by phosphate starvation as well as in the presence of rac-GR24, a synthetic SL. Its promoter is active in cortical cells, root tips, and the meristematic zone of nodules. The mtabcg59 loss-of-function mutant displayed a reduced level of mycorrhization compared to the WT plants but had no impact on the number of nodules after Sinorhizobium meliloti inoculation. The reduced mycorrhization indicates that less SLs are secreted by the mutant plants, which is in line with the observation that mtabcg59 exudates exhibit a reduced stimulatory effect on the germination of the parasitic plant Phelipanche ramosa compared to the corresponding wild type.

Root flavonoids are related to enhanced AMF colonization of an invasive tree.

Arbuscular mycorrhizal fungi (AMF) are important mutualistic microbes in soil, which have capacity to form mutualistic associations with most land plants. Arbuscular mycorrhizal fungi play an important role in plant invasions and their interactions with invasive plants have received increasing attention. However, the chemical mechanisms underlying the interactions of AMF and invasive plants are still poorly understood. In this study we aim to test whether root secondary chemicals are related to enhanced AMF colonization and rapid growth in an invasive tree. We conducted a common garden experiment in China with Chinese tallow tree (Triadica sebifera) to examine the relationships among AMF colonization and secondary metabolites in roots of plants from introduced (USA) and native (China) populations. We found that AMF colonization rate was higher in introduced populations compared to native populations. Roots of plants from introduced populations had lower levels of phenolics and tannins, but higher levels of flavonoids than those of plants from native populations. Flavonoids were positively correlated with AMF colonization, and this relationship was especially strong for introduced populations. Besides, AMF colonization was positively correlated with plant biomass suggesting that higher root flavonoids and AMF colonization may impact plant performance. This suggests that higher root flavonoids in plants from introduced populations may promote AMF spore germination and/or attract hyphae to their roots, which may subsequently increase plant growth. Overall, our results support a scenario in which invasive plants enhance their AMF association and invasion success via genetic changes in their root flavonoid metabolism. These findings advance our understanding of the mechanisms underlying plant invasion success and the evolutionary interactions between plants and AMF. Understanding such mechanisms of invasive plant success is critical for predicting and managing plant invasions in addition to providing important insights into the chemical mechanism of AMF–plant interactions.

Tall Fescue and E. coenophiala Genetics Influence Root-Associated Soil Fungi in a Temperate Grassland.

A constitutive, host-specific symbiosis exists between the aboveground fungal endophyte Epichloë coenophiala (Morgan-Jones & W. Gams) and the cool-season grass tall fescue (Lolium arundinaceum (Schreb.) Darbysh.), which is a common forage grass in the United States, Australia, New Zealand, and temperate European grasslands. New cultivars of tall fescue are continually developed to improve pasture productivity and animal health by manipulating both grass and E. coenophiala genetics, yet how these selected grass-endophyte combinations impact other microbial symbionts such as mycorrhizal and dark septate fungi remains unclear. Without better characterizing how genetically distinct grass-endophyte combinations interact with belowground microorganisms, we cannot determine how adoption of new E. coenophiala-symbiotic cultivars in pasture systems will influence long-term soil characteristics and ecosystem function. Here, we examined how E. coenophiala presence and host × endophyte genetic combinations control root colonization by belowground symbiotic fungi and associated plant nutrient concentrations and soil properties in a 2-year manipulative field experiment. We used four vegetative clone pairs of tall fescue that consisted of one endophyte-free (E−) and one E. coenophiala-symbiotic (E+) clone each, where E+ clones within each pair contained one of four endophyte genotypes: CTE14, CTE45, NTE16, or NTE19. After 2 years of growth in field plots, we measured root colonization of arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE), extraradical AMF hyphae in soil, total C, N, and P in root and shoot samples, as well as C and N in associated soils. Although we observed no effects of E. coenophiala presence or symbiotic genotype on total AMF or DSE colonization rates in roots, different grass-endophyte combinations altered AMF arbuscule presence and extraradical hyphal length in soil. The CTE45 genotype hosted the fewest AMF arbuscules regardless of endophyte presence, and E+ clones within NTE19 supported significantly greater soil extraradical hyphae compared to E− clones. Because AMF are often associated with improved soil physical characteristics and C sequestration, our results suggest that development and use of unique grass-endophyte combinations may cause divergent effects on long-term ecosystem properties.

