Inoculation of arbuscular mycorrhizal fungi can substantially reduce phosphate fertilizer application to Allium fistulosum L. and achieve marketable yield under field condition

The effects of inoculating arbuscular mycorrhizal (AM) fungi on the growth, phosphorus (P) uptake, and yield of Welsh onion (Allium fistulosum L.) were examined under the non-sterile field condition. Welsh onion was inoculated with the AM fungus, Glomus R-10, and grown in a glasshouse for 58?days. Non-inoculated plants were grown as control. Inoculated and non-inoculated seedlings were transplanted to a field with four available soil P levels (300, 600, 1,000, and 1,500?mg P₂O₅?kg^?1 soil) and grown for 109?days. AM fungus colonization, shoot P concentration, shoot dry weight, shoot length, and leaf sheath diameter were measured. Percentage AM fungus colonization of inoculated plants was 94% at transplant and ranged from 60% to 77% at harvest. Meanwhile, non-inoculated plants were colonized by indigenous AM fungi. Shoot length and leaf sheath diameter of inoculated plants were larger than those of non-inoculated plants grown in soil containing 300 and 600?mg P₂O₅?kg^?1 soil. Shoot P content of inoculated plants was higher than that of non-inoculated plants grown in soil containing 300 and 600?mg P₂O₅?kg^?1 soil. Yield (shoot dry weight) was higher for non-inoculated plants grown in soil containing 1,000 and 1,500?mg P₂O₅?kg^?1 soil than for those grown in soil containing 300 and 600?mg?P₂O₅ kg^?1 soil. Meanwhile, the yields of inoculated plants (200?g plant^?1) grown in soils containing the four P levels were not significantly different. Yield of inoculated plants grown in soil containing 300?mg P₂O₅ kg^?1 soil was similar to that of non-inoculated plants grown in soil containing 1,000?mg P₂O₅?kg^?1 soil. The cost of AM fungal inoculum for inoculated plants was US$ 2,285?ha^?1 and lower than the cost of superphosphate (US$ 5,659?ha^?1) added to soil containing 1,000?mg P₂O₅ kg^?1 soil for non-inoculated plants. These results indicate that the inoculation of AM fungi can achieve marketable yield of A. fistulosum under the field condition with reduced application of P fertilizer.     

Fertilizer Concentration Affects Growth Response and Leaf Color of Tradescantia virginiana L.

ABSTRACT

A pot experiment was conducted out to investigate the yield and pungency of spring onion (Allium fistulosum L.) as affected by inoculation with arbuscular mycorrhizal (AM) fungi and addition of nitrogen (N) and sulfur (S) fertilizers. Plants were inoculated with either Glomus mosseae or Glomus intraradices or grown as uninoculated controls. Two levels of N and S were applied to the soil in factorial combinations of 50 and 250 mg N kg^?1 soil and 0 and 60 mg S kg^?1 soil. Plants were grown in a greenhouse for 25 weeks and then harvested. Mycorrhizal colonization resulted in increased shoot dry weight, shoot-to-root ratio, shoot length, sheath diameter, and phosphorus (P) concentrations. Shoot dry-matter yield was significantly affected by added N, but not by S. Shoot dry weight increased with increasing N supply (except for non-mycorrhizal controls without additional S fertilizer). Shoot total S concentration (TSC), enzyme-produced pyruvate (EPY), and organic sulfur concentration (OSC) in plants inoculated with Glomus mosseae were significantly lower than those of non-mycorrhizal controls, while these parameters in plants inoculated with Glomus intraradices were comparable to or higher than in the controls. Neither N nor S supply affected shoot EPY or OSC, whereas shoot TSC (except in plants inoculated with Glomus mosseae) and SO₄ ^2? concentrations were usually significantly increased by S supply. In soil of high S and low P availability, mycorrhizal colonization had a profound influence on both the yield and the pungency of spring onion.     

