Arbuscular Mycorrhizal Root Colonization Research Articles

Influence of AM fungi and its associated bacteria on growth promotion and nutrient acquisition in grafted sapota seedling production

A study was undertaken to know the effect of co-inoculation of Arbuscular Mycorrhizal (AM) fungi and its associated bacteria on enhancing AM root colonization, growth promotion and nutrient acquisition in grafted sapota plants. The best mycorrhiza associated bacteria i.e. Pseudomonas putida (HM590707) isolated from Funneliformis mosseae spore was evaluated along with AM fungi for growth promotion and AM fungal colonization in grafted sapota plants. The combined application of P. putida along with AM fungi significantly increased plant height (39.67 %), stem girth (3.2 cm), total biomass (66.8 g plant-1), AM root colonization (73.4 %)and plant nutrient concentrations viz., N (2.52 %), P (0.18 %), K (2.90 %), Fe (428.4 ppm) and Zn (21.40 ppm) as compared to uninoculated control. This finding clearly demonstrated that grafted sapota plants can be successfully established by combined inoculation of AM fungi and its associated bacteria which have a greater impact on healthy grafted plants.

Native soil organic matter as a decisive factor to determine the arbuscular mycorrhizal fungal community structure in contaminated soils

The present study of arbuscular mycorrhizal (AM) fungi is focused on the identification of AM ecotypes associated with different plants species (Poa annua, Medicago polymorpha, and Malva sylvestris) growing in three contaminated soils with different organic matter, phosphorus, and trace element (TE; Cu, Cd, Mn, and Zn) contents. Soils were amended with biosolid and alperujo compost. Shifts in AM fungal community structure, diversity, richness, root colonization, and plant TE uptake were evaluated. Soil properties and plant species had a significant effect on AM fungal community composition as well as on root colonization. However, AM fungal diversity and richness were only affected by soil properties and especially by soil organic matter that was a major driver of AM fungal community. As soil quality increased, Glomeraceae decreased in favor of Claroideoglomeraceae in the community, AM fungal diversity and richness increased, and root colonization decreased. No effect due to amendment (exogenous organic matter) addition was found either in AM fungal parameters measured or TE plant uptake. Our results revealed that the role of TE contamination was secondary for the fungal community behavior, being the native organic matter content the most significant factor.

Phosphorus acquisition by three wheat cultivars contrasting in aluminium tolerance growing in an aluminium-rich volcanic soil

Phosphorus (P) deficiency and aluminium (Al) phytotoxicity are major limitations for crop yield in acid soils. To ameliorate such limitations, agricultural management includes application of lime and P fertilisers, and the use of Al-tolerant plant genotypes. The mechanisms of Al tolerance and P efficiency may be closely related through strategies that decrease the toxicity of the Al3+ ion and increase P availability in soils. However, the effects of soils with high Al saturation on P acquisition by wheat have been little studied under field conditions. The aim of this work was to study Al–P interactions on wheat genotypes of contrasting Al tolerance when grown under field conditions in a volcanic soil with high Al saturation (32%) and low pH (5.0). A field-plot experiment was performed with winter wheat genotypes, two Al-tolerant (TCRB14 and TINB14) and one Al-sensitive (STKI14), with application of 0, 44 and 88 kg P ha–1. At the end of tillering and after physiological maturity (90 and 210 days after sowing), plants were harvested and yield and P and Al concentrations in shoots and roots were measured. Soil acid phosphatase, root arbuscular mycorrhizal (AM) colonisation, AM spore number and soil glomalin were determined. Shoot and root production and P uptake were higher in Al-tolerant genotypes than the sensitive genotype. In addition, root AM colonisation and soil acid phosphatase activity were also higher in tolerant genotypes. By contrast, Al concentration in shoots and roots was higher in the sensitive genotype with a concomitant decrease in P concentration. Grain yield of Al-tolerant genotypes was higher than of the Al-sensitive genotype with and without P fertiliser. Overall, the Al-tolerant genotypes were more effective at P acquisition from soil as well as from P fertiliser added, suggesting that plant traits such as Al tolerance, P efficiency, and AM colonisation potential co-operate in overcoming adverse acid soil conditions.

