Occurrence of nitrogen-fixing Azospirillum in vesicular-arbuscular mycorrhizal fungi

Nitrogenase activity measured by acetylene reduction, was detected when surface-sterilized spores of vesicular-arbuscular (VA) mycorrhizal fungi (Glomus fasciculatum, G. intraradices, G. scientillans, G. mosseae, Gigaspora gilmorei andEndogone dusii) were inoculated into nitrogen-free liquid medium containing malic acid and incubated under microaerophilic conditions (99% N₂+1% O₂) at 30°C.Azospirillum species were isolated from the nitrogenase-active cultures.     

大豆毛状根-VA菌根真菌双重培养体系的建立

以大豆毛状根为宿主,接种VA菌根真菌珠状巨孢囊霉（Gigaspora margarita）,经过3.5个月的双重培养,观察到VA菌根真菌珠状巨孢囊霉对大豆毛状根的侵染,辅助细胞形成,并获得VA菌根真菌成熟孢子,在无菌条件下建立了大豆毛状根-VA菌根真菌双重培养体系,为研究菌根真菌侵染大豆根部形成共生体系及相关分子机制提供了一种有效的研究方法。     

The effect of vesicular arbuscular mycorrhizal associations on growth of cereals

The growth of wheat seedlings which were already mycorrhizal when transplanted to a field deficient in phosphorus was improved compared with non-mycorrhizal controls, and grain yield was increased three-fold by the fungus, indicating that Endogone stimulated growth and increased yield. Differences between mycorrhizal and non-mycorrhizal wheat were eliminated by the application of phosphate fertilizer, indicating that the fungus does not enhance wheat growth in soils containing enough available phosphate. It is probable that the mycorrhizal effect is primarily to improve the supply of phosphate. There were clear relationships between spore number in the soil and mycorrhizal development and between the extent of root infection and increased growth. The extent of root infection was greatest in mycorrhizal plants in soil not supplemented with phosphate and it decreased in inoculated plants in the plot supplemented with superphosphate. The non-centrospermous and non-zygophyllaceous weeds growing on the experimental field had typical vesicular arbuscular infection and indigenous Endogone spores in their rhizospheres. The centrospermous plants were non-mycorrhizal and had no Endogone spores in their rhizospheres.     

Enhancement of nitrogen fixation in lentil,faba bean,and soybean by dual inoculation with Rhizobia and mycorrhizae

The combined effect of Vesicular Arbuscular Mycorrhizae (VAM) and Rhizobium on the cold season legumes, lentil and faba bean, as well as on summer legume, soybean, were studied in soils with low indeginous VA mycorrhizal spores. Inoculation of the plant with VA mycorrhizal fungi increased the level of mycorrhizal root infection of lentil, faba bean and soybean. The inoculation with Rhizobium had no significant effect on VA mycorrhizal infection percent, but VA mycorrhizal inoculation increased nodulation of the three legumes. The inoculation with Rhizobium alone significantly increased plant dry weight and N content of lentil and faba bean as well as seed yield of soybean. VA mycorrhizal inoculation also significantly increased plant dry weight and phosphorus content of the plants as did fertilization with superphosphate. Rock phosphate fertilization, however, had no significant effect on plant growth or phosphorus uptake. The addition of rock phosphate in combination with VA mycorrhizal inoculation significantly increased plant dry weight and P uptake of the plants. The dual inoculation with both rhizobia and mycorrhizae induced more significant increases in plant dry weight, N and P content of lentil and faba bean as well as seed yield of soybean than inoculation with either VA mycorrhizae or Rhizobium alone.     

