Occurrence and diversity of arbuscular mycorrhizal fungi in trap cultures from soils under different land use systems in the Amazon, Brazil

Arbuscular Mycorrhizal Fungal Community Composition in Carludovica palmata, Costus scaber and Euterpe precatoria from Weathered Oil Ponds in the Ecuadorian Amazon

Arbuscular mycorrhizal fungi (AMF) are ubiquitous to most natural and anthropized ecosystems, and are often found in polluted environments. However, their occurrence and community composition in highly weathered petroleum-polluted soils has been infrequently reported. In the present study, two ponds of weathered crude oil and their surrounding soil from the Charapa field in the Amazon region of Ecuador were selected and root colonization by AMF of their native plants investigated. The AMF community was further analyzed in three selected plant species (i.e., Carludovica palmata, Costus scaber and Euterpe precatoria) present in the two ponds and the surrounding soil. A fragment covering partial SSU, the whole ITS and partial LSU rDNA region was amplified (i.e., 1.5 kb), cloned and sequenced from the roots of each host species. AMF root colonization exceeded 56% in all plant species examined and no significant difference was observed between sites or plants. For AMF community analysis, a total of 138 AMF sequences were obtained and sorted into 32 OTUs based on clustering (threshold ≥97%) by OPTSIL. The found OTUs belonged to the genera Rhizophagus (22%), Glomus (31%), Acaulospora (25%) and Archaeospora (22%). Glomus and Archaeospora were always present regardless of the plant species or the site. Acaulospora was found in the three plant species and in the two ponds while Rhizophagus was revealed only in the surrounding soil in one plant species (Euterpe precatoria). Our study contributed to the molecular community composition of AMF and revealed an unexpected high presence of four AMF genera which have established a symbiosis with roots of native plants from the Amazon forest under high polluted soil conditions.

Enrichment of arbuscular mycorrhizal fungi in a contaminated soil after rehabilitation

Spore counts, species composition and richness of arbuscular mycorrhizal fungi, and soil glomalin contents were evaluated in a soil contaminated with Zn, Cu, Cd and Pb after rehabilitation by partial replacement of the contaminated soil with non-contaminated soil, and by Eucalyptus camaldulensis planting with and without Brachiaria decumbens sowing. These rehabilitation procedures were compared with soils from contaminated non-rehabilitated area and non-contaminated adjacent soils. Arbuscular mycorrhizal fungi communities attributes were assessed by direct field sampling, trap culture technique, and by glomalin contents estimate. Arbuscular mycorrhizal fungi was markedly favored by rehabilitation, and a total of 15 arbuscular mycorrhizal fungi morphotypes were detected in the studied area. Species from the Glomus and Acaulospora genera were the most common mycorrhizal fungi. Number of spores was increased by as much as 300-fold, and species richness almost doubled in areas rehabilitated by planting Eucalyptus in rows and sowing B. decumbens in inter-rows. Contents of heavy metals in the soil were negatively correlated with both species richness and glomalin contents. Introduction of B. decumbens together with Eucalyptus causes enrichment of arbuscular mycorrhizal fungi species and a more balanced community of arbuscular mycorrhizal fungi spores in contaminated soil.

Links between plant and fungal communities across a deforestation chronosequence in the Amazon rainforest

Understanding the interactions among microbial communities, plant communities and soil properties following deforestation could provide insights into the long-term effects of land-use change on ecosystem functions, and may help identify approaches that promote the recovery of degraded sites. We combined high-throughput sequencing of fungal rDNA and molecular barcoding of plant roots to estimate fungal and plant community composition in soil sampled across a chronosequence of deforestation. We found significant effects of land-use change on fungal community composition, which was more closely correlated to plant community composition than to changes in soil properties or geographic distance, providing evidence for strong links between above- and below-ground communities in tropical forests.

Arbuscular mycorrhizal fungal communities along a pedo-hydrological gradient in a Central Amazonian terra firme forest

Little attention has been paid to plant mutualistic interactions in the Amazon rainforest, and the general pattern of occurrence and diversity of arbuscular mycorrhizal fungi (AMF) in these ecosystems is largely unknown. This study investigated AMF communities through their spores in soil in a 'terra firme forest' in Central Amazonia. The contribution played by abiotic factors and plant host species identity in regulating the composition, abundance and diversity of such communities along a topographic gradient with different soils and hydrology was also evaluated. Forty-one spore morphotypes were observed with species belonging to the genera Glomus and Acaulospora, representing 44 % of the total taxa. Soil texture and moisture, together with host identity, were predominant factors responsible for shaping AMF communities along the pedo-hydrological gradient. However, the variability within AMF communities was largely associated with shifts in the relative abundance of spores rather than changes in species composition, confirming that common AMF species are widely distributed in plant communities and all plants recruited into the forest are likely to be exposed to the dominant sporulating AMF species.

Loss of arbuscular mycorrhizal fungal diversity in trap cultures during long-term subculturing

Long-term successional dynamics of an inoculum of arbuscular mycorrhizal fungi (AMF) associated with the maize rhizosphere (from traditionally managed agroecosystems in Los Tuxtlas, Veracruz, Mexico), was followed in Bracchiaria comata trap cultures for almost eight years. The results indicate that AMF diversity is lost following long-term subculturing of a single plant host species. Only the dominant species, Claroideoglomus etunicatum, persisted in pot cultures after 13 cycles. The absence of other morphotypes was demonstrated by an 18S rDNA survey, which confirmed that the sequences present solely belonged to C. etunicatum. Members of Diversisporales were the first to decrease in diversity, and the most persistent species belonged to Glomerales.

Microbial activity, arbuscular mycorrhizal fungi and inoculation of woody plants in lead contaminated soil

The goals of this study were to evaluate the microbial activity, arbuscular mycorrhizal fungi and inoculation of woody plants (Caesalpinia ferrea, Mimosa tenuiflora and Erythrina velutina) in lead contaminated soil from the semi-arid region of northeastern of Brazil (Belo Jardim, Pernambuco). Dilutions were prepared by adding lead contaminated soil (270 mg Kg^-1) to uncontaminated soil (37 mg Pb Kg soil^-1) in the proportions of 7.5%, 15%, and 30% (v:v). The increase of lead contamination in the soil negatively influenced the amount of carbon in the microbial biomass of the samples from both the dry and rainy seasons and the metabolic quotient only differed between the collection seasons in the 30% contaminated soil. The average value of the acid phosphatase activity in the dry season was 2.3 times higher than observed during the rainy season. There was no significant difference in the number of glomerospores observed between soils and periods studied. The most probable number of infective propagules was reduced for both seasons due to the excess lead in soil. The mycorrhizal colonization rate was reduced for the three plant species assayed. The inoculation with arbuscular mycorrhizal fungi benefited the growth of Erythrina velutina in lead contaminated soil.