Influence of Biochar Application and AMF Inoculation on Root Colonization and Selected Soil Chemical Properties

Screen house experiment was carried out in 2013-2014 at Federal University of Agriculture, Abeokuta. to investigate the effects of biochar application and arbuscularmycorrhizal (AM) inoculation to tomato genotype on 1) AM root colonizationand 2) selected soil chemical properties The experiment was laid out in a 2 × 5 × 2 factorial, fitted into a completely randomized design with three replications. The studies factors included tomato genotypes (Ex-Lafia and Ex-Lokoja), biochar application (0, 5, 10, 15 and 20 t ha-1) and AMF (with and without AMF).Data were subjected to analysis of variance and significant means separated using Duncan’s Multiple Range Test (P<0.05). Mycorrhizal inoculation influenced AM root colonization, and the addition of mycorrhizal had higher values (51.33%) when compared with non mycorrhizal pots (10.17%). Mycorrhizal inoculation had little or no influence on soil pH, organic carbon and available P. Biochar application generally increased AM root colonization, soil pH and available P when compared with control. The 20 t ha-1 of biochar application had improved soil properties as compared to other biochar rates. It is concluded that AMF inoculation in biochar amended soil is important. It is therefore, recommended that field studies should be done to upscale the current screen house conclusion to the field condition, and quantitatively confirm the optimum application rate for enhanced AM root colonization and soil chemical characteristics.

Effect of Biochar Application and Arbuscular Mycorrhizal Inoculation on Root Colonization and Soil Chemical Properties

Field experiment was carried out in 2013 and 2014 to investigate the effects of biochar application and arbuscular mycorrhizal (AM) inoculation on AM root colonization and selected soil chemical properties of two tomato genotypes. The experiment was laid out in a split-split plot arrangement with two tomato genotypes in the main plots, five rates of biochar applied in the sub plots and two levels of AMF inoculation in the sub-sub plots. Data were subjected to analysis of variance and significant means separated using Duncan’s Multiple Range Test (P&lt;0.05). The results indicated that mycorrhizal inoculation had little or no influence on AM root colonization, soil organic carbon, soil pH and available phosphorus. Application of 20 t ha-1 of biochar significantly increased (P&lt; 0.05) soil pH and available P compared with the control while 10 t ha-1 and 15 t ha-1 of biochar produced higher organic carbon than other rates. In conclusion, biochar increased soil pH but was not high enough as to have detrimental effect on soil properties. It is, therefore, recommended that biochar with very strongly alkaline pH should only be used in soil with low pH for improvement of soil chemical and AM root colonization.

The role of arbuscular mycorrhizal fungi in grain production and nutrition of sorghum genotypes: Enhancing sustainability through plant-microbial partnership

The responsiveness of 3 landrace (open-pollinated) sorghum cultivars and 3 modern (commercial) hybrids to arbuscular mycorrhizal (AM) fungi and commercial fertilizers were assessed. Sorghum genotypes were selected to represent a range of sorghum breeding development. This comparison was conducted to link grain production and quality with crop nutrition strategies (AM symbiosis versus fertility amendments). The open-pollinated cultivars produced an average of 206% more vegetative biomass and 285% more grain per plant, compared to commercial hybrids when grown with AM fungi and no fertilization. Furthermore, the average protein production of open-pollinated cultivars was 320% greater, compared to hybrids grown under the same low-fertility conditions. Percent AM root colonization was 149% greater in open-pollinated cultivars compared to hybrids, and across all genotypes, AM colonization was significantly correlated with total grain mineral content. Sorghum cultivars were significantly more responsive to mycorrhizal symbiosis than commercial hybrids for nutrient uptake and subsequent grain production and quality, while hybrids were significantly more responsive to fertilization.