Disturbance of forest by trampling: Effects on mycorrhizal roots of seedlings and mature trees of Fagus sylvatica

The effects of disturbance by recreational activities (trampling) on changes in soil organic matter (SOM) and on mycorrhizal roots of seedlings and mature trees were studied in four stands of a beech (Fagus sylvatica L.) forest near Basel, Switzerland. At each site, comparable disturbed and undisturbed plots were selected. Disturbance reduced ground cover vegetation and leaf litter. Beech seedlings had lower biomass after disturbance. Ergosterol concentration in seedling roots, an indicator of mycorrhizal fungi, was lower in two of the four disturbed plots compared to undisturbed plots; these two disturbed sites had especially low litter levels. Based on ergosterol measurements, mycorrhizas of mature trees did not appear to be negatively affected by trampling. Total fine roots and SOM were higher in the disturbed than in the undisturbed plots at three sites. At the fourth site, fine roots and SOM in the disturbed areas were lower than in the undisturbed areas most probably due to nutrient input following picnic activities. Principal component analysis revealed a close correlation between SOM and fine roots of mature trees as well as litter and seedling biomass. Trampling due to recreational activities caused considerable damage to the vegetation layer and in particular to the beech seedlings and their mycorrhizal fine roots, whereas, roots of mature trees were apparently resilient to trampling.     

The influence of season and stage of development of plant on Endogone mycorrhiza of field-grown wheat.

A quantitative and qualitative survey of the indigenous Endogone population in wheat field soil and vesicular-arbuscular mycorrhiza in wheat roots as influenced by season and by the stage of development of the wheat plant was made. The number of Endogone spores in wheat field soil remained relatively unchanged in winter until January during the period of maximum root growth. The extent of formation of arbuscules was influenced by the stage of development of the wheat plants.     

A new system using Solanum tuberosum for the co-cultivation of Glomus intraradices and its potential for mass producing spores of arbuscular mycorrhizal fungi

Freshly harvested potato tubers, Solanum tuberosum var ‘Pukhraj’, were inoculated for transformation with Agrobacterium rhizogenes strain Ri1600. Hairy roots were formed after 8 days of co-cultivation and the transformation efficiency was 40 %. The transformants were transferred from Murashige and Skoog medium (MS) to Modified White’s medium (MW) and finally on a hormone-free minimal medium (M). The putative transformants were confirmed using rolA and rolB gene specific primers for the polymerase chain reaction (PCR) analysis. The root inducing (Ri) T-DNA transformed potato roots were co-cultured with Glomus intraradices (CMCCROC7) to obtain arbuscular mycorrhizal root organ cultures (AM-ROC dual cultures), which were used for studying the symbiosis with Glomus intraradices and the potential for spore production in vitro. Sporulation was comparable with the existing in vitro carrot-dual culture system. Around 60,250 spores/jar could be harvested with around 38,314 extraradical spores/jar and around 21,936 intraradical spores/jar. The new method using potato is certainly promising for the mass production of mycorrhizal biofertilizers. The viability of the spores when tested on potato roots was nearly 100 % and more than half of the roots were colonized 12 weeks after inoculation.     

Effect of Compost and Manure Soil Amendments on Nematodes and on Yields of Potato and Barley: A 7-Year Study

A 7-year study located in Prince Edward Island, Canada, examined the influence of compost and manure on crop yield and nematode populations. The compost used in this study consisted of cull waste potatoes, sawdust, and beef manure in a 3:3:1 ratio, respectively. No plant-parasitic nematodes were detected in samples collected from windrow compost piles at 5- and 30-cm depths prior to application on field plots. Low population densities of bacterial-feeding nematodes were recovered from compost windrows at the 5-cm depth. Field plots of potato (Solanum tuberosum cv. Kennebec) received compost applied at 16 metric tonnes per hectare, or beef manure applied at 12 metric tonnes per hectare. An adjacent trial with barley (Hordeum vulgare cv. Mic Mac) received only the compost treatment. In both trials the experimental design was a complete randomized block with four replicates. Data averaged over seven growing seasons indicated that population levels of root-lesion nematodes (primarily Pratylenchus penetrans) were higher in root-zone soil in potato plots treated with either compost or manure compared to the untreated control plots. The soil amendments did not affect root-knot nematode (Meloidogyne hapla) population densities in the potato plots, but clover-cyst nematodes (Heterodera trifolii) were more numerous in the root-zone soils of barley treated with compost compared to the untreated plots. Numbers of bacterial-feeding nematodes (primarily Diplogaster lheritieri) were greater in soil in potato plots treated with manure and in soil around barley roots than in untreated plots. Total yields of potato tubers averaged over seven growing seasons increased by 27% in the plots treated with either compost or manure. Grain yields of barley also were increased by 12% when compost was applied. These results indicated that organic amendments increased crop yields, but the impacts on different nematode species varied and usually increased soil population levels.     

