RESUMEN

In Mexico, millions of tons of mining wastes are deposited in the open pit. Their content in potentially toxic elements (PTE) represents an environmental risk. In the tailings, pioneer plant communities are established, associated with a determined diversity of fungi; plants, and fungi are fundamental in the natural rehabilitation of mining wastes. The objective was to evaluate the impact of the natural establishment of two plant species on the microbial activity, on the composition of the fungal community, and on the mitigation of the effect of PTE in a contaminated mine tailing. In a tailing, we selected three sites: one non-vegetated; one vegetated by Reseda luteola, and one vegetated by Asphodelus fistulosus. In the substrates, we conducted a physical and chemical characterization; we evaluated the enzymatic activity, the mineralization of the carbon, and the concentration of PTE. We also determined the fungal diversity in the substrates and in the interior of the roots, and estimated the accumulation of carbon, nitrogen, phosphorus and PTE in plant tissues. The tailings had a high percentage of sand; the non-vegetated site presented the highest electric conductivity, and the plant cover reduced the concentration of PTE in the substrates. Plants increased the carbon content in tailings. The enzymatic activities of ß-glucosidase and dehydrogenase, and the mineralization of carbon were highest at the site vegetated with A. fistulosus. Both plant species accumulated PTE in their tissues and exhibited potential in the phytoremediation of lead (Pb), cadmium (Cd), and copper (Cu). Fungal diversity was more elevated at the vegetated sites than in the bare substrate. Ascomycota prevailed in the substrates; the substrates and the plants shared some fungal taxa, but other taxa were specific. The plant coverage and the rhizosphere promoted the natural attenuation and a rehabilitation of the extreme conditions of the mining wastes, modulated by the plant species.

Asunto(s)

Metales Pesados , Micobioma , Contaminantes del Suelo , Metales Pesados/análisis , Minería , Plantas , Rizosfera , Suelo , Contaminantes del Suelo/análisis

RESUMEN

BACKGROUND: Global demand for food has led to increased land-use change, particularly in dry land ecosystems, which has caused several environmental problems due to the soil degradation. In the Cuatro Cienegas Basin (CCB), alfalfa production irrigated by flooding impacts strongly on the soil. METHODS: In order to analyze the effect of such agricultural land-use change on soil nutrient dynamics and soil bacterial community composition, this work examined an agricultural gradient within the CCB which was comprised of a native desert grassland, a plot currently cultivated with alfalfa and a former agricultural field that had been abandoned for over 30 years. For each site, we analyzed C, N and P dynamic fractions, the activity of the enzyme phosphatase and the bacterial composition obtained using 16S rRNA clone libraries. RESULTS: The results showed that the cultivated site presented a greater availability of water and dissolved organic carbon, these conditions promoted mineralization processes mediated by heterotrophic microorganisms, while the abandoned land was limited by water and dissolved organic nitrogen. The low amount of dissolved organic matter promoted nitrification, which is mediated by autotrophic microorganisms. The microbial N immobilization process and specific phosphatase activity were both favored in the native grassland. As expected, differences in bacterial taxonomical composition were observed among sites. The abandoned site exhibited similar compositions than native grassland, while the cultivated site differed. DISCUSSION: The results suggest that the transformation of native grassland into agricultural land induces drastic changes in soil nutrient dynamics as well as in the bacterial community. However, with the absence of agricultural practices, some of the soil characteristics analyzed slowly recovers their natural state.