AM真菌对田间山银花生长、矿质营养及绿原酸含量的影响

Lonicera confusa, a traditional Chinese medicine herb for treating cold, flu, acute fever, and so forth, is often grown artificially in acidic soils and suffers from phosphorus (P) deficiency. A five-year field experiment was carried out to study the colonization rate, growth, nutrition, and chlorogenic acid content of Lonicera confusa seedlings inoculated with arbuscular mycorrhizal (AM) fungi, Glomus etunicatum and Glomus intraradices. Before transplanting into a field, both AM-inoculated and uninoculated control plants were cultured in nursery beds. In the plants inoculated with the AM fungi, the colonization rate decreased linearly with time and a greater decrease was observed in the plants inoculated with G. intraradices than with G. etunicatum, while the AM colonization increased from 0% to 12.1% in the uninoculated control plants 5 years after transplanting. Plant height, crown diameter, number of new branches, and flower yield increased significantly by AM inoculation as compared to the uninoculated control. Phosphorus concentrations in leaves and flowers increased, and plant uptake of nutrients, e.g., nitrogen (N), P, and potassium (K), was also enhanced significantly by AM inoculation. The Lonicera confusa seedlings had a better response to inoculation of G. intraradices than G. etunicatum in both growth and chlorogenic acid content in flowers. In contrast, both plant P uptake and P concentrations in leaves and flowers were similar between two fungal inoculations. The positive responses of Lonicera confusa to AM inoculation in growth, nutrient uptake, flowering, and chlorogenic acid content in flowers suggested that AM inoculation in nursery beds could promote the plant growth and increase chlorogenic acid content in flowers of Lonicera confusa when grown on acidic and P-deficient soils.     

Response of Sauropus androgynus to soil phosphorus concentration and mycorrhizal colonization

Thirty three‐day‐old seedlings of nonmycorrhizal Sauropus androgynus were transplanted into pots containing a subsurface Oxisol uninoculated or inoculated with Glomus aggregation at three target soil solution phosphorus (P) concentrations. While no evidence of vesicular‐arbuscular mycorrhizal fungal (VAMF) colonization was noticed in the uninoculated soil, sauropus roots were colonized to the extent of 54%, 60% and 38% in the inoculated soil if target soil P concentrations were 0.014, 0.02 and 0.2 mg/L. VAMF colonization led to significant increases in tissue P and shoot dry matter accumulation at the first two soil P concentrations but not at the highest concentration. Root dry matter yield of mycorrhizal sauropus was greater than that of nonmycorrhizal sauropus at all soil P concentrations tested. Although mycorrhizal inoculation effects at soil P concentrations of 0.014 and 0.02 mg/L were comparable, growth of mycorrhizal plants was greater at the latter P concentration than at the former. Growth of mycorrhizal sauropus at this P concentration was also comparable to non‐mycorrhizal growth of the plant at soil P concentration of 0.2 mg/L. Based on the growth responses observed sauropus was classified as a highly mycorrhizal dependent species.     

Arbuscular mycorrhizal fungi influence tomato competition with bahiagrass

A strip-tillage production system for tomatoes (Lycopersicon esculentum Mill.) is impacted by nutrient competition from bahiagrass (Paspalum notatum Flügge). Tomato and bahiagrass differ in mycorrhizal responsiveness and our objective was to evaluate the influence of arbuscular mycorrhizal (AM) fungi on the competitive pressure of bahiagrass on growth of tomato. The first experiment evaluated the effect of bahiagrass competition, soil pasteurization, and AM fungal inoculation on tomato growth, P content, and root colonization in a low-P soil. Tomato grown alone was very responsive to mycorrhizal colonization - shoot dry mass of inoculated plants was up to 243% greater than that of noninoculated plants. Tomato grown with bahiagrass had reduced root and shoot growth across all treatments compared with tomato grown alone, but there was an increase in shoot mass following AM fungal inoculation across both pasteurized and nonpasteurized treatments resulting in a >50% increase in shoot dry mass of tomato compared to noninoculated controls. A second experiment was conducted to test bahiagrass competition, soil pasteurization, AM fungal inoculation, and P amendment on tomato growth in a moderate-P soil. With bahiagrass competition and no P addition, inoculation increased root mass by 115% and shoot mass by 133% in pasteurized soil; however, with the application of 32 mg P kg^-1 the trend was reversed and inoculated plants were smaller than noninoculated controls. We conclude that the role of mycorrhizae in plant competition for nutrients is markedly impacted by soil nutrient status and reduced P application may allow tomatoes to take advantage of their inherent responsiveness to mycorrhizae in a low to moderate soil-P environment.     

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.     