Vesicular-arbuscular mycorrhizas and soil salinity

This review discusses the growth and activity of vesicular-arbuscular (VA) mycorrhizal fungi in saline conditions. The review includes examination of the effects of high concentrations of salts on the occurrence of VA mycorrhizal fungi in field soils, and on spore germination, growth of hyphae, establishment of the symbiosis and production of spores in controlled conditions. Information on the growth and reproduction of VA mycorrhizal fungi under saline conditions is scarce and is often circumstantial. There is clear evidence that germination of spores and subsequent hyphal growth of some VA mycorrhizal fungi are reduced by increasing concentration of salts. However, in plant growth experiments, experimental designs and methodologies have generally not allowed the direct effects of salinity on fungal growth to be separated from plant-mediated effects. There is a need for controlled studies to investigate the responses of VA mycorrhizal fungi to soil salinity. Research is required which distinguishes between effects on different phases of the fungus lifecycle and which includes in its design the ability to separate direct effects from plant-mediated influences on fungal growth and reproduction.     

Influence of vesicular-arbuscular mycorrhiza and straw mulch on growth of barley

Summary The effects of vesicular-arbuscular mycorrhiza (VAM) and of mulching on growth of barley were investigated in a factorial experiment. Plants were grown in cylinders buried in a field in soil with moderate amounts of available phosphate. VAM infection, dry weight and P uptake were determined at harvest after 10 and 161/2 weeks growth.VAM infection was reduced in the upper soil layer by straw mulch, possibly through a reduction in temperature. By the second harvest VAM increased growth by 56% in the non-mulched plots through increased P uptake but VAM did not increase growth in the mulched plots. Mulch increased growth by 85% in the non-mycorrhizal plots, and 28% in the mycorrhizal plots.     

四种蕨类植物根际土壤中VA菌根真菌孢子种群组成和季相变化

对４ 种移栽到温室中的蕨类植物根际土壤中的ＶＡ 菌根真菌孢子种群组成和季相变化进行了研究, 结果发现, ＶＡ菌根真菌孢子的产生具有明显的宿主依赖性和季相变化。在相同气候条件下, 不同植物根际土壤中的ＶＡ菌根真菌种群组成不同; 同种ＶＡ 菌根真菌在不同宿主植物根际土壤中, 孢子的丰富度有很大的差异。本文对影响ＶＡ菌根真菌孢子种群组成和季相变化的因素进行了讨论。     

Phosphorus Distribution in Red Pine Roots and the Ectomycorrhizal Fungus Hebeloma arenosa

Red pines (Pinus resinosa Ait.) were grown in a pasteurized sandy loam either unamended with phosphate or fertilized with one of two levels of phosphate (34 or 136 mg/kg) as superphosphate, and with and without addition of Hebeloma arenosa inoculum. Shoot and total dry weights of mycorrhizal seedlings grown in soil unamended with P were greater than those for nonmycorrhizal seedlings grown in the same soil, but less than the dry weights of seedlings grown in soil amended with middle to high levels of P. Mycorrhizal infection was inhibited at the highest level of P amendment. ³¹P nuclear magnetic resonance spectra of intact mycorrhizal roots showed the presence of two dominant peaks, orthophosphate (Pi) and polyphosphate (polyP). The polyP peak was absent in spectra of nonmycorrhizal roots. The ratio for areas under the two peaks, Pi/polyP, was 1.8 for mycorrhizal roots grown in both unamended soil and soil that had received middle levels of superphosphate. Apparently, the fungus strongly mediates the supply of phosphate to the tree through the production of polyP, even at growth-limiting levels of soil P, and regulates compartmentalization of P in the mycorrhizal roots.     

