Calcium oxalate accumulation and soil weathering in mats of the hypogeous fungus Hysterangium crassum

Fungal mats of Hysterangium crassum (Tul. and Tul.) Fischer occupied a mean of 9.6% of the upper 10 cm of soil developed under a 40–65 yr old stand of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in Oregon. This hypogeous basidiomycete exudes large amounts of oxalic acid, some of which precipitates with Ca in microscopic crystals of calcium oxalate, resulting in a mean CaC₂O₄ content of 82g m^?2 for the entire soil. Soil oxalate concentration was significantly greater within fungal mats (P < 0.01) and soil pH was significantly lower (P < 0.01) than in soil adjacent to mats. The quantity of Ca present as CaC₂O₄ is 0.5 the amount of exchangeable Ca in the soil and exceeds the mass of Ca lost annually in runoff. Scanning electron micrographs show intense chemical weathering, attributable to oxalate attack, in the immediate vicinity of hyphae. X-ray diffraction patterns of clay indicate bulk weathering is more intense within the fungal mats than in adjacent uncolonized soil.     

Nitrogen capture by grapevine roots and arbuscular mycorrhizal fungi from legume cover-crop residues under low rates of mineral fertilization

The influence of mineral fertilization on root uptake and arbuscular mycorrhizal fungi-mediated ¹⁵N capture from labeled legume (Medicago polymorpha) residue was examined in winegrapes (Vitis vinifera) in the greenhouse, to evaluate compatibility of fertilization with incorporation of cover-crop residue in winegrape production. Plants grown in marginal vineyard soil were either fertilized with 0.25× Hoagland’s solution or not. This low fertilization rate represents the deficit management approach typical of winegrape production. Access to residue in a separate compartment was controlled to allow mycorrhizal roots (roots + hyphae), hyphae (hyphae-intact), or neither (hyphae-rotated) to proliferate in the residue by means of mesh core treatments. Leaves were weekly analyzed for ¹⁵N. On day 42, plants were analyzed for ¹⁵N and biomass; roots were examined for intraradical colonization; and soils were analyzed for ¹⁵N, inorganic N, Olsen-P, X-K, and extraradical colonization. As expected, extraradical colonization of soil outside the cores was unaffected by mesh core treatment, while that inside the cores varied significantly. ¹⁵N atom% excess was highest in leaves of roots + hyphae. In comparison, leaf ¹⁵N atom% excess in hyphae-intact was consistently intermediate between roots + hyphae and hyphae-rotated, the latter of which remained unchanged over time. Fertilization stimulated host and fungal growth, based on higher biomass and intraradical colonization of fertilized plants. Fertilization did not affect hyphal or root proliferation in residue but did lower %N derived from residue in leaves and stems by 50%. Our results suggest that even low fertilization rates decrease grapevine N uptake from legume crop residue by both extraradical hyphae and roots.     

Palatability of microfungi to soil arthropods in relation to the functioning of arbuscular mycorrhizae

We investigated the feeding preferences of six species of mites and collembolans for three fungi commonly associated with roots of Acer saccharum (Glomus macrocarpum, Alternaria alternata and Trichoderma harzianum), from a maple-forest soil in southern Ontario, Canada. Experiments were also conducted in vitro to determine animal feeding responses to (1) increasing quantities of hyphal biomass, (2) the presence of root vs. litter fungal substrates, and (3) hyphae of different widths of Glomus macrocarpum. The results indicate that arthropods prefer to graze in the litter region rather than in the deeper soil layers. Under ideal moisture/temperature conditions, animals are forced to the lower regions by interspecific interactions. They prefer to graze on hyphae of conidial fungi rather than on those of arbuscular mycorrhizal fungi. When arbuscular mycorrhizal fungal hyphae are grazed, there is a clear preference for the narrower hyphae, which are those further away from the root. The thicker hyphal segments, commonly found connecting absorptive hyphal fans to roots, were less preferred. These data are not consistent with the hypothesis that microarthropods are detrimental to arbuscular mycorrhizal associations, and suggest that Glomalean fungi may have evolved mechanisms to deter grazing by microarthropods.     

Can the arbuscular mycorrhizal fungus Glomus intraradices actively mobilize P from rock phosphates?