Involvement of autoregulation in the interaction between rhizobial nodulation and AM fungal colonization in soybean roots

Soybean plants autoregulate to suppress excessive nodulation. It has been revealed recently that the autoregulation of various legumes controls both nodulation and arbuscular mycorrhizal (AM) fungal colonization. We investigated the involvement of autoregulation in the interaction between rhizobial nodulation and AM fungal colonization. We used a wild-type soybean cv. Enrei and its hypernodulating mutant Kanto100, defective in the autoregulation. We included four different treatments: an uninoculated control, inoculation with rhizobium Bradyrhizobium japonicum alone, inoculation with AM fungus Gigaspora rosea alone, and dual inoculation with rhizobium and AM fungus. In both Enrei and Kanto100, AM fungal colonization enhanced the weight and N₂ fixation of nodules, suggesting that autoregulation of host plant is not involved in the stimulatory effect of AM fungal colonization on rhizobial nodulation. In plants with the AM fungus alone, the AM fungal colonization of Enrei was comparable to that of Kanto100. In plants with dual inoculation, however, this was significantly (P?<?0.05) lower than in Kanto100. To confirm the control of AM fungal colonization by the autoregulation of host plant, a reciprocal grafting experiment was performed between Enrei and Kanto100. In plants with the AM fungus alone, AM fungal colonization was comparable among Enrei (shoot)/Enrei (root), Enrei/Kanto100, Kanto100/Enrei, and Kanto100/Kanto100 grafts. In plants with dual inoculation, however, AM fungal colonization of Enrei/Enrei and Enrei/Kanto100 grafts was significantly (P?<?0.05) lower than that of Kanto100/Enrei and Kanto100/Kanto100. These results indicate that rhizobial nodulation suppresses AM fungal colonization, and the autoregulation of host plant, initiated by nodulation, is involved in this phenomenon.     

Pungency of Spring Onion as Affected by Inoculation with Arbuscular Mycorrhizal Fungi and Sulfur Supply

ABSTRACT

The influence of sulfur (S) supply and mycorrhizal colonization on the growth and pungency of spring onion (Allium fistulosum L.) seedlings grown for four months in Perlite and nutrient solution containing three levels of sulfate [0.1, 1.75, and 4 mM sulfate (SO₄ ^2?)] were investigated. Plants were inoculated with Glomus etunicatum, Glomus intraradices, or Glomus mosseae, and uninoculated controls were included. Shoot and root dry weights of mycorrhizal and control plants supplied with 4 mM SO₄ ²⁺ were higher than with 0.1 or 1.75 mM SO₄ ^2?. Enzyme produced pyruvic acid (EPY) and plant sulfur concentrations increased with increasing SO₄ ^2? supply. The EPY and plant S concentrations were usually higher in mycorrhizal plants than controls irrespective of S supply, and shoot total S concentrations and EPY were strongly correlated. Arbuscular mycorrhizal colonization appeared to make a substantial contribution to the sulfur status of spring onion, and may thus have had a strong influence on its flavor characteristics.     

Dependency of Cassia siamea on vesicular arbuscular mycorrhizal fungi

Thirty‐day‐old seedlings of Cassia siamea were transplanted into pots containing a subsurface Oxisol uninoculated or inoculated with Glomus agaregatum at two target soil solution phosphorus (P) concentrations. While no evidence of Vesicular‐arbuscular mycorrhizal fungal (VAMF) colonization was noted in the uninoculated soil, C. siamea roots were colonized to the extent of 63 and 61% at soil P concentrations of 0.02 and 0.2 mg/L, respectively. VAMF colonization led to significant increases in tissue P concentrations measured at harvest at both soil P concentrations. However, shoot dry matter yield was significantly increased only at the first soil P concentration. Shoot dry matter yield of mycorrhizal C. siamea at soil P concentration of 0.02 mg/L was comparable to mycorrhizal growth of C. siamea at soil P concentration of 0.2 mg/L but inferior to the nonmycorrhizal growth of the legume. Based on these response patterns, C. siamea was classified as a highly mycorrhizal dependent species.     

