Growth Responses of Three European Weeds on Different AMF Species during Early Development.

Arbuscular mycorrhizal fungi (AMF) have multiple functions in agroecosystems and affect many processes below- and aboveground, including plant productivity. Mycorrhizal symbiosis is not necessarily beneficial for the host plant and the growth response can be not only positive but also neutral or negative. Among other factors, the responsiveness of plants to AMF depends on the plant-fungus combination. To find out whether the AMF species or isolate is a decisive factor for growth responses of weeds, 44 AMF isolates were tested in a pot experiment for their effects on three agricultural weeds: Echinochloa crus-galli, Solanum nigrum and Papaver rhoeas. The 44 isolates cover 18 AMF species from 13 genera and all 5 orders of the Glomeromycota. The aboveground biomass of the weeds was determined after different times of growth of each weed. In most cases, the effects of AMF isolates on weed growth were negative or neutral. We conclude that some weed species do not benefit from AMF in terms of growth. AMF species can even cause negative growth responses, an effect that may be of practical interest for organic farming where the aim is to obtain a high diversity and concentration of native AMF for the benefit of the cultivated crops without increasing the labor for mechanical weeding.

Ancient lineages of arbuscular mycorrhizal fungi provide little plant benefit.

Almost all land plants form symbiotic associations with arbuscular mycorrhizal fungi (AMF). Individual plants usually are colonized by a wide range of phylogenetically diverse AMF species. The impact that different AMF taxa have on plant growth is only partly understood. We screened 44 AMF isolates for their effect on growth promotion and nutrient uptake of leek plants (Allium porrum), including isolates that have not been tested previously. In particular, we aimed to test weather AMF lineages with an ancient evolutionary age differ from relatively recent lineages in their effects on leek plants. The AMF isolates that were tested covered 18 species from all five AMF orders, eight families, and 13 genera. The experiment was conducted in a greenhouse. A soil-sand mixture was used as substrate for the leek plants. Plant growth response to inoculation with AMF varied from - 19 to 232% and depended on isolate, species, and family identity. Species from the ancient families Archaeosporaceae and Paraglomeraceae tended to be less beneficial, in terms of stimulation plant growth and nutrient uptake, than species of Glomeraceae, Entrophosporaceae, and Diversisporaceae, which are considered phylogenetically more recent than those ancient families. Root colonization levels also depended on AMF family. This study indicates that plant benefit in the symbiosis between plants and AMF is linked to fungal identity and phylogeny and it shows that there are large differences in effectiveness of different AMF.

[Filamentous and phosphate solubilizing fungi relationships with some edaphic parameters and coffee plantations management]. / Relaciones entre los hongos filamentosos y solubilizadores de fosfatos con algunas variables edáficas y el manejo de cafetales.

Soil properties and the environment have multiple outcomes on fungal communities. Although, the interaction effects between management intensity, pH, available phosphorus, organic carbon, soil texture and different fractions of water stable macro-aggregates on the communities of microscopic filamentous fungi (MFF), iron phosphate solubilizing fungi (PSF-Fe), and iron and calcium phosphate solubilizing fungi (PSF-(Fe+Ca)), have been previously evaluated in field conditions, this has never been performed in terms of their combined effects, neither with phosphate solubilizing fungi. To assess this, we collected 40 composite soil samples from eight Mexican and Colombian coffee plantations, with different management intensities and physico-chemical edaphic parameters, during 2008-2009. We isolated different communities of MFF, PSF-Fe and PSF-(Fe+Ca), by wet sieving and soil particles culture in Potato-Dextrose-Agar from soil samples, and we classified isolates in terms of their phosphate solubilizing ability. Following the principal component analysis results, we decided to analyze fungal communities and abiotic factors interactions for each country separately. Structural Equation Models revealed that organic carbon was positively associated to MFF richness and number of isolates (lambda>0.58), but its relationship with PSF-Fe and PSF-(Fe+Ca) were variable; while the available phosphorus, pH and water stable macro-aggregate fractions did not show a clear pattern. Management intensity was negatively related to PSF-Fe (lambda < or = -0.21) morphotype richness and the number of isolates in Colombian coffee plantations. We found that the relationships of clay and organic carbon content, and available phosphorus and soil pH, with the species richness and number of isolates of MFF, PSF-Fe and PSF-(Fe+Ca) were highly variable; this made impossible to generalize the responses between saprotrophic fungal groups and geographic zones. The management intensity was not related to species richness and number of isolates of MFF in any coffee areas, while for PSF the relationship could not be defined. The different water stable macro-aggregates fractions did not show a defined pattern in relation to the species richness and the number of isolates of saprophytic and phosphate solubilizing fungi (PSF). This study highlights the need to take into account edaphic and geographic context in order to reach a better understanding of the intensity management effects on MFF and PSF function in agroecosystems.