Plants colonized by arbuscular mycorrhizal (AM) fungi have been shown to respond positively to the application of insoluble forms of inorganic phosphorus (P) such as rock phosphates (RPs). The mechanism(s) underlying such responses remain(s) unknown and although it has been hypothesized, there is no experimental support for the production of chelating agents by AM fungal hyphae. Here we investigate whether AM fungi can solubilize P from RPs and transfer it to plant roots. Using root-organ cultures of Daucus carrota L. inoculated or not with Glomus intraradices Schenk & Smith and containing P from different RP sources, we predicted that: (1) roots inoculated with G. intraradices would take up more P than those uninoculated; that (2) the amount of P taken up by roots through G. intraradices would be positively correlated with the RP reactivity; and that (3) G. intraradices would have access to RP through localized alterations of pH and/or by the production of organic acid anions that may act as chelating agents. The RP reactivity was positively correlated with P uptake. However, mycorrhizal roots grew initially slower and did not respond differently to any P treatment than those uninoculated. There was no evidence of localized changes in pH in proximity of G. intraradices hyphae, indicating that responses to RP by mycorrhizal plants observed in previous studies do not appear to result from the release of H⁺ ions alone or in combination with organic acid anions.     

丛枝菌根对三叶草根际磷酸酶活性的影响

以三叶草为材料,利用三室隔网培养方法,探讨了取自肥料长期定位试验中多年施用与不施用有机肥的田间小区土壤上,接种菌根菌（G.mosseae）对根际土壤酸性和碱性磷酸酶活性的影响。植物生长9周后,收获测定菌丝生长室土壤酸性磷酸酶和碱性磷酸酶活性,并对磷酸酶产生位点进行细胞化学定位。结果表明,接种丛技菌根菌对根际土壤酸性和碱性磷酸酶活性均有增强作用,但作用程度在有机服小区土壤上要大于无机肥小区土壤。根际土壤酸性磷酸酶原位化学定位结果表明,菌丝周围有明显的酸性磷酸酶的反应产物,说明报外丛枝菌根菌丝能直接向外分泌磷酸酶。     

不同氮磷比例营养液对AM真菌生长发育的影响

温室条件下,研究不同氮磷比例营养液对丛枝菌根(Arbuscular.mycorrhizae,AM)真菌(Glomus.mosseae)生长发育的影响。结果表明:在一定磷水平条件下增加氮的水平,有利于菌根真菌的生长发育,但超过一定水平则会抑制菌根真菌的生长发育,说明氮水平也会影响菌根真菌的生长发育,这种影响与氮磷比例有关。综合比较菌根长度、根外菌丝量及孢子数三项指标,在20%浓度Hoagland营养液的基础上,将氮磷比例提高到4∶2有利真菌生长。在AM菌剂生产中,通过营养液中氮磷比例的调控能获得较大数量的侵染根段、菌丝及孢子等繁殖体。     

Effects of mycorrhizal roots and extraradical hyphae on N uptake from vineyard cover crop litter and the soil microbial community

The objectives of this study were to evaluate the contribution of arbuscular mycorrhizal (AM) fungal hyphae to ¹⁵N uptake from vineyard cover crop litter (Medicago polymorpha), and to examine the soil microbial community under the influence of mycorrhizal roots and extraradical hyphae. Mycorrhizal grapevines (Vitis vinifera) were grown in specially designed containers, within which a polyvinyl chloride (PVC) mesh core was inserted. Different sizes of mesh allowed mycorrhizal roots (mycorrhizosphere treatment) or extraradical hyphae (hyphosphere treatment) to access dual labeled ¹⁵N and ¹³C cover crop litter that was placed inside the cores after 4 months of grapevine growth. Mesh cores in the bulk soil treatment, which served as a negative control, had the same mesh size as the hyphosphere treatment, but frequent rotation prevented extraradical hyphae from accessing the litter. Grapevines and soils were harvested 0, 7, 14, and 28 days after addition of the cover crop litter and examined for the presence of ¹⁵N. Soil microbial biomass and the soil microbial community inside the mesh cores were examined using phospholipid fatty acid analysis. ¹⁵N concentrations in grapevines in the hyphosphere treatment were twice that of grapevines in the bulk soil treatment, suggesting that extraradical hyphae extending from mycorrhizal grapevine roots may have a role in nutrient utilization from decomposing vineyard cover crops in the field. Nonetheless, grapevines in the mycorrhizosphere treatment had the highest ¹⁵N concentrations, thus highlighting the importance of a healthy grapevine root system in nutrient uptake. We detected similar peaks in soil microbial biomass in the mycorrhizosphere and hyphosphere treatments after addition of the litter, despite significantly lower microbial biomass in the hyphosphere treatment initially. Our results suggest that although grapevine roots play a dominant role in the uptake of nutrients from a decomposing cover crop, AM hyphae may have a more important role in maintaining soil microbial communities associated with nutrient cycling.     