Nurse effects mediated by acid-tolerance of target species and arbuscular mycorrhizal colonization in an acid soil

We tested whether a nurse-plant effect depends on target-seedling tolerance to soil acidity and arbuscular mycorrhizal fungi (AMF) in an acid soil. A mesocosm experiment was used to assess the acid-tolerance of the seedlings of four target species. Field experiment 1 tested the nurse effects of an adult plant (Lespedeza formosa) on germination rate, seedling survival rate, growth and AMF colonization rate of target seedlings growing in an acid soil. Field experiment 2 tested the influence of AMF root colonization on nurse-plant effects. Target species greatly varied in their tolerance to soil acidity while nurse-effect on target species were mediated by target species acid-tolerance and AMF root colonization. In field experiment 1, as expected, nurse-effect was positive for acid-sensitive species and negative for acid-tolerant species. While nurse plant presence facilitated the germination, survival, growth, and AMF colonization of the two acid-sensitive species it competed with the two acid-tolerant species. In field experiment 2, the nurse plant facilitated the growth of the acid-sensitive seedlings more under AMF not suppressed treatment than AMF suppressed treatment. For the acid-tolerant seedlings, however, the nurse plant reduced their growth under AMF not suppressed treatment, but did not affect their growth under AMF suppressed treatment. Nurse plant facilitated the acid-sensitive species in an acid soil, and the facilitation was enhanced by increasing AMF in the soil. These findings highlight how acid-tolerance of target species and AMF colonization mediates nurse plant facilitation and has important implications for the use of nurse plants in the restoration of acid soils ecosystems.

Arbuscular Mycorrhizal Fungi Associated with Tree Species in a Planted Forest of Eastern China

Arbuscular mycorrhizal fungi (AMF) play an important role in the establishment and maintenance of plant communities in forest ecosystems. Most previous studies about AMF have been conducted in natural forests, and little attention has been paid to trees in planted forests. This study investigated AMF associated with tree species and the relationships between edaphic factors and AMF communities in a planted forest of eastern China. We found high total AMF colonization rates in the roots of Carya illinoensis (Wangenh.) K. Koch, Zelkova serrata (Thunb.) Makinoz, Taxodium ‘zhongshansha’, Eucommia ulmoides Oliv., and Elaeagnus pungens Thunb., ranging from 62.07% to 100%, indicating that AMF can establish effective symbiotic relationships with these tree species. The AMF colonization rate was significantly and negatively correlated with soil phosphorus, while AMF colonization intensity was significantly and negatively correlated with soil moisture content, total carbon, and organic matter content. Spore density was in the range of 4.38 to 76.38 spores per g soil. In total, 35 AMF species from 10 genera were identified. Glomus and Acaulospora were the dominant genera. Acaulospora foveata and Septoglomus constrictum were the dominant species. AMF communities differed among the tree species and were closely related to edaphic factors, and AMF diversity was significantly related to soil carbon and pH. Our results revealed the colonization, community, and diversity of AMF associated with tree species, as well as their relationships with edaphic factors, in planted forests. Our findings can be used to provide insight on the utilization and management of AMF to maintain sustainable management of planted forests.

Endophytic Fungal Root Colonization of Eragrostis tef in Eroded Croplands of the Ethiopian Highlands Is Limited by Low Spore Density and Fertilisation

Eragrostis tef (teff) is a (sub-)tropical cereal crop and a staple food in Eastern Africa. As soil erosion has become increasingly worse in the Ethiopian highlands, we test the hypotheses that (1) eroded soils possess low arbuscular mycorrhizal fungi (AMF) spore densities, (2) teff growth is limited by low endophytic fungal root colonization rates and (3) colonization rates and spore densities are additionally reduced by fertilization. A pot experiment was set up to study the effect of cropland soil inoculation using pristine fungal communities (from adjacent forests) or fertilization. AMF spore densities in soil with and without teff and root colonization by AMF and dark septate endophytes (DSE) were related to straw and grain yields. AMF and DSE colonization rates were higher after inoculation, which provides evidence that a low spore density limits teff root colonization in eroded soils. However, teff yields were significantly increased after fertilisation but not inoculation. N-P fertilization further lowered root colonization rates and spore density. We conclude that forest soils serve as a refugium for soil biota in the degraded landscape of the Ethiopian highlands. As both increased AMF and DSE increase the stress resistance of plants, their inoculation potential should be considered when developing sustainable management methods for teff.

Arbuscular mycorrhizal fungi and the associated bacterial community influence the uptake of cadmium in rice

Cadmium (Cd)-contaminated rice imposes severe health risks to human. The present study investigated the role of arbuscular mycorrhizal fungi (AMF) in sculpting the rhizospheric bacterial community, and the potential effects on the Cd uptake by rice. AMF Funneliformis mosseae (Fm) or Rhizophagus intraradices (Ri) were inoculated to rice grown in soils spiked with 0 or 10 μM Cd. Initial Cd concentration in soil was 0.18 mg/kg. AMF colonization rate, plant biomass, Cd content in rice, soil properties, rice Cd transporters (Nramp5 and HMA3) and soil bacterial community were analysed. Both AMF decreased (P < 0.05) root and shoot Cd concentrations, especially for Ri treatment. The higher relative abundance of Actinobacteria (mostly from genus Arthrobacter) observed in Ri treatment probably absorbed Cd in soil, and hence decreased the Cd availability for rice. Expression of genes Nramp5 and HMA3 in root were lower in Ri treatment, but higher in Fm treatment. The gene expressions were in line with the results of lower root Cd content in Ri treatment, and higher in Fm treatment. The present study firstly revealed that AMF can reduce rice Cd uptake by changing the expression of Cd transporters and soil bacterial community in a pot experiment. Effects of plants-bacteria-fungi interaction on both plant productivity and toxicants uptake deserved further study.