Relaciones entre los hongos filamentosos y solubilizadores de fosfatos con algunas variables edáficas y el manejo de cafetales / Filamentous and phosphate solubilizing fungi relationships with some edaphic parameters and coffee plantations management

Soil properties and the environment have multiple outcomes on fungal communities. Although, the interaction effects between management intensity, pH, available phosphorus, organic carbon, soil texture and different fractions of water stable macro-aggregates on the communities of microscopic filamentous fungi (MFF), iron phosphate solubilizing fungi (PSF-Fe), and iron and calcium phosphate solubilizing fungi (PSF-(Fe+Ca)), have been previously evaluated in field conditions, this has never been performed in terms of their combined effects, neither with phosphate solubilizing fungi. To assess this, we collected 40 composite soil samples from eight Mexican and Colombian coffee plantations, with different management intensities and physico-chemical edaphic parameters, during 2008-2009. We isolated different communities of MFF, PSFFe and PSF-(Fe+Ca), by wet sieving and soil particles culture in Potato-Dextrose-Agar from soil samples, and we classified isolates in terms of their phosphate solubilizing ability. Following the principal component analysis results, we decided to analyze fungal communities and abiotic factors interactions for each country separately. Structural Equation Models revealed that organic carbon was positively associated to MFF richness and number of isolates (λ>0.58), but its relationship with PSF-Fe and PSF-(Fe+Ca) were variable; while the available phosphorus, pH and water stable macro-aggregate fractions did not show a clear pattern. Management intensity was negatively related to PSF-Fe (λ≤-0.21) morphotype richness and the number of isolates in Colombian coffee plantations. We found that the relationships of clay and organic carbon content, and available phosphorus and soil pH, with the species richness and number of isolates of MFF, PSF-Fe and PSF-(Fe+Ca) were highly variable; this made impossible to generalize the responses between saprotrophic fungal groups and geographic zones. The management intensity was not related to species richness and number of isolates of MFF in any coffee areas, while for PSF the relationship could not be defined. The different water stable macro-aggregates fractions did not show a defined pattern in relation to the species richness and the number of isolates of saprophytic and phosphate solubilizing fungi (PSF). This study highlights the need to take into account edaphic and geographic context in order to reach a better understanding of the intensity management effects on MFF and PSF function in agroecosystems.

El suelo y sus propiedades tienen múltiples relaciones con las comunidades fúngicas. El efecto conjunto de la intensidad de manejo y las variables edáficas, incluida la estabilidad de agregados sobre las comunidades de hongos microscópicos filamentosos (HMF), solubilizadores de fosfato de hierro (HSP-Fe) y solubilizadores tanto de fosfato de hierro como de calcio (HSP-(Fe+Ca)) no han sido evaluadas en campo. A partir de 40 muestras edáficas de ocho plantaciones de café de Colombia y México, con diferentes intensidades de manejo (IMPC) y con diferencias en sus variables edáficas, se aislaron y evaluaron las comunidades de HMF, HSP-Fe y HSP-(Fe+Ca) durante 2008-2009. Empleando modelos basados en ecuaciones estructurales se encontró que el carbono orgánico se relacionó positivamente con la riqueza y abundancia de HMF (λ>0.58) y fue variable en su relación con HSP-Fe y HSP-(Fe+Ca). Las relaciones del fósforo disponible, pH y las fracciones de macro-agregados fueron altamente variables. El IMPC se relacionó negativamente con HSP-Fe (λ≤-0.21) en cafetales colombianos. Se discuten las interacciones para cada conjunto de variables (químicas, estabilidad de macro-agregados y de manejo de plantación) y se explican las relaciones resultantes. Las relaciones de cada variable son inseparables del contexto edáfico y geográfico, los cuales imprimen marcadas diferencias.