Responses of directly seeded wetland rice to arbuscular mycorrhizal fungi inoculation

The mycorrhizal enhancement of plant growth is generally attributed to increased nutrients uptake. A greenhouse experiment was conducted to investigate the effect of arbuscular mycorrhizal fungi (AMF) inoculation on the growth and nutrient uptake of directly seeded wetland rice. Seeds were germinated and inoculated with arbuscular mycorrhizal fungi or left uninoculated. The plants were grown at 60% of ‐0.03 MPa to establish the mycorrhizas. After 5 weeks, half of the pots were harvested and the rest were flooded with deionized water to maintain 3–5 cm of standing water until harvesting (122 days after sowing). Mycorrhizal fungal colonization of rice roots was 36.2% at harvest. Mycorrhizal fungi inoculated rice seedlings grew better compared to uninoculated seedlings and had increased grain yield (10%) at the harvesting stage. Shoot and root growth were effectively increased by AMF inoculation at the harvesting stage. The nitrogen (N) and phosphorus (P) acquisition of direct seeding wetland rice were significantly increased by AMF inoculation. The AMF enhanced N and P translocation through the hyphae from soils to roots/shoots to grains effectively.     

Mycorrhizal inoculation effect in Acacia mangium grown in an acid oxisol amended with gypsum

Glomus aggregatum and Acacia mangium were interacted in an acid manganese (Mn)‐rich oxisol unamended or amended with hydrated lime [Ca(OH)₂] or gypsum (CaSO₄) at soil phosphorus (P) concentrations considered optimal for mycorrhizal host growth. Vesicular‐arbuscular mycorrhizal fungal (VAMF) colonization as well as VAMF function was significantly curtailed if soil was unamended with gypsum or lime. The highest mycorrhizal inoculation effect (MIE) was observed in the soil treated with gypsum at the rate of 0.32 g of calcium (Ca)/kg followed by the limed soil. Higher concentrations of gypsum deleteriously affected VAMF infectivity and effectivity. The first increment of gypsum compensated for part of the VAMF colonization and for all of the mycorrhizal inoculation effect that was lost due to low pH. The better MIE observed in the gypsum treated soil compared to that which was amended with lime suggests that the sensitivity of the acacia‐VAMF association to soil acidity was more a function of Ca inadequacy than it was of pH or associated increases in Mn concentration.     

Mycorrhizal colonization associated with roots of field-grown maize does not decline with increasing plant-available phosphorus

Maize roots are colonized by arbuscular mycorrhizal fungi, but less mycorrhizal symbiosis is expected as the plant-available phosphorus (P) concentration of soil increases, based on greenhouse and growth bench experiments. The objective of this study was to evaluate maize root colonization by arbuscular mycorrhizal fungi in a sandy loam soil with a gradient of plant-available P concentrations resulting from P fertilizer inputs. The field experiment received inorganic and organic P fertilizers for 3 years, and this created a 20-fold difference in the plant-available P concentration, from 12 to 204 mg Mehlich-3 extractable P kg⁻¹. The proportion of maize roots colonized with arbuscular mycorrhizal fungi increased from 26 ± 2% during vegetative growth (V8 and VT growth stages) to 46 ± 2% in the reproductive R2 and R6 stages. The P fertilizer input did not affect maize root colonization by arbuscular mycorrhizal fungi. More arbuscular mycorrhizal fungi colonization of maize roots occurred in soil with increasing plant-available P concentrations (r = .12, p = .05, n = 237), and this was associated with greater P uptake in the maize shoots (r = .53, p < .001, n = 240). We conclude that the root-mycorrhizal symbiosis was more strongly related to maize growth than the plant-available P concentration under field conditions.     

Mycorrhizal status of plant species colonizing a magnesite mine spoil in India

Summary The present study reports the vesicular arbuscular mycorrhizal fungal association with 14 plant species colonizing a magnesite mine spoil in Salem, Tamil Nadu state, India. The soil was poor in Olsen-available P (5–45 kg/ha^-1). Hyphal, arbuscular and vesicular infection was noticed. Infection ranged from 32 to 82%. Thirteen VAM fungal species were identified. Spores of Glomus fasciculatum and Gigaspora gigantea were commonly found in the magnesite mine spoil.     