Contribution of forest floor fractions to carbon storage and abundance patterns of arbuscular mycorrhizal fungal colonisation in a tropical montane forest

Forest floor carbon stocks, which include different components of litter, hemic and sapric materials, have not been empirically quantified in tropical montane forest, although they influence soil carbon (C) pools. To date, the contribution of arbuscular mycorrhizae in C sequestration potentials in tropical montane forests have not been clearly investigated. This study determined the amount of C stocks in the different decomposing layers of forest floor, mainly litter, hemic and sapric materials. The abundance of arbuscular mycorrhizal root colonisation differed among forest floor fractions. Forest floor was measured for depth, area density, dry mass and carbon fraction separately in Sungai Kial Forest Reserve, Pahang, Malaysia to calculate C stocks. Percentages of root colonisation in the hemic and sapric materials were investigated. The results showed that forest floor C stocks were significantly higher in hemic (5 Mg C ha−1) and sapric (7.7 Mg C ha−1) compared with the litter fragments (1.5 Mg C ha−1). Mycorrhizal root colonisation was significantly higher (75%) in the toeslope compared with the summit area in the hemic materials. Segregation of forest floor layers provided greater accuracy in forest floor C stocks reporting.

Nitrogen isotope fractionation during N uptake via arbuscular mycorrhizal and ectomycorrhizal fungi into grey alder

Arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi affect plant nitrogen (N) dynamics. Plant N isotope patterns have been used to characterise the contribution of ECM fungi to plant N uptake. By quantifying and comparing the effects of an AM and an ECM fungus on growth, N uptake and isotopic composition of one host plant grown at different relative N supply levels, the aim of this study was to improve the mechanistic understanding of natural 15N abundance patterns in mycorrhizal plants and their underlying causes.Grey alders were inoculated with one ECM fungus or one AM fungus or left non-mycorrhizal. Plants were grown under semi-hydroponic conditions and were supplied with three rates of relative N supply ranging from deficient to luxurious.Neither mycorrhizal fungus increased plant growth or N uptake. AM root colonisation had no effect on whole plant δ15N and decreased foliar δ 15N only under N deficiency. The roots of these plants were 15N-enriched. ECM root colonisation consistently decreased foliar and whole plant δ15N.It is concluded, that both mycorrhizal fungi contributed to plant N uptake into the shoot. Nitrogen isotope fractionation during N assimilation and transformations in fungal mycelia is suggested to have resulted in plants receiving 15N-depleted N via the mycorrhizal uptake pathways. Negative mycorrhizal growth effects are explained by symbiotic resource trade on carbon and N and decreased direct plant N uptake.

Arbuscular mycorrhizal inoculation in coastal sage scrub restoration

We tested the hypothesis that field applications of arbuscular mycorrhizal (AM) inocula would increase root colonization and plant performance in a coastal sage scrub (CSS) restoration project in Southern California. We applied commercial or native inocula (from nearby reference shrublands) as we seeded plots with native shrubs, forbs, and grasses. A control treatment was seeded but received no inocula. After 6 months, AM root colonization did not differ significantly among treatments. Likewise, neither inoculum type significantly altered shoot biomass of native shrubs and forbs at 6 months, or density of adult and seedling shrubs at 10 months. Notably, shoot height at 10 months was shorter in plots treated with commercial inoculum compared with the controls. In addition, flower and flower bud production by Salvia columbariae did not significantly respond to either inoculum type. Altogether, we found no evidence that AM inoculation improved restoration success in our CSS system.