Response of cowpea (Vigna unguiculata) to inoculation with VA-mycorrhizal fungi and to rock phosphate fertilization in some unsterilized Nigerian soils

Summary The effects on cowpea of inoculation with vesicular-arbuscular (VA) mycorrhizal fungi and rock phosphate (RP) fertilization were studied in pots using Alagba and Araromi series soils and in the field on Alagba, Apomu and Egbeda series soils. Inoculation of the plants with VA-mycorrhizal fungi caused very rapid infection of the roots. A higher per cent mycorrhizal infection was maintained during subsequent plant growth in the field. RP application reduced the degree of infection without affecting plant growth in the field and in pot experiments. Nodulation, nitrogen fixation and utilization of RP were increased by inoculation with mycorrhizal fungi in the pot experiments but not in the field experiments. In the pot experiments, inoculated plants supplied with RP flowered earlier, and took up more phosphorus than either inoculated plants without RP or uninoculated plants. The largest response to inoculation in terms of shoot dry matter, nodule yield and nitrogen content of shoots was obtained in Alagba soil under both pot and field conditions.IITA Journal Series Paper No. 136.     

菌根真菌在红壤中对柑桔吸收磷肥的研究

接种一种球囊霉 Glomus sp.编号 CC-1于红壤中,使酸桔和枳实生苗的根系感染形成泡囊丛枝内生菌根。应用放射性同位素~(32)P 标记的可溶性磷肥和难溶性磷肥来研究菌根真菌对柑桔吸收磷肥的作用。放射性宏观自显影和显微自显影表明菌根真菌加强了柑桔对两类磷肥的吸收。放射性测量和化学分析证明有菌根柑桔实生苗的地上部含磷量以及从红壤中和从肥料中吸收的磷量比无菌根的增多,有菌根实生苗的生长反应也较好。     

Fructifications of an Endogone Species causing Endotrophic Mycorrhiza in Fruit Plants

The fructifications of a hitherto undescribed Endogone sp. havebeen found in organic connexion with mycorrhizal strawberryroots grown in pots in a greenhouse. By inoculating sterilizedsoil with these fructifications and with spores excised fromthem it has been possible to produce typical vesicular-arbuscularinfections in strawberry, apple, and a number of other plants.These inoculation experiments constitute the first record ofthe establishment of endotrophic mycorrhizal infection in plantsraised under aseptic conditions.     

The response of ectomycorrhizal fungal inoculum to long-term increases in nitrogen supply

The inoculum of ectomycorrhizal (EM) fungi was examined in a 16 y long nitrogen fertilization experiment maintained in a temperate oak savanna. To measure EM fungal inoculum, bur oak seedlings were grown in three types of bioassays: (i) intact soil cores that measure inoculum such as spores, mycelia and mycorrhizal roots; (ii) resistant propagule bioassays that measure inoculum types resistant to soil drying; and (iii) previously mycorrhizal root bioassays that measure the ability of EM fungi to colonize new roots from mycorrhizal roots. Colonization of bur oak seedlings was characterized by morphotyping and where necessary by restriction analysis and internal transcribed spacer (ITS) sequencing. Fourteen morphotypes were found in intact soil core bioassays with species of Cortinarius, Cenococcum and Russula abundant. Five morphotypes were found in resistant propagule bioassays with Cenococcum, a thelephoroid morphotype and a Wilcoxina-like ascomycete abundant and frequent. In intact soil core bioassays total percent root colonization and number of morphotypes were not affected by N supply in 2000 and 2001. However the composition of EM fungi colonizing oak seedling roots was different with increased N supply such that Russula spp. (primarily Russula aff. amoenolens) were most abundant at the highest level of N supply. Dominant Russula spp. did not colonize any roots in resistant propagule bioassays but did colonize oak seedling roots from previously mycorrhizal roots. Results suggest that in this savanna N supply can influence the kinds of inoculum propagules present and thereby might affect the dynamics of ectomycorrhizal communities by differentially influencing reproductive and colonization strategies.     