A mycorrhizal fungus grows on biochar and captures phosphorus from its surfaces

Biochar application to soils has potential to simultaneously improve soil fertility and store carbon to aid climate change mitigation. While many studies have shown positive effects on plant yields, much less is known about the synergies between biochar and plant growth promoting microbes, such as mycorrhizal fungi. We present the first evidence that arbuscular mycorrhizal (AM) fungi can use biochar as a physical growth matrix and nutrient source. We used monoxenic cultures of the AM fungus Rhizophagus irregularis in symbiosis with carrot roots. Using scanning electron microscopy we observed that AM fungal hyphae grow on and into two contrasting types of biochar particles, strongly attaching to inner and outer surfaces. Loading a nutrient-poor biochar surface with nutrients stimulated hyphal colonization. We labeled biochar surfaces with ³³P radiotracer and found that hyphal contact to the biochar surfaces permitted uptake of ³³P and its subsequent translocation to the associated host roots. Direct access of fungal hyphae to biochar surfaces resulted in six times more ³³P translocation to the host roots than in systems where a mesh prevented hyphal contact with the biochar.We conclude that AM fungal hyphae access microsites within biochar, that are too small for most plant roots to enter (<10 μm), and can hence mediate plant phosphorus uptake from the biochar. Thus, combined management of biochar and AM fungi could contribute to sustainable soil and climate management by providing both a carbon-stable nutrient reservoir and a symbiont that facilitates nutrient uptake from it.     

Contribution of Roots and Mycorrhizal Hyphae on Phosphorus Efficiency of Maize (Zea mays,L.) Genotypes Grown on Calcareous Soil—A Mechanistic Modeling Approach

ABSTRACT

This work was conducted to study phosphorus (P) efficiency of two maize genotypes (Zea mays, L.) in calcareous soil grown in potted soil with two levels of P in soil by adding 40 and 270 mg P/kg soil. Half of the pots were inoculated with arbuscular mycorrhizal fungi (AMF) (Rhizoglomus irregulare). The maize genotypes were harvested two times at 35 and 50 days after transplanting. The plant dry matter, root length and Plant P uptake of maize genotype Hagen 1 without mycorrhizal fungi (AMF) increased significantly compared with Hagen 9 at a low P level. In contrast, there was no significant difference between two maize genotypes inoculated with AMF under the same P level. The predicted value increased rapidly with increasing P levels from about 70% up to 97% in both maize genotypes with and without mycorrhizal fungi. At a low P level, the mycorrhizae hyphae contributed by about 31.6% and 30.2% of the predicted total P uptake in maize genotype Hagen 1 and Hagen 9, respectively. The results of this study suggested that the P-inefficient genotype Hagen 9 improved with inoculation with mycorrhizal fungi under a low P level at the same conditions of this experiment. Also, root growth system and mycorrhizal hyphae length would be a suitable plant parameter for studying P efficient maize genotypes, especially under limited P supply. The current study clearly pointed out that the mechanistic simulation model (NST 3.0) provides useful tools for studying the role of AMF in P uptake of plant.     

Effects of fungicides on arbuscular mycorrhizal fungi: differential responses in alkaline phosphatase activity of external and internal hyphae

 The effect of four fungicides on alkaline phosphatase (ALP) activity in internal and external hyphae of an arbuscular mycorrhizal (AM) fungus was examined. Four-week-old plants were treated with an aqueous solution of the fungicides and then harvested 3 days later. Fungicides were applied at a low and a high level corresponding to 1 and 100 times the recommended field application dose. The fungicides were the two abundantly used sterol inhibitors, fenpropimorph and propiconazole, as well as a commercial mixture of them. Benomyl served as a positive control, as this fungicide is known for its deleterious effect on AM fungi. At harvest, roots and hyphae extracted from the soil were stained for ALP activity. Benomyl inhibited fungal ALP activity of both internal and external hyphae at the low application level (1 μg g^–1 soil) corresponding to the recommended field dose. Fenpropimorph had an intermediate effect, inhibiting both internal and external hyphae but only at the high application level (125 μg g^–1 soil). Propiconazole decreased the activity of the external hyphae at the low application level (0.21 μg g^–1 soil) but did not affect the internal activity at any application level. The effect of Tilt Top was similar to that of fenpropimorph. The results showed that the external hyphae were more sensitive than internal hyphae to application of fungicides. Received: 26 May 1999     