Above- and below-ground responses of native and invasive prairie grasses to future climate scenarios

More intense and frequent droughts, coupled with elevated temperatures, are projected for grasslands worldwide. Although it has been suggested that alterations in temperature and precipitation will increase the success of biological invasions, studies that combine these climate change scenarios are limited. These changes in climate may increase the success of non-native, invasive plant species directly, as these species often possess traits that are favored by variable climates, or indirectly through negative impacts on native vegetation or alterations in soil microbial communities, such as arbuscular mycorrhizal (AM) fungi. The goal of our research was to assess above- and below-ground production and mycorrhizal fungal abundance of functionally similar native and invasive non-native grass species under projected climate-change scenarios. We assessed plant biomass, intra-radical AM root colonization, and relative abundance of extra-radical fungal biomass of two native (Schizachyrium scoparium (Michx.) Nash, Pascopyrum smithii (Rydb.) Á.Löve) and two invasive (Bothriochloa ischaemum (L.) Keng, Bromus inermis Leyss.) grass species subjected to increased temperature and decreased soil water availability. Regardless of temperature or soil moisture, the invasive grasses in our study displayed greater seedling growth as compared with paired native species. Invasive grasses were also generally characterized by greater intra-radical colonization by AM fungi, compared with native species. Our data suggest that invasive grasses will continue to be problematic and successfully out-compete native grasses following increased temperatures and reduced water availability, as projected by climate-change models.

Influence of season and edaphic factors on endorhizal fungal associations in subtropical plantation forest trees of Northeastern India

Investigations on arbuscular mycorrhizal (AM) and dark septate endophyte (DSE) fungi are limited in trees of subtropical forests compared to other terrestrial ecosystems. We assessed the seasonal dynamics of endorhizal fungal symbioses in four dominant tree species (Alnus nepalensis, Castanopsis hystrix, Emblica officinalis, Schima wallichii) in two plantation forest stands of Northeastern India, a biodiversity hotspot part of the Indo-Burma region. All tree species examined had a dual association of AM and DSE fungi and such fungal symbioses are reported for the first time in A. nepalensis, C. hystrix and S. wallichii. Intermediate-type AM morphology was common in three tree species, while Paris-type AM morphology was found in S. wallichii. Colonization of AM and DSE fungi varied significantly across tree species and seasons. A total of 18 AM fungal spore morphotypes were isolated from the air-dried natural rhizosphere soils and trap culture experiments. Spore density of AM fungi was highest in summer, whereas AM colonization in roots was highest during the rainy season. In contrast, root colonization with DSE fungi was highest during summer, except for E. officinalis. A significant negative correlation occurred between certain AM fungal and soil variables. In contrast, DSE fungal measures were not correlated to any of the soil properties examined. Correlation analysis indicated a certain degree of competition between AM and DSE fungi. Occurrence of AM and DSE fungal associations in economically important indigenous tree species indicates the possibility of utilizing them in future conservation programs.

Phosphorus Fertilization Effect on Timothy Root Growth, and Associated Arbuscular Mycorrhizal Development

Root architecture and mycorrhizal associations are plant traits that determine soil P uptake by plants. However, the response of these important plant traits to mineral P fertilization under grasslands production is poorly understood. We assessed the effect of P fertilization at 0, 20, or 40 kg P ha−1 applied in the spring of each year since 2010 on root attributes, arbuscular mycorrhizal (AM) root colonization, plant growth, and plant P concentration in timothy (Phleum pratense L.) swards seeded in 2009 on a Labarre clay loam in Normandin, QC, Canada. Soil cores for root samples (height of 7.5 cm and inner diameter of 8 cm) were collected in June 2013 after the first harvest and in August 2014 after the second harvest. The results showed that P application increased dry matter (DM) yield and shoot P uptake at the first harvest time but not at the second. Shoot P concentration increased with increasing P application, particularly in August 2014. Phosphorus fertilization had no significant influence on root architectural attributes, colonization by hyphae or arbuscules, or total AM root colonization at both sampling times. However, in August 2014, AM vesicle density in roots was significantly greater with 40 kg P ha−1 than without P fertilization. We conclude that timothy shoot and root growth varied with sampling time but that root architectural traits and the AM colonization of timothy roots were influenced little by P fertilization in eastern Canada.