Preinoculation with VA mycorrhiza improves growth and yield of chilli transplanted in the field and saves phosphatic fertilizer

Summary Nursery beds were inoculated with four different VA mycorrhizal fungi,Glomus fasciculatus and three local isolates I₄, I₆ and I₁₄, and mycorrhizal seedlings were transplanted to field plots with two levels of phosphatic fertilizer. Of the fungi studied, isolate I₄ increased significantly growth, P and Zn nutrition, flowering, yield of chilli plants and also the ascorbic acid content of green chillies. Yield of I₄ inoculated plants given half the recommended level of P was slightly more than the uninoculated plants given the full level of phosphatic fertilizer. This suggests the possibility of extending the simple technology of inoculating nursery beds with mycorrhiza to farmers in order to improve plant growth and save phosphatic fertilizer.     

混栽杨树-刺槐间磷素养分转移途径的研究

应用^32P同位素示踪法,人工接种VA菌根菌(Glomus mosseae),对种植在根箱中的杨树(Populus euramericana cv.‘I-214')和刺槐(Robinia pseudoacia)苗木进行了树种间P素养分转移途径的研究．结果表明,5室根箱中,接种VA菌根菌的杨树一例,菌根侵染率为34％,根箱隔网另一侧的刺槐根系侵染率为26％,而对照的杨树和刺槐根系侵染率均为零．在杨树一例施放射性同位累^32P,施用后第14—27天,刺槐一例的放射性同位素值,处理显著高于对照(P＜0．05)、在根箱中的杨树和刺槐根系间观察到菌丝连接,表明人工接种VA菌根菌能在杨树和刺槐根系间产生菌丝桥,菌丝桥可以在杨树和刺槐根系间传递P素．养分转移定量分析表明,根系接触和根系分泌物是树种间P素转移的主要途径,其转移P素量占转移总量的62％;菌根菌等微生物活动及其与根系接触和根系分泌物两种途径的交互作用占38％;菌丝桥通过隔网发挥的作用仅表现为一种趋势．     

Reducing airborne ectomycorrhizal fungi and growing non-mycorrhizal loblolly pine (Pinus taeda L.) seedlings in a greenhouse

Atmospheric spores of ectomycorrhizal (ECM) fungi are a potential source of contamination when mycorrhizal studies are performed in the greenhouse, and techniques for minimizing such contamination have rarely been tested. We grew loblolly pine (Pinus taeda L.) from seed in a greenhouse and inside a high-efficiency particulate air-filtered chamber (HFC) constructed within the same greenhouse. Seedlings were germinated in seven different sand- or soil-based and artificially based growth media. Seedlings grown in the HFC had fewer mycorrhizal short roots than those grown in the open greenhouse atmosphere. Furthermore, the proportion of seedlings from the HFC that were completely non-mycorrhizal was higher than that of seedlings from the greenhouse atmosphere. Seedlings grown in sterilized, artificially based growth media (>50% peat moss, vermiculite, and/or perlite by volume) had fewer mycorrhizal short roots than those grown in sand- or soil-based media. The HFC described here can minimize undesirable ECM colonization of host seedlings in greenhouse bioassays. In addition, the number of non-mycorrhizal seedlings can be maximized when the HFC is used in combination with artificially based growth media.     

Terrestrial vertebrates promote arbuscular mycorrhizal fungal diversity and inoculum potential in a rain forest soil

We examined whether terrestrial vertebrates affected the arbuscular mycorrhizal fungal spore communities and mycorrhizal inoculum potential (MIP) of a tropical rain forest soil by comparing plots where terrestrial vertebrates had been excluded for 3 years to adjacent control plots. We extracted spores from soil using sucrose density gradient centrifugation and assayed MIP by growing seedlings of maize ( Zea mays ) and a rain forest tree ( Flindersia brayleana ) in intact soil cores from exclosure and control plots. Control plots had significantly higher spore abundance, species richness and diversity than exclosures. Spore community composition also differed significantly between exclosure and control plots. Seedlings of both plant species grown in control cores had significantly higher arbuscular-mycorrhizal colonization than those grown in exclosure cores. This study suggests that loss of vertebrates could alter rates of mycorrhizal colonization with consequences for community and ecosystem properties.