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.A main component of the soil microbiota in most agroecosystems are the arbuscular mycorrhizal fungi (AMF). These obligate mutualistic symbionts colonize the roots of the vast majority of plants, including most crop plants (50). By forming an extended, intricate hyphal network, AMF can efficiently absorb mineral nutrients from the soil and deliver them to their host plants in exchange for carbohydrates. Facilitated nutrient uptake, particularly with respect to immobile nutrients, such as phosphorus, is believed to be the main benefit of the mycorrhizal symbiosis for plants (20,39). AMF can also enhance tolerance of or resistance to root pathogens (7) or abiotic stresses, such as drought and metal toxicity (37). Furthermore, AMF may play a role in the formation of stable soil aggregates, building up a macroporous structure of soil that allows penetration of water and air and prevents erosion (39).From all of these beneficial effects on plant performance and soil health, it is evident that AMF are crucial for the functioning of terrestrial ecosystems. Not only their presence but also their genetic and functional diversities are of importance: AMF diversity can be decisive for both plant community s...

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.

No abstract

Summary• 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.

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. Sensu lato, 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.

No abstract

Summary Greenhouse and field experiments were conducted on the effect of VA mycorrhiza (V AM) on the growth of cassava, various tropical grass and legume speCies, as well as beans, coffee and tea. A large number of V AM fungal species were evaluated for effectivity in increasing cassava growth and P uptake in acid low-P soils. The effectivity of VAM species and isolates was highly variable and dependent on soil pH and fertilizer applications, as well as on soil temperature and humidity. Two species, Glomus manihotis and Entrophospora colombiana were found to be most effective for a range of crops and pastures, at low pH and at a wide range of N, P, and K levels.At very low P levels nearly all crops and pasture species were highly mycorrhizal dependent, but at higher soil P levels cassava and several pasture legumes were more dependent than grass species.Mycorrhizal inoculation significantly increased cassava and bean yields in those soils with low or ineffective indigenous mycorrhizal populations. In these soils cassava root yields increased on the average 20-25% by V AM inoculation, both at the experiment station and in farmers' fields. V AM inoculation of various pasture legumes and grasses, in combination with rock phosphate applications, increased their early growth and establishment. Agronomic practices such as fertilization, crop rotations, intercropping and pesticide applications were found to affect both the total V AM population as well as its species composition.While there is no doubt about the importance of VA mycorrhizain enhancing P uptake and growth of many tropical crops and pastures grown on low-P soils, much more research is required to elucidate the complicated soil-plant-V AM interactions and to increase yields through improved mycorrhizal efficiency.

Species in the orders Glomerales and Diversisporales (Glomeromycetes) with glomoid spore formation are reorganized based on combined ribosomal sequence and morphological analyses. Within the Glomerales two genera in the Glomeraceae (Septoglomus, Simiglomus) and one genus in the Claroideoglomeraceae (Viscospora) are proposed as new. Paraglomerales species (thus far monogeneric) also form glomoid spores that may all germinate directly through the spore wall instead through subtending hyphae as in Glomerales.