Arbuscular mycorrhizal fungal diversity in wheat agro-ecosystems in Southern Chile and effects of seed treatment with natural products

Arbuscular mycorrhizal (AM) fungi are important for P uptake in Andisols cultivated with wheat. We assessed AM fungal diversity in field experiments established with wheat cultivated after AM host plants and non-host plants at three locations of the Araucania Region. Wheat seed was treated with two natural products: Fosfobio (FOS), mixture of P-solubilizing bacteria and N2-fixing bacteria; and Myconate (MYC), product containing formononetin. For investigations of AM fungal diversity, soil samples were taken before planting and after harvest of wheat. The morphological spore analyses resulted in 26 species, belonging to 10 families and 16 genera; 5 species belonged to Acaulospora (31.2% of total), and 3 to Claroideoglomus (18.8%). Claroideoglomus claroideum was the prevalent while Ambispora leptoticha, Dominikia aurea, and Glomus badium presented the lowest frequency.The AM fungal species distribution was strongly dependent on the location, and richness at planting of wheat was higher when a non-host for AM fungi had been grown before. There appeared to be a tendency that through wheat cultivation, the richness of AM fungal species decreased from time of planting to harvest when the pre-crop was a non-host; when the pre-crop was AM host there was no apparent decrease in AM species richness through wheat cultivation. Natural products did not significantly influence grain yields. However, there was a tendency that MYC increased average grain yields by 7%. It is discussed that increased AM root colonization, as by MYC and improved P-uptake by AM fungi is more important than inoculation of seed with P-solubilizing microbes.

Arbuscular Mycorrhizal symbiosis in four Al-tolerant wheat genotypes grown in an acidic Andisol

Arbuscular mycorrhizal (AM) fungi play an important role in protecting host plant against phytotoxic aluminum (Al) in soil. The aim of this work was to analyze the effect of AM fungi native from acid soil on the growth of four Al-tolerant wheat (Triticum aestivum L.) genotypes. A greenhouse experiment was conducted using three near isogenic Chilean wheat genotypes (‘Crac’, ‘Invento’ and ‘Otto’) and one of recognized Al-tolerance (‘Atlas 66’) which were grown in an acid Andisol with 34% Al-saturation. The plant dry biomass and root colonization were determined at six early growth stages and AM spore density, glomalin (as GRSP) and acid phosphatase (P-ase) activity were analyzed at two stages; i) 11 days after sowing -DAS-, and at 60 DAS. Results showed that in all genotypes AM root colonization was not inhibited in spite of high soil Al saturation in the soil and a significant root colonization degree was observed at the first phenological stage mainly in the native wheat genotypes. Also, ‘Crac’ and ‘Invento’ genotypes showed the highest densities of AM spores and GRSP production. All wheat cultivars increased the P-ase activity overtime. Root biomass correlated positive and significantly with root colonization (r=0.71; P<0.001) and inversely with AM spores (r=-0.61; P<0.001). ‘Atlas 66’ showed a high adaptability to grow in acid conditions but produced the lesser amounts of AM propagules, which suggest that this genotype would show Al-tolerance mechanisms not fully associated to AM symbiosis as the Chilean wheat cultivars do. In conclusion, the higher early root colonization, AM spores and GRSP production associated to native wheat genotypes could indicate that AM symbiosis play a principal role in the Al tolerance capacity of T. aestivum developed in those soils with high Al levels and fungal native populations adapted to this conditions.

Arbuscular mycorrhizal symbiosis induces strigolactone biosynthesis under drought and improves drought tolerance in lettuce and tomato.

Arbuscular mycorrhizal (AM) symbiosis alleviates drought stress in plants. However, the intimate mechanisms involved, as well as its effect on the production of signalling molecules associated with the host plant-AM fungus interaction remains largely unknown. In the present work, the effects of drought on lettuce and tomato plant performance and hormone levels were investigated in non-AM and AM plants. Three different water regimes were applied, and their effects were analysed over time. AM plants showed an improved growth rate and efficiency of photosystem II than non-AM plants under drought from very early stages of plant colonization. The levels of the phytohormone abscisic acid, as well as the expression of the corresponding marker genes, were influenced by drought stress in non-AM and AM plants. The levels of strigolactones and the expression of corresponding marker genes were affected by both AM symbiosis and drought. The results suggest that AM symbiosis alleviates drought stress by altering the hormonal profiles and affecting plant physiology in the host plant. In addition, a correlation between AM root colonization, strigolactone levels and drought severity is shown, suggesting that under these unfavourable conditions, plants might increase strigolactone production in order to promote symbiosis establishment to cope with the stress.