Glomus-wetland rice mycorrhizas influenced by nursery inoculation techniques under high fertility soil conditions

 We investigated the effect of nursery inoculation techniques on mycorrhizal colonization and sporulation, growth responses, and nutrient (N and P) uptake to determine the suitable nursey inoculation method of wetland rice (Oryza sativa L.) under high-fertility soil conditions. Seedlings were produced in dry-nursery (DN, watered to 60% of –0.03 MPa) and wet-nursery (WN, 3–5 cm water from the soil surface) conditions with or without arbuscular mycorrhizal fungal (Glomus spp.) inoculation. Soil was γ-ray sterilized before use in this experiment. Mycorrhizal fungal colonization was 56% in DN and 23% in WN plants at 6 weeks of growth. The arbuscular mycorrhizal fungal colonization was significantly higher in plants of DN origin than in WN plants after transplantation to the pots, irrespective of growing stages. Mycorrhizal colonization was significantly decreased to 28% in DN plants and to 25% in WN plants at harvest. The grain yield was significantly influenced by nursery conditions. N and P acquisition of wetland rice plants inoculated with Glomus spp. was significantly greater than that of non-inoculated plants at maturity, especially in those originating from DN conditions. P translocation from shoots to grain was accelerated by mycorrhizas. Received: 6 April 1997     

不同AM菌根菌分泌的磷酸酶对根际土壤有机磷的影响

以三叶草为材料,利用3室隔网培养方法,研究了4种AM菌根菌侵染三叶草后对根际土壤酸性和碱性磷酸酶活性以及菌丝酶活性对土壤有机P的影响。结果表明,接种AM菌根菌 (9周) 对根际土壤酸性和碱性磷酸酶活性均有增强作用,但作用强度主要取决于菌丝在土壤中的生长状况,Glomus属菌根菌在整个菌丝室 (0~6cm) 都影响土壤磷酸酶的活性,其活性在整个菌丝室中都比Gigaspora的高。同一属不同种的根际土壤磷酸酶活性差异不大。AM菌根根际土壤磷酸酶对土壤有机P的降解有很强的促进作用。     

Variation of Wheat Genotypes in Calcareous Soil as Affected by Root Growth and Mycorrhizal Hyphae– A Mechanistic Modeling Approach

ABSTRACT

This experiment aimed to study phosphorus efficiency of six wheat genotypes (Triticum aestivum) inoculated with arbuscular mycorrhizal fungi (AMF) and to quantify the contribution of root and mycorrhizal hyphae length to P uptake by using NST 3.0 model. The results showed that all wheat genotypes with AMF (except V4) attained more than 80% of the maximum shoot yield. NST 3.0 predicted approximately 49% and 30% of observed P uptake for V4 with and without mycorrhizae, respectively, at the lowest P level. Additionally, the predicted values of P uptake increased rapidly with increasing P levels by up to 90% and 89% with and without mycorrhizae, respectively, at the highest P level. The model predicted 58% and 43% of the observed P uptake for V6 with and without mycorrhizae, respectively, at the lowest P level and increased up to 98% and 95% respectively at the highest P level. Soil P depletion zones of plants without mycorrhizal fungi (V4 and V6) did not extend as far as those of plants with mycorrhizal fungi. In conclusion, we recommend that V6 (Gemmeiza12) is suitable for growth in calcareous soil with or without mycorrhizal fungi inoculation (highly P efficient). The results of this study suggest that root growth and mycorrhizal hyphae length are the main parameters suitable for selecting P-efficient wheat genotypes, especially under limited P supplies. The current study clearly shows that (NST 3.0) model provide useful tools for studying the role of (AMF) and root length in plant P uptake.     

Effects of nitrogen feeding for extraradical mycelium of Rhizophagus irregularis maize symbiosis incorporated with phosphorus availability