Influence of inoculation with arbuscular mycorrhizal fungi on stable isotopes of nitrogen in Phaseolus vulgaris

The interactions between Phaseolus vulgaris, Rhizobium spp. strains nodulating P. vulgaris, and arbuscular mycorrhizal (AM) fungi were assessed under greenhouse conditions in a nonsterilized Typic Haplustalf soil from Cauca, Colombia. Our results indicate a specific involvement of AM fungal species in nitrogen acquisition by the legume plants from symbiotic nitrogen fixation and from soil. A significant specific influence of inoculation with Glomus spp. on the ¹⁵N/¹⁴N ratio in plant shoots was dependent on the inoculated rhizobial strain, but AM fungal inoculation had no significant effect on shoot dry weight or nodule occupancy in the two different rhizobial strain treatments. The results imply that in low P soils the effects of an improved mycorrhizal symbiosis may include improved symbiotic N₂ fixation efficiency and/or improved soil N uptake. Received: 11 May 1996     

Influence of arbuscular mycorrhizal fungi and salinity on growth,biomass, and mineral nutrition of<Emphasis Type="Italic"> Acacia auriculiformis</Emphasis>

The effect of salinity on the efficacy of two arbuscular mycorrhizal fungi, Glomus fasciculatum and G. macrocarpum, alone and in combination was investigated on growth, development and nutrition of Acacia auriculiformis. Plants were grown under different salinity levels imposed by 0.3, 0.5 and 1.0 S m^-1 solutions of 1 M NaCl. Both mycorrhizal fungi protected the host plant against the detrimental effect of salinity. The extent of AM response on growth as well as root colonization varied with fungal species, and with the level of salinity. Maximum root colonization and spore production was observed with combined inoculation, which resulted in greater plant growth at all salinity levels. AM fungal inoculated plants showed significantly higher root and shoot weights. Greater nutrient acquisition, changes in root morphology, and electrical conductivity of soil in response to AM colonization was observed, and may be possible mechanisms to protect plants from salt stress.     

MYCORRHIZAL INFLUENCE ON FRUIT YIELD AND MINERAL CONTENT OF TOMATO GROWN UNDER SALT STRESS

Tomato (Lycopersicon esculentum Mill.) yields are known to decrease for plants grown in saline soils. This study was conducted to determine the effects of arbuscular mycorrhizal fungi (AMF) inoculation on fruit yield and mineral content of salt-tolerant and salt-sensitive tomato cultivars grown with varied levels of salt. NaCl and CaCl₂were added to soil in the irrigation water in equal molar ratios to give EC_e values of 1.4 (nonstressed) and 4.9 dS m^?1 (salt stressed). Plants were grown in a greenhouse using unsterilized, low phosphorus (P) (silty clay) soil-sand mix. Mycorrhizal root colonization occurred whether cultivars were salt stressed or nonstressed, but the extent of AMF root colonization was higher in AMF inoculated than uninoculated plants. The salt tolerant cultivar ‘Pello’ generally had higher AMF root colonization than the salt sensitive cultivar ‘Marriha’. Shoot dry matter (DM) yield, fruit fresh yield, and AMF colonization were higher for plants grown under nonstressed than for plants grown under salt stressed conditions. Shoot DM and fruit fresh yields were higher in AMF inoculated than uninoculated plants grown with or without salt stress. Pello generally had higher fruit fresh yield per plant and fruit weight than Marriha, but these differences were only significant for fruit weight in unioculated plants grown under salt stressed conditions. The enhancement in fruit fresh yield due to AMF inoculation was 26 and 23% under nonstressed and 28 and 46% under salt stressed treatments for Pello and Marriha, respectively. For both cultivars, fruit contents of P, potassium (K), zinc (Zn), copper (Cu), and iron (Fe) were higher in AMF inoculated compared with uninoculated plants grown under nonstressed and salt stressed conditions. Fruit Na concentrations were lower in AMF inoculated than uninoculated plants grown under salt stressed conditions. The enhancement in P, K, Zn, Cu, and Fe acquisition due to AMF inoculation was more pronounced in Marriha than in Pello cultivar under salt stressed conditions. The results of this study indicated that AMF inoculated plants had greater tolerance to salt stress than unioculated plants.     