Phosphorus fertilization of a grass-legume mixture: Effect on plant growth, nutrients acquisition and symbiotic associations with soil microorganisms

ABSTRACTAdding P on Lotus tenuis and Festuca arundinacea, pure or mixed, on growth, nitrogen (N) and phosphorus (P) acquisition and associations with soil microorganisms was studied to investigate the establishment of Lotus for competing with Festuca. Triple-superphosphate was applied on a Typic Natraquoll where Lotus grows spontaneously. Biomass, N-P uptake, arbuscular mycorrhizal colonization and rhizobia nodulation were measured. Lotus achieved the highest biomass, N-P uptake in fertilized stands and Festuca the lowest in fertilized and non-fertilized stands. Mycorrhizal colonization decreased with P-fertilization in both plants. Rhizobia nodules in Lotus showed little changes with P-fertilization. In mixed fertilized-stands, Lotus promoted the growth, N-P uptake of Festuca. P-fertilization increases the ability of Festuca to compete with Lotus for available-P in soil. Lotus improves nutrient cycling, maintains high level of rhizobia nodules and arbuscular mycorrhizal colonization in roots. Adding P to limited N-P environments depress grasses growth to compete with legumes for resources.

Biochar and Compost Increase Crop Yields but the Effect is Short Term on Sandplain Soils of Western Australia

Sandplain soils on the south coast of Western Australia have low inherent fertility, which is mainly due to poor nutrient retention caused by insufficient clay and organic colloidal material. Previous research has shown the benefits in nutrient levels and retention from adding clay to sandplain soils; however, there is almost no information on the addition of organic amendments. A field experiment was established at the Esperance Downs Research Station, Western Australian, in May 2010, to assess the effects of wheat straw (WS) and chicken manure (CM) biochars and compost with and without phosphorus (P) addition on soil properties and crop production over five growing seasons. The five seasons alternated between winter and summer crops. The CM and WS biochar and compost treatments significantly increased crop yields and P uptake in 3, 2 and 1 of the five seasons, respectively. The yield increases (P « 0.05) were no more than 8%. By the end of the third season, no differences in crop yields were found that could be attributed to the organic amendments. The addition of P increased crop yields in each winter cropping season. Phosphorus addition explained more than 30% of the variation in crop yields. Despite marginal P levels and summer drought conditions, arbuscular mycorrhizal root colonisation was not affected by the organic amendments. There were no significant interactions between the organic amendments and P addition in terms of crop yields, P uptake or P uptake efficiency. We conclude that much of the effect of the organic amendments was due to direct nutrient addition which dissipated over time.

Effect of conventional and organic orchard floor management practices on arbuscular mycorrhizal fungi in a ‘Cripp’s Pink’/M7 apple orchard soil

Arbuscular mycorrhizal (AM) fungi are key components of agricultural soil–plant systems, which may be affected by agricultural practices. In organically managed (ORG) orchards, nutrients are supplied in the form of compost, and weeds are suppressed with mulches, whereas synthetic fertilizers and herbicides are used for these respective purposes in conventional (CON) orchards. The effects of ORG and CON orchard floor management practices on native AM fungi in apple orchards were investigated in a randomized field trial. AM root colonization, spore abundance, infectivity potentials and soil glomalin contents were determined in the 0–30cm soil depth interval, in tree rows, over consecutive seasons. Root colonization was higher in the ORG than the CON treatments, but intermediate where straw mulch was substituted for green work-row covers. Glomalin levels were not affected by the treatments. Root colonization by AM fungi increased with increasing soil pH, P, C, K, Zn, and Mn concentrations, but were suppressed by Cu. Colonization correlated positively with leaf P, Ca and Mg, and with stem circumference, but negatively with leaf N and yield. ORG orchard floor management practices therefore, promoted functional AM associations more effectively than CON practices.