Elevated temperature reduces wheat grain yield by increasing pests and decreasing soil mutualists.

Climate warming is known to affect species' phenology, abundance, and their interactions with other species. Understanding how cultivated plants, their associated community members (including pest insects, natural enemies, soil microbes), and their interactions respond to warming to influence crop yields is critical to current and future food security. We conducted a two-year field study on the effects of elevated temperature on winter wheat growth and grain quality, insect pests, natural enemies, ground arthropods, weeds, and arbuscular mycorrhizal fungi (AMF). Elevated temperature shortened the period of wheat growth, decreased grain yield, and reduced grain quality by increasing fiber and decreasing wet gluten, protein, total soluble sugars, and starch. Elevated temperature also increased aphid abundance while decreasing AMF colonization rates. Structural equation modeling indicated that the direct negative effect of warming on wheat yield was augmented by indirect negative effects via increased aphid and weed abundances along with decreased AMF colonization. Climate change can potentially affect crop production and quality both directly and indirectly by modifying interactions with aboveground and belowground organisms. Future studies on the effects of climate change on crops should consider the responses of aboveground and belowground biotic community members and their interactions with crop plants. © 2018 Society of Chemical Industry.

Influence of Sugarcane Genotype and Soil Moisture Level on the Arbuscular Mycorrhizal Fungi Community

The relationship between sugarcane genotype and symbiosis with arbuscular mycorrhizal fungi (AMF) remains poorly understood, especially regarding different soil moisture levels. Our objective was to evaluate the effect of soil moisture on the AMF community structure, spore abundance and colonization ratio in a plantation with eight sugarcane genotypes (CTC15, CTC17, RB867515, RB92579, RB931011, RB966928, IAC5000 and NCo376). The study was carried out in Piracicaba, Sao Paulo and Brazil in an experimental plot setup in a randomized block design, with three replicates (blocks). We collected soil and root samples in a greenhouse experiment under two water replenishment levels: 100 and 50% of soil moisture at field capacity (θFC). We extracted spores and assessed the AMF root colonization ratio by using specific dyes and determining the percentage of root length colonized in the different sugarcane genotypes. In addition, we evaluated the AMF community structure by PCR and denaturing gradient gel electrophoresis. In general, the spore abundance and root colonization ratio were higher in all varieties at 100% θFC. However, the IAC5000 and RB966928 genotypes showed higher colonization levels even at 50% θFC. The AMF community structure was also influenced by soil water levels with group separations across 100 and 50% θFC. Sugarcane productivity as measured by stalk plus root dry mass was positively correlated with AMF colonization rates in 100% θFC. Thus, the water replenishment levels used in sugarcane cultivation can influence spore abundance, colonization ratios and AMF community structure in the soil. The selection of a sugarcane genotype with greater AMF association under low water replenishment levels may be a primary factor in growing sugarcane in areas with low water availability.

Arbuscular Mycorrhizal Fungi and Rhizobacteria Promote Growth of Russian Knapweed (Acroptilon repens L.) in a Cd-Contaminated Soil

Improving soil microbial activity and using microbial synergistic relations, such as arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR), are of major importance for plant growth in contaminated soils with heavy metals. In this study, growth of Russian knapweed (Acroptilon repens L.) inoculated with either AMF or PGPR was studied in a soil spiked with 0, 10, 30, 100 mg kg− 1 cadmium (Cd). AMF colonization rate in roots significantly declined by an average of 63.6% as soil Cd level increased. Similarly, shoot dry weight significantly declined as soil Cd level increased, but inoculation with either AMF or PGPR showed a promoting effect on shoot biomass compared with the non-inoculated plants. Cd concentrations in the shoots were higher in the PGPR-treated plants compared with control plants, whereas Cd concentrations in the roots were higher in the AMF-treated plants. The highest amount of Cd extraction was observed for PGPR-inoculated plants, followed by AMF-inoculated plants, and control plants. Elevated Cd level in the soil decreased the photosynthetic pigments chlorophyll a, chlorophyll b, and carotenoids, but AMF- and PGPR-treated plants alleviated this effect compared with control plants. Similarly, relative water content (RWC) of Russian knapweed plants decreased with elevated Cd level in the soil, but RWC was higher in the inoculated plants in all Cd levels in the soil. Inoculation of Russian knapweed plants with AMF and PGPR may effectively contribute to restoration of Cd-contaminated soils and can promote phytoremediation processes. Further research could focus on the effectiveness of Russian knapweed plant inoculation with AMF and PGPR in alleviating heavy metal toxicity in different soil types.