Water stress and mycorrhizal isolate effects on growth and nutrient acquisition of wheat

Arbuscular mycorrhizal (AM) colonized plants often have greater tolerance to drought than nonmycorrhizal (nonAM) plants. Wheat (Triticum durum Desf.), whose roots were colonized with Glomus mosseae (Gms) and G. monosporum (Gmn), were grown in a greenhouse to determine effects of water stress (WS) on shoot and root dry matter (DM), root length (RL), and shoot phosphorus (P), zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe) concentrations and contents. Mycorrhizal colonization was higher in well‐watered (nonWS) plants colonized with both AM isolates than WS plants, and Gms had greater colonization than Gmn under both soil moisture conditions. Shoot and root DM were higher in AM than in nonAM plants irrespective of soil moisture, and Gms plants had higher shoot but not root DM than Gmn plants grown under either soil moisture condition. Total RL of AM plants was greater than nonAM plants, but was consistently lower for plants grown with WS than with nonWS. The AM plants had similar shoot P and Mn concentrations as nonAM plants, but contents were higher in AM than in nonAM plants. The AM plants had higher shoot Zn, Cu, and Fe concentrations and contents than nonAM plants. The Gms plants grown under nonWS generally had higher nutrient contents than Gmn plants, but nutrient contents were similar for both Gms and Gmn plants grown under WS. The results demonstrated a positive relationship between enhanced growth and AM root colonization for plants grown under nonWS and WS.     

Response of a wild-type and modern cowpea cultivars to arbuscular mycorrhizal inoculation in sterilized and non-sterilized soil

Cowpea is an important crop that serves as a legume and vegetable source to many smallholder farmers in sub-Saharan Africa. Soil fertility is a significant limitation to its production thus; inoculation with beneficial soil biota such as arbuscular mycorrhizal fungi (AMF) could improve its performance. However, plant–AMF interaction could vary based on crop cultivar hence affecting overall crop production. The present study aimed at determining the effect of AMF inoculation and soil sterilization on root colonization and growth of a wild-type and three modern cowpea cultivars grown by smallholder farmers in Kenya. Potted cowpea plants were inoculated with a commercial AMF inoculum comprising of Rhizophagus irregularis, Funneliformis mosseae, Glomus aggregatum and Glomus etunicatum and maintained in a greenhouse for 40 days. After harvesting, mycorrhizal colonization, nodule number and dry weight, root and shoot dry weights, nitrogen (N,) phosphorus (P) and potassium (K) content were determined. Interestingly, the modern cultivars showed significantly (p < 0.001) higher root colonization, nodulation, shoot P and N compared to the wild-type cultivar. Moreover, a strong positive correlation between AMF root colonization and shoot P (r² = 0.73, 0.90, p < 0.001), AMF root colonization and shoot N (r² = 0.78; 0.89, p < 0.001) was observed in both sterilized and non-sterilized soil, respectively. Soil sterilization affected root colonization and growth parameters with plants grown in non-sterilized soil performing better than those grown in sterilized soil. This study provides major evidence that modern cowpea cultivars are still responsive to mycorrhizal inoculation suggesting that modern breeding programs are not deleterious AMF symbiosis.     

Interactions of arbuscular-mycorrhizal fungi and Bacillus strains and their effects on plant growth,microbial rhizosphere activity (thymidine and leucine incorporation) and fungal biomass (ergosterol and chitin)