Advances in Glomeromycota taxonomy and classification.

Concomitant morphological and molecular analyses have led to major breakthroughs in the taxonomic organization of the phylum Glomeromycota. Fungi in this phylum are known to form arbuscular mycorrhiza, and so far three classes, five orders, 14 families and 29 genera have been described. Sensulato, spore formation in 10 of the arbuscular mycorrhiza-forming genera is exclusively glomoid, one is gigasporoid, seven are scutellosporoid, four are entrophosporoid, two are acaulosporoid, and one is pacisporoid. Spore bimorphism is found in three genera, and one genus is associated with cyanobacteria. Here we present the current classification developed in several recent publications and provide a summary to facilitate the identification of taxa from genus to class level.

Biodiversity of arbuscular mycorrhizal fungi in roots and soils of two salt marshes.

The occurrence of arbuscular mycorrhizal fungi (AMF) was assessed by both morphological and molecular criteria in two salt marshes: (i) a NaCl site of the island Terschelling, Atlantic Coast, the Netherlands and (ii) a K(2)CO(3) marsh at Schreyahn, Northern Germany. The overall biodiversity of AMF, based on sequence analysis, was comparably low in roots at both sites. However, the morphological spore analyses from soil samples of both sites exhibited a higher AMF biodiversity. Glomus geosporum was the only fungus of the Glomerales that was detected both as spores in soil samples and in roots of the AMF-colonized salt plants Aster tripolium and Puccinellia sp. at both saline sites and on all sampling dates (one exception). In roots, sequences of Glomus intraradices prevailed, but this fungus could not be identified unambiguously from DNA of soil spores. Likewise, Glomus sp. uncultured, only deposited as sequence in the database, was widely detected by DNA sequencing in root samples. All attempts to obtain the corresponding sequences from spores isolated from soil samples failed consistently. A small sized Archaeospora sp. was detected, either/or by morphological and molecular analyses, in roots or soil spores, in dead AMF spores or orobatid mites. The study noted inconsistencies between morphological characterization and identification by DNA sequencing of the 5.8S rDNA-ITS2 region or part of the 18S rDNA gene. The distribution of AMF unlikely followed the salt gradient at both sites, in contrast to the zone formation of plant species. Zygotes of the alga Vaucheria erythrospora (Xanthophyceae) were retrieved and should not be misidentified with AMF spores.

Acaulospora alpina, a new arbuscular mycorrhizal fungal species characteristic for high mountainous and alpine regions of the Swiss Alps.

Acaulospora alpina sp. nov. forms small (65-85 microm diam), dark yellow to orange-brown spores laterally on the neck of hyaline to subhyaline sporiferous saccules. The spores have a three-layered outer spore wall, a bi-layered middle wall and a three-layered inner wall. The surface of the second layer of the outer spore wall is ornamented, having regular, circular pits (1.5-2 microm diam) that are as deep as wide and truncated conical. A "beaded" wall layer as found in most other Acaulospora spp. is lacking. The spore morphology of A. alpina resembles that of A. paulinae but can be differentiated easily by the unique ornamentation with the characteristic pits and by the spore color. A key is presented summarizing the morphological differences among Acaulospora species with an ornamented outer spore wall. Partial DNA sequences of the ITS1, 5.8S subunit and ITS2 regions of ribosomal DNA show that A. alpina and A. paulinae are not closely related. Acaulospora lacunosa, which has similar color but has generally bigger spores, also has distinct rDNA sequences. Acaulospora alpina is a characteristic member of the arbuscular mycorrhizal fungal communities in soils with pH 3.5-6.5 in grasslands of the Swiss Alps at altitudes between 1800 and 2700 m above sea level. It is less frequent at 1300-1800 m above sea level, and it so far has not been found in the Alps below 1300 m or in the lowlands of Switzerland.