In terrestrial ecosystems, plants are frequently in symbiosis with arbuscular mycorrhizal fungi (AMF) with mineral nutrients and photosynthesis carbon exchanges in between. This research sought to identify the effects of phosphorus (P) levels on the nitrogen (N) uptake via extraradical mycelium (ERM) and the mycorrhizal growth response (MGR) of maize plants within the AMF symbiosis. Pots were separated into root compartments and hyphae compartments (HCs) with two layers of a 30‐μm mesh membrane and an air gap in between, where only hyphae could pass through, to avoid both N diffusion and root growth effects. Maize plants were inoculated with Rhizophagus irregularis with different N fertilization in HCs under two different P fertilization levels. Our results indicated that a strong increase in MGR with low‐P fertilization. The same tendency was not observed with high‐P fertilization, although both had a large increase in P concentration as a potential source of growth in shoot tissue of mycorrhizal plants. Substantial effects (10.5% more N) were observed in the case of high‐P availability for the host plants from ERM fed with N, whereas under low‐P conditions ERM may prioritize P uptake rather than N uptake. The AM fungi increase the uptake of N and P, which are most limiting in the soil with fewer forces from soil resources. In addition, there was still more P accumulated than N due to the high N for ERM with high‐P supply. Low N in HCs corresponded with a lower colonization rate in roots but with high hyphae density in HCs; this result suggest that N and P availability might change the ratio of extraradical to intraradical hyphae length.     

Defoliation effects on the arbuscular mycorrhizas of ten perennial grass genotypes in arid Patagonia,Argentina

Pappophorum vaginatum is the most abundant C₄, warm-season perennial grass in rangelands of northeastern, arid Patagonia, which is often exposed to continuous grazing. Eragrostis curvula is the only naturalized, C₄ warm-season genotype that has successfully established from seed during moist years in the study region, that is characterized by a scarce forage availability to livestock during the spring and summer. Successful introduction of perennial forage genotypes is then critical in that region. No studies have yet been conducted to determine the greater abundance of P. vaginatum compared to that of other native C₄ grass genotypes (Aristida subulata, A. spegazzinii, Sporobolus cryptandrus) in the study area. The effect of defoliation on arbuscular mycorrhizal colonization was investigated on the four native, one naturalized and five introduced, C₃ perennial grass genotypes (Leymus cinereus cvs. “Magnar” and “Trailhead”, and Achnatherum hymenoides cvs. “Paloma”, “Rimrock” and “Nezpar”) growing at the field. We hypothesized that the magnitude of mycorrhizal colonization (1) is similar on defoliated than on undefoliated plants of the native and naturalized genotypes, (2) is greater in the native and naturalized than in the introduced genotypes, and (3) is greatest in P. vaginatum than in all remaining genotypes. Plants of all ten genotypes were either exposed or not to a severe defoliation twice in the growing seasons of 2007/2008 and 2008/2009. The results showed that all studied genotypes maintained arbuscular mycorrhizal colonization levels following defoliation similar to undefoliated controls. The greatest arbuscular mycorrhizal colonization was often found on both cultivars of L. cinereus among all genotypes. The greatest arbuscular mycorrhizal colonization in P. vaginatum than in the other native genotypes at the end of the study, parameter that contributes to defoliation tolerance, could help to explain its greater abundance in rangelands of central Argentina. The higher arbuscular mycorrhizal colonization in both cultivars of L. cinereus might contribute to their successful establishment and survival in rangelands of northeastern, arid Patagonia. Genotype introduction in these rangelands is likely to affect community dynamics because of variable effects of the mycorrhizal symbiosis on the various plant genotypes.     

Solubilization of Insoluble Inorganic Phosphate by Hyphal Exudates of Arbuscular Mycorrhizal Fungi

Increased phosphate (P) uptake in plants by arbuscular mycorrhizal (AM) fungi is thought to depend mainly on the extension of external hyphae into soil. On the other hand, it is known that the hyphae of some kinds of ectomycorrhizal fungi release organic acids into soil and that they dissolve the insoluble inorganic P. This study collected hyphal exudates of AM fungi within compartmentalized pot culture and clarified their ability to solubilize insoluble inorganic P. Sterilized Andisol was packed in pots that were separated into root and hyphal compartments with a nylon net of 30 μm pore size. Seedlings of Allium cepa inoculated with AM fungi, Gigaspora margarita, or Glomus etunicatum were grown. Control pots were not inoculated. Mullite ceramic tubes were buried in the soil of each compartment and soil solution was collected. The anionic fraction of the soil solution was incubated with iron phosphate (4 mg FePO₄ in 1 mL of 0.4 acetate buffer). Solubilized P was measured. The AM colonization of plants inoculated with G. margarita and G. etunicatum was 86% and 54%, respectively. Adhesion of external hyphae was observed on the surface of the mullite ceramic tubes buried in soil of the hyphal compartment. Colonization of both fungi increased shoot P uptake and growth. Soil solution collected from the hyphal compartments of both fungi solubilized more P than did that from uninoculated plants. It is suggested that hyphal exudates can contribute to increased P uptake of colonized plants.