The effects of two Bacillus strains (Bacillus pumillus and B. licheniformis) on Medicago sativa plants were determined in single or dual inoculation with three arbuscular-mycorrhizal (AM) fungi and compared to P-fertilization. Shoot and root plant biomass, values of thymidine and leucine incorporation as well as ergosterol and chitin in rhizosphere soil were evaluated to estimate metabolic activity and fungal biomass, respectively, according to inoculation treatments. For most of the plant parameters determined, the effectiveness of AM fungal species was influenced by the bacterial strain associated. Dual inoculation of Bacillus spp. and AM fungi did not always significantly increase shoot biomass compared to single AM-colonized plants. The most efficient treatment in terms of dry matter production was the dual Glomus deserticola plus B. pumillus inoculation, which produced similar shoot biomass and longer roots than P-fertilization and a 715% (shoot) and 190% (root length) increase over uninoculated control. The mycorrhizas were more important for N use-efficiency than for P use-efficiency, which suggests a direct mycorrhizal effect on N nutrition not mediated by P uptake. Both chemical and biological treatments affected thymidine and leucine incorporation in the rhizosphere soil differently. Thymidine was greater in inoculated than in control rhizospheres and B. licheniformis was more effective than B. pumillus in increasing thymidine. Non-inoculated rhizospheres showed the lowest thymidine and leucine values, which shows that indigenous rhizosphere bacteria increased with introduced inocula. The highest thymidine and leucine values found in P-fertilized soils indicate that AM plants are better adapted to compete with saprophytic soil bacteria for nutrients than P-amended plants. Chitin was only increased by coinoculation of B. licheniformis and G. intraradices. B. pumillus increased ergosterol (indicative of active saprophyte fungal populations) in the rhizosphere of AM plants and particularly when colonized by G. mosseae. The different AM fungi have different effects on bacterial and/or fungal saprophytic populations and for each AM fungus, this effect was specifically stimulated or reduced by the same bacterium. This is an indication of ecological compatibilities between microorganisms. Particular Glomus–bacterium interactions (in terms of effect on plant growth responses or rhizosphere population) do not seem to be related to the percentage of AM colonization. The effect on plant growth and stimulation of rhizosphere populations, as a consequence of selected microbial groups, may be decisive for the plant establishment under limiting soil conditions.     

Impact of 12-year field treatments with organic and inorganic fertilizers on crop productivity and mycorrhizal community structure

The effect of manure and mineral fertilization on the arbuscular mycorrhizal (AM) fungal community structure of sunflower (Helianthus annuus L.) plants was studied. Soils were collected from a field experiment treated for 12 years with equivalent nitrogen (N) doses of inorganic N, dairy manure slurry, or without N fertilization. Fresh roots of tall fescue (Festuca arundinacea Schreb.) grass collected from the field plots without N fertilization and unfumigated field soils were used as native microbial inoculum sources. Sunflower plants were sown in pots containing these soils, and three different means of manipulating the microbial community were set: unfumigated soil with fresh grass roots, fumigated soil with fresh grass roots, or fumigated soil with sterilized grass roots. Assessing the implications with respect to plant productivity and mycorrhizal community structure was investigated. Twelve AM fungal OTUs were identified from root or soil samples as different taxa of Acaulospora, Claroideoglomus, Funneliformis, Rhizophagus, and uncultured Glomus, using PCR-DGGE and sequencing of an 18S rRNA gene fragment. Sunflower plants grown in manure-fertilized soils had a distinct AMF community structure from plants either fertilized with mineral N or unfertilized, with an abundance of Rhizophagus intraradices-like (B2). The results also showed that AM inoculation increased P and N contents in inorganic N-fertilized or unfertilized plants, but not in manure-fertilized plants.     

Effects of Arbuscular Mycorrhizal Fungi and Ammonium: Nitrate Ratios on Growth and Pungency of Onion Seedlings

ABSTRACT

A pot experiment was conducted to study the growth and pungency of Allium cepa L. grown in Perlite as affected by colonization by the arbuscular mycorrhizal (AM) fungi Glomus versiforme and Glomus intraradices BEG141 and by ammonium:nitrate (NH₄ ⁺:NO₃ ^?) ratios of 3:1, 1:1, and 1:3 in 4 mM solutions. Plants were harvested when bulb formation commenced. In general, mycorrhizal colonization resulted in increased shoot dry weight, shoot length, sheath diameter, root nitrogen (N) and phosphorus (P) content (except with G. intraradices and a NH₄ ⁺:NO₃ ^? ratio of 1:3), shoot N and P concentrations (except with G. versiforme and a NH₄ ⁺:NO₃= ratio of 3:1) and content. Plants inoculated with G. versiforme had higher growth parameters and N and P content than those with G. intraradices, whereas N and P concentrations showed the opposite trends. Growth parameters and N and P content of non-mycorrhizal plants were highest at a NH₄ ⁺:NO₃= ratio of 1:3, while those of plants inoculated with G. versiforme or G. intraradices were highest at a ratio of NH₄ ⁺:NO₃ ^? 3:1 or 1:1. Neither mycorrhizal colonization nor proportion of inorganic N species significantly affected bulb enzyme-produced pyruvate or total or organic sulfur (S) concentrations in plant shoots. Colonization by AM fungi made a substantial contribution to onion growth and may not have been directly related to bulb pungency at early stages of plant growth. However, the influence of AM fungi on plant N and P metabolism may have implications for onion flavor at later stages of plant growth.     