Community structure of arbuscular mycorrhizal fungi at different soil depths in extensively and intensively managed agroecosystems.

The vertical distribution of spores of arbuscular mycorrhizal fungi (AMF) was investigated in soil profiles of extensively and intensively managed agroecosystems, including two permanent grasslands, a vineyard and two continuously mono-cropped maize fields. The number of AMF spores decreased with increasing soil depth--most drastically in the grasslands and the vineyard--but there was a large diversity of AMF species even in the deepest soil layers (50-70 cm). This was particularly striking in the maize fields where the highest species numbers were found below ploughing depth. Some species sporulated mainly, or exclusively, in the deep soil layers, others mainly in the top layers. Soil samples were used to inoculate trap cultures. Up to 18 months after inoculation, there was no conspicuous difference in the species composition among the trap cultures representing different soil depths, and only a weak match to the species composition determined by analysis of field samples. Our results indicate that the AMF communities in deep soil layers are surprisingly diverse and different from the topsoil. Thus, deep soil layers should be included in studies to get a complete picture of AMF diversity.

Impact of long-term conventional and organic farming on the diversity of arbuscular mycorrhizal fungi.

Previous work has shown considerably enhanced soil fertility in agroecosystems managed by organic farming as compared to conventional farming. Arbuscular mycorrhizal fungi (AMF) play a crucial role in nutrient acquisition and soil fertility. The objective of this study was to investigate the diversity of AMF in the context of a long-term study in which replicated field plots, at a single site in Central Europe, had been cultivated for 22 years according to two "organic" and two "conventional" farming systems. In the 23rd year, the field plots, carrying an 18-month-old grass-clover stand, were examined in two ways with respect to AMF diversity. Firstly, AMF spores were isolated and morphologically identified from soil samples. The study revealed that the AMF spore abundance and species diversity was significantly higher in the organic than in the conventional systems. Furthermore, the AMF community differed in the conventional and organic systems: Glomus species were similarly abundant in all systems but spores of Acaulospora and Scutellospora species were more abundant in the organic systems. Secondly, the soils were used to establish AMF-trap cultures using a consortium of Plantago lanceolata, Trifolium pratense and Lolium perenne as host plants. The AMF spore community developing in the trap cultures differed: after 12 months, two species of the Acaulosporaceae (A. paulinae and A. longula) were consistently found to account for a large part of the spore community in the trap cultures from the organic systems but were found rarely in the ones from the conventional systems. The findings show that some AMF species present in natural ecosystems are maintained under organic farming but severely depressed under conventional farming, indicating a potentially severe loss of ecosystem function under conventional farming.

Impact of land use intensity on the species diversity of arbuscular mycorrhizal fungi in agroecosystems of Central Europe.

The impact of land use intensity on the diversity of arbuscular mycorrhizal fungi (AMF) was investigated at eight sites in the "three-country corner" of France, Germany, and Switzerland. Three sites were low-input, species-rich grasslands. Two sites represented low- to moderate-input farming with a 7-year crop rotation, and three sites represented high-input continuous maize monocropping. Representative soil samples were taken, and the AMF spores present were morphologically identified and counted. The same soil samples also served as inocula for "AMF trap cultures" with Plantago lanceolata, Trifolium pratense, and Lolium perenne. These trap cultures were established in pots in a greenhouse, and AMF root colonization and spore formation were monitored over 8 months. For the field samples, the numbers of AMF spores and species were highest in the grasslands, lower in the low- and moderate-input arable lands, and lowest in the lands with intensive continuous maize monocropping. Some AMF species occurred at all sites ("generalists"); most of them were prevalent in the intensively managed arable lands. Many other species, particularly those forming sporocarps, appeared to be specialists for grasslands. Only a few species were specialized on the arable lands with crop rotation, and only one species was restricted to the high-input maize sites. In the trap culture experiment, the rate of root colonization by AMF was highest with inocula from the permanent grasslands and lowest with those from the high-input monocropping sites. In contrast, AMF spore formation was slowest with the former inocula and fastest with the latter inocula. In conclusion, the increased land use intensity was correlated with a decrease in AMF species richness and with a preferential selection of species that colonized roots slowly but formed spores rapidly.