Role of arbuscular mycorrhizal fungi in alleviating the adverse effects of acidity and aluminium toxicity in zucchini squash

The aim of the current research was to assess whether arbuscular mycorrhizal (AM) inoculation would give an advantage to overcome acidity and aluminium (Al) toxicity problems and to study the changes induced by AM at agronomical and physiological level. A greenhouse experiment was carried out, to determine yield, growth, fruit quality, SPAD index, electrolyte leakage, and mineral composition of zucchini squash (Cucurbita pepo L.) inoculated (+AM) and noninoculated (−AM) with arbuscular mycorrhizal and cultured in pots filled with quartziferous sand. Plants were supplied with nutrient solutions having different pH and aluminium concentration (pH 6.0, pH 3.5 or pH 3.5+Al). The low pH treatment had the same nutrient composition plus HCl, whereas the aluminium treatment (pH 3.5+Al) was induced by adding 1.0mM of AlCl3·6H2O. The AM root colonization was higher in the control treatment (pH 6.0; 48.5%), followed by pH 3.5 (23.4%), and finally in pH 3.5+Al treatment (17.1%). Significant depression of yield, biomass, SPAD index, leaf area, N, P, Mg, Fe, and Zn concentration in leaf tissue was observed in response to low pH level with more detrimental effects with pH 3.5+Al. The inoculated plants under acidity and Al conditions had higher total, marketable yield, and total biomass than noninoculated plants. Zucchini-fruit quality, in particular fruit dry matter, total soluble-solids content, P, and Fe concentration, was improved by mycorrhizal colonization. Mycorrhized zucchini plants grown under acidity and Al conditions had a higher macronutrient concentration in leaf tissue compared to noninoculated plants. The better crop performance in inoculated plants were related to the capacity of maintaining higher SPAD index, lower electrolyte leakage, and better nutritional status (high N, P, K, Ca, Mg, Fe, Zn, and B and low Al accumulation) in response to Al stress with respect to −AM plants.

Effects of dual inoculation with arbuscular mycorrhizal fungi and rhizobia on Acacia senegal (L.) Willd. seedling growth and soil enzyme activities in senegal

Acacia senegal (L.) Willd. is a multipurpose legume that is economically and ecologically important in Sahelian areas, especially in Senegal. It has long been used for arabic gum production. However, drought and overexploitation lead to decreased soil fertility and tree productivity. An experiment was conducted to examine the response of A. senegal seedlings to inoculation with mixed arbuscular mycorrhizal fungi (Glomus fasciculatum, Rhizophagus irregularis and Glomus verriculosum) and rhizobial strains (ORS 3574, ORS 3593, ORS 3607 and ORS 3628) in glasshouse conditions. After 6 months of culture under non-sterilized field soil from Dahra (northern part of Senegal), plant height, arbuscular mycorrhizal root colonization rate and soil acid phosphatase activity were significantly enhanced by the combined inoculation of arbuscular mycorrhizal fungi (AMF) and rhizobia. However, plant biomass, soil spore density and hyphal length were significantly improved by the single inoculation with mycorrhizal or rhizobial strains. The number of nodules was higher for rhizobial inoculated plants. No significant increase in shoot nutrient contents was observed after inoculation. The microbial inoculation enhances the soil acid phosphatase activity whereas no positive effect was noticed on soil total microbial activity. These results indicate that the single inoculation with AMF or rhizobia improves A. senegal seedling growth under this non-sterilized field soil better than the dual inoculation. It is suggested that, for the success of a dual inoculation, a careful selection of effective combinations of microsymbionts is necessary to enhance plant growth and soil bio-functioning and for restoration of soil fertility in a given environment.