Mycorrhizal dependency of two hawaiian endemic tree species: Koa and mamane 1

Vesicular‐arbuscular mycorrhizal (VAM) fungi have been proposed as a low‐input solution to the problem of inadequate phosphorus (P) levels in many tropical and subtropical soils. To determine the mycorrhizal dependency of two Hawaiian endemic tree species, mamane (Sophora chrysophylla Seem.) and koa (Acacia koa Gray), seedlings were grown in the greenhouse with and without the VAM fungus, Glomus aggregatum Schenck and Smith emend Koske, at three levels of soil solution P (0,0.02, and 0.20 mg P/L) in a volcanic ash soil. Inoculation significantly increased colonization of roots by the VAM fungus in both mamane and koa seedlings. At 0.02 mg P/L, mamane inoculated with the VAM fungus had significantly greater subleaflet P concentrations at 48 days after planting (DAP), and significantly greater leaf areas, shoot dry weights, and root lengths at harvest compared to uninoculated plants. At 0 mg P/L, koa grown in association with the VAM fungus had significantly greater subleaflet P concentrations at 41 DAP, and significantly greater leaf areas, and dry weights of leaves, stems, and roots at harvest. Mamane was highly dependent on the VAM association for maximum growth, while koa was moderately dependent on the VAM association. These results demonstrate that P uptake and early growth of mamane and koa can be increased significantly at low soil P levels by inoculating seedlings with an effective VAM fungus. Future research needs to demonstrate continuing positive growth benefits of VAM fungal inoculation after transplanting from the nursery to field conditions.     

Enhancement of growth in mangrove plant (Ceriops tagal) by Rhizophagus clarus

The present study was conducted to investigate the growth response of Ceriops tagal Perr.) C.B. Robinson a mangrove species belonging to the family Rhizophoraceae. Three dominant native arbuscular mycorrhizal (AM) fungal species viz., Rhizophagus clarus, R. intraradices, and Acaulospora laevis were selected. The results revealed that the Mycorrhizal Plant Responsiveness (MGR) was greater in AM inoculated plants compared to control plants. Among AM fungal treatments, plants inoculated with R. clarus recorded significant increase in growth responses compared to remaining AM treatments. The study suggests that R. clarus was the most efficient AM species exhibiting greater influence on growth and biomass. Differences in growth parameters between AM inoculated treatments and control are reasonably linked to colonization levels. The result of the present study indicates that potential native AM fungal species can be use in mangrove reforestation programs as bio-inoculum.     

Inoculation with arbuscular mycorrhizal fungus Acaulospora mellea decreases Cu phytoextraction by maize from Cu-contaminated soil

A pot culture experiment was carried out to study the growth of and Cu uptake by maize (Zea mays) inoculated with or without arbuscular mycorrhizal (AM) fungus Acaulospora mellea in sterilized soil with different Cu amounts added (0, 100, 200, 400, 800 mg kg⁻¹). Root colonization rates were significantly lower with the addition of 400 and 800 mg kg⁻¹ Cu. AM inoculation increased shoot dry weights at 200 and 400 mg kg⁻¹ Cu added but showed no effects at other levels, while increased root dry weights at all Cu addition levels except 800 mg kg⁻¹. Compared with the nonmycorrhizal plants, shoot Cu concentrations in mycorrhizal plants were higher when no Cu was added but lower at other levels, while root Cu concentrations were lower at 400 and 800 mg kg⁻¹ Cu added but not affected at other levels. Thus, shoot Cu uptake in mycorrhizal plants increased with no Cu added but decreased at other levels, while mycorrhizal effects on root Cu uptake varied. Compared with nonmycorrhizal controls, Cu uptake efficiency and phytoextraction efficiency in mycorrhizal plants were higher when no Cu was added but lower at other levels, and Cu translocation efficiency was lower at all Cu addition levels. AM inoculation improved shoot and root P nutrition at all Cu addition levels. Soil pH was higher in mycorrhizal treatment than in the control when 200 mg kg⁻¹ or more Cu was added. These results indicate that A. mellea ZZ may be not suitable for Cu phytoextraction by maize, but shows a potential role in phytostabilization of soil moderately polluted by Cu.