Diversity of arbuscular mycorrhizal fungi in Brazil's Caatinga and experimental agroecosystems

Richness of Arbuscular Mycorrhizal Fungi in a Brazilian Tropical Shallow Lake: Assessing an Unexpected Assembly in the Aquatic-Terrestrial Gradient

Aquatic ecosystems are historically overlooked regarding the occurrence of Arbuscular Mycorrhizal Fungi (AMF). Tropical lakes in the southern hemisphere are generally impacted by human actions, such as those in Brazil, although they still preserve a great diversity of macrophyte species that can support AMF communities. Thus, the study aimed to test (i) whether AMF community structure (composition, richness, diversity, dominance, and evenness) differs between aquatic and terrestrial conditions, and (ii) between seasons—rainy and dry. A total of 60 AMF species, distributed in 10 families and 17 genera, were found, with a difference in AMF composition between conditions (terrestrial and aquatic) and seasons (dry and rainy). The absolute species richness differed between conditions, seasons, and interactions. The aquatic/rainy season, which retrieved the most significant number of species, had the highest absolute richness and number of glomerospores and differed significantly from the terrestrial/rainy season. The results suggest that a shallow oligotrophic lake harbors a high AMF richness. In addition, this environment has a distinct AMF community from the adjacent coastal sand plain vegetation and is affected by seasonality.

Arbuscular Mycorrhizal Fungal Community Structure in the Rhizosphere of Three Plant Species of Crystalline and Sedimentary Areas in the Brazilian Dry Forest

The Brazilian dry forest (Caatinga) is located in one of the world's largest tropical semiarid regions, and it occurs on two large geological environments named the crystalline and sedimentary basins. In order to determine the structure and the main drivers of the composition of communities of arbuscular mycorrhizal fungi (AMF) in the Caatinga, we collected soil samples from the rhizosphere of Jatropha mollissima, J. mutabilis, and Mimosa tenuiflora, species that occur in crystalline and sedimentary areas. Ninety-six AMF taxa were identified from soils collected directly in the field and trap cultures. Acaulospora, Glomus, and Rhizoglomus represented almost 49% of the taxon richness. The composition of the AMF communities differed between the crystalline and sedimentary areas and between the rhizospheres of the three plant species. Coarse sand, total sand, natural clay, calcium, soil particles density, flocculation, pH, and base saturation were the principal edaphic variables related to the distribution of these organisms. We registered nine and 17 AMF species classified as indicators, for the geological environments and plant species, respectively. Glomerospores of Glomerales predominated in crystalline basins, whereas glomerospores of Gigasporales prevailed in sedimentary areas; among the plant species, lower number of glomerospores of Archaeosporales and Glomerales was recorded in the rhizosphere of J. mollissima. The results show that the AMF community composition is shaped by geological environments and plant hosts. In addition, soil characteristics, mainly physical attributes, significantly influence the structure of Glomeromycota communities occurring in areas of the Brazilian semiarid.

Arbuscular Mycorrhizal Fungal Assemblages in Conservation Unit of Atlantic Forest Areas Under Native Vegetation and Natural Regeneration

Arbuscular mycorrhizal fungi (AMF) play an important role in the dynamic of plant community in the south American Atlantic Rainforest biome. Even in protected areas, this biome is under several anthropic impacts, which can cause shifts in the soil microbiota, including AMF. This study aimed to determine the structure and composition of AMF community in areas of native Atlantic Forest and in natural regeneration and to identify which abiotic factors are influencing this community in these areas. Soil samples were collected at Monte Pascoal National and Historical Park, in Southern Bahia, in native and natural regeneration areas of Atlantic Forest in two seasons (rainy and dry). Greater number of glomerospores and richness and diversity of AMF were found in the area under regeneration, with differences between seasons being observed only for the number of glomerospores. Seventy-seven species of AMF were recorded, considering all areas and seasons, with Acaulospora and Glomus being the most representative genera. Greater abundance of species of the genera Acaulospora, Claroideoglomus, and Septoglomus was found in the regeneration area. The AMF community differed between the study areas, but not between seasons, with soil attributes (pH, K, Al, Mg, m, and clay) structuring factors for this difference in the AMF community. Atlantic Forest areas in natural regeneration and the soil edaphic factors provide changes in the structure and composition of the AMF community, increasing the richness and diversity of these fungi in conservation units.

Mycorrhizal fungal community structure in tropical humid soils under fallow and cropping conditions

Little is known to what extent soil biota, in particular, the mycorrhizae are altered through different fallow durations/types in tropical soils. We found that soil-N, -C, -Al, -K and -Ca contents significantly differed due to the fallow durations/types. Subsequently, the effects of fallow types and soil depths on the diversity, species richness and community structure of arbuscular mycorrhizal (AM) fungi were examined. A higher AM species richness was identified in the cropping than in forest fallow fields, suggesting a positive cropping feedback on the AM community composition. Distribution of the AM species was positively related to soil properties, specifically soil-pH, and soil-Pi, -Ca and -Mg contents. The soil properties conjointly accounted for 78.5% of explained variation in the AM community composition, signifying that the main factors altering the community structure under different fallow and cropping systems were the soil properties. Among the soil chemical characteristics, the soil-pH disclosed a significant explained variation in the AM community composition in the topsoil layer under the short fallow. Structural modeling equation to understand multiple predictive pathways that connect soil properties, fallow practices and AM community structures indicated that soil-C, -N and -Ca contents were highlighted as important factors influencing the AM community compositions.

Predictors of Arbuscular Mycorrhizal Fungal Communities in the Brazilian Tropical Dry Forest

Arbuscular mycorrhizal fungi (AMF) are symbiotic fungi with a broad distribution, and many taxa have physiological and ecological adaptations to specific environments, including semiarid ecosystems. Our aim was to address regional distribution patterns of AMF communities in such semiarid environments based on spore morphological techniques. We assessed AMF spores at the bottom and top of inselbergs distributed throughout the tropical dry forest in the Northeast region of Brazil. Across 10 replicate inselbergs and the surrounding area, spanning a range of altitude between 140 and 2000 m, we scored the AMF soil diversity and properties in 52 plots. We fitted parsimonious ordination analyses and variance partitioning models to determine the environmental factors which explained the variation in AMF community, based on morphological spore analysis. The diversity of AMF was similar at the bottom and top of inselbergs; however, we detected high variation in abundance and richness across sites. We formulated a parsimonious richness model that used physical soil factors as predictors. The AMF community structure could be best explained through the variables coarse and total sand, iron, organic matter, potassium, silt, and sodium which together accounted for 17.8% of total variance. Several AMF species were indicators of either deficiency or high values of specific soil properties. We demonstrated that habitat isolation of the inselbergs compared with surrounding areas did not trigger differences in AMF communities in semiarid regions of Brazil. At the regional scale, soil predictors across sites drove the distribution of symbiotic mycorrhizal fungi.