Characterization of Rhizobia and Arbuscular Mycorrhizal Fungi in Areas Impacted by Gravel Mining in Brazil

Abstract

On-shore oil exploration is one of the main economic activities in the semiarid region (Caatinga biome) of the state of Rio Grande do Norte (RN), Brazil. Gravel mining is an activity associated with oil exploration that causes environmental impacts. Gravel is a base-material for constructions, such as roads and pumpjack bases. The areas of gravel mining and other decommissioned areas where the gravel has been deposited must be revegetated with species native to the biome at end of the activity in the site. An efficient strategy for revegetation of degraded areas has been the planting of leguminous species that can associate with rhizobia and arbuscular mycorrhizal fungi (AMF). Nevertheless, the impact of mining activities on the autochthonous populations of these microorganisms is unknown. The objective of the present work is to characterize the density of rhizobia and AMF spores in four areas impacted by the oil exploration in RN when compared to non-impacted adjacent areas. Gravel samples were collected in dry and rainy seasons in two mining areas: one in a pumpjack base, and one in a waste disposal area. Surface soil (topsoil) samples were collected in adjacent areas with native Caatinga vegetation. Assays were carried out to evaluate the most probable number (MPN) of rhizobia and to identify the type and density of arbuscular mycorrhizal fungi (AMF), using rhizobia trap plants Mimosa tenuiflora (Mart.) Benth. and Mimosa caesalpiniifolia Benth. The MPN of rhizobia was low in all areas, but higher in the rainy season. The highest amount and diversity of AMF spores were found in the dry season. Among the symbiotic microorganisms studied, the AMF presented lower densities in the evaluated areas when compared to those in the adjcent native vegetation areas, denoting the impact of this activity.

Monitoring of Nematofauna and Arbuscular Mycorrhizal Fungi in a Caatinga Area and in the Adjacent Culture

“…In general, the Caatinga areas have greater diversity, being greater in the dry season (Silva et al, 2019;Pagano et al, 2013), however, in the present work there was no difference in relation to the collection periods and areas, apparently the amount of AMF species was similar between the Caatinga area and the cultivation area.…”

“…Thus, in relation to the similarity of species between areas, the cultivation and the Caatinga edge presented similar results, which may be associated with the proximity of the Caatinga edge to the cultivation. Vegetation, seasonal variations and soil type affect AMF diversity, however, soil is considered a key factor for the similarity or dissimilarity of AMF communities between Caatinga areas (Silva et al, 2019).…”

Editorial: Rocks, plants, and microbes, volume II

“…On the other hand, they will also heavily depend on microbial activity to release nutrients for plant establishment. In this scenario, arbuscular mycorrhizae fungi (AMF) play a central role by providing plant access to poorly soluble, low-diffusion nutrients, such as phosphorus, through hyphal networks ( Silva et al., 2019 ). Shen et al.…”

“…On the other hand, they will also heavily depend on microbial activity to release nutrients for plant establishment. In this scenario, arbuscular mycorrhizae fungi (AMF) play a central role by providing plant access to poorly soluble, low-diffusion nutrients, such as phosphorus, through hyphal networks (Silva et al, 2019). Shen et al used Bidens pilosa L., a typical pioneer succession species, as a plant model to study how AMF regulates plant growth and nutrient utilization under patchy habitats with varying soil compositions in the karst ecosystem.…”