Microbial bioresources for rehabilitation of natural and anthropogenic deserts

Abstract

Arid lands and deserts cover one fifth of the earth’s land surface and they are currently increasing due to the global warming. Besides the natural desert settings, human activities lead to the desertification of certain areas: municipal landfills and caves are the most common examples of such anthropogenic deserts. Massive pollution and lack of natural soil profiles create harsh conditions and hinder the spontaneous rehabilitation of such areas. Phytoremediation is often used for renaturalization of such degraded soils. Two case studies are presented aiming at demonstrating that the plant-microbe interactions are essential for improving the soil quality and allowing the formation of crops. In the case study of the closed municipall landfill of “Bellolampo” (Sicily, Italy) the performances of newly planted legume shrubs inoculated with selected rhizobial and mychorrizal symbionts, were compared with uninoculated plants. Results showed that microbial symbionts significantly enhanced plant survival and growth. This study demonstrates the importance of the selection procedure aimed to the identification of the best performing strains. Selection of high-performing strains should start with the isolation of microbes from the same region where they will be applied, aiming at exploiting the endemicity, an important feature to increase the chances of soil quality promotion. Moreover, microbial symbionts often show unique metabolic properties due to the co-evolution with the specific host. In natural deserts and arid lands, where few vascular plant species can live, primary colonizers of the barren mineral substrates and suitable hosts for strain selection are lichens. These symbiotic holobionts harbor specific bacterial communities as dense as up to more than 1010 bacterial cells per gram of biomass (dw). These communities are metabolically active and contribute to the survival of the lichen symbiosis in extreme habitats. The wide microbial diversity of the symbioses associated to desert lichens could be a valuable source of new microbial strains particularly suitable for biotechnological applications in arid lands.