Loredana Canfora

Salinity and Bacterial Diversity: To What Extent Does the Concentration of Salt Affect the Bacterial Community in a Saline Soil?

In this study, the evaluation of soil characteristics was coupled with a pyrosequencing analysis of the V2-V3 16S rRNA gene region in order to investigate the bacterial community structure and diversity in the A horizon of a natural saline soil located in Sicily (Italy). The main aim of the research was to assess the organisation and diversity of microbial taxa using a spatial scale that revealed physical and chemical heterogeneity of the habitat under investigation. The results provided information on the type of distribution of different bacterial groups as a function of spatial gradients of soil salinity and pH. The analysis of bacterial 16S rRNA showed differences in bacterial composition and diversity due to a variable salt concentration in the soil. The bacterial community showed a statistically significant spatial variability. Some bacterial phyla appeared spread in the whole area, whatever the salinity gradient. It emerged therefore that a patchy saline soil can not contain just a single microbial community selected to withstand extreme osmotic phenomena, but many communities that can be variously correlated to one or more environmental parameters. Sequences have been deposited to the SRA database and can be accessed on ID Project PRJNA241061.

Compartmentalization of gypsum and halite associated with cyanobacteria in saline soil crusts

The interface between biological and geochemical components in the surface crust of a saline soil was investigated using X-ray diffraction, and variable pressure scanning electron microscopy in combination with energy dispersive X-ray spectrometry. Mineral compounds such as halite and gypsum were identified crystallized around filaments of cyanobacteria. A total of 92 genera were identified from the bacterial community based on 16S gene pyrosequencing analysis. The occurrence of the gypsum crystals, their shapes and compartmentalization suggested that they separated NaCl from the immediate microenvironment of the cyanobacteria, and that some cyanobacteria and communities of sulfur bacteria may had a physical control over the distinctive halite and gypsum structures produced. This suggests that cyanobacteria might directly or indirectly promote the formation of a protective envelope made of calcium and sulfur-based compounds.

Routes of phlogopite weathering by three fungal strains

Fungi dissolve soil minerals by acidification and mechanical disruption. Dissolution may occur at the microscale (contact between fungus and mineral) and medium scale (entire mineral grains). Mineral weathering by fungi and other microorganisms is thought to be of significant global contribution, perhaps producing specific weathering signatures. We report fungal dissolution of phlogopite mica in experiments with three fungal strains (Alternaria tenuissima, Cladosporium cladosporioides, Stilbella sp.) on solid medium for 30 days at 21 °C and 96-100% relative humidity. The study used variable-pressure SEM-EDS equipped with charge contrast imaging. Statistical analysis of the results discriminated between the weathering activities of the three fungal species, which increased from Stilbella sp. to C. cladosporioides to A. tenuissima, in agreement with the respective decreasing pH in the media (6.4, 5.8, 5.2 ± 0.03). Phlogopite weathering features were irregular and variable, apparently not caused by direct contact with fungal hyphae. EDS values indicated two or more dissolution mechanisms, one of them suggesting cation rearrangement in the mica towards formation of Al-rich smectite. Intimate fungus-mineral interaction was observed, and the lack of observable dissolution traces from such contact interaction is interpreted as the result of effacing by the more intense acid leaching operating at larger scale.

Risk management tools and the case study Brassica napus: evaluating possible effects of genetically modified plants on soil microbial diversity.

The cultivation of GMPs in Europe raises many questions about the environmental risks, in particular about their ecological impact on non-target organisms and on soil properties. The aim of a multidisciplinary group engaged in a LIFE+project (MAN-GMP-ITA) was to validate and improve an existing environmental risk assessment (ERA) methodology on GMPs within the European legislative framework on GMOs. Given the impossibility of evaluating GMO impact directly, as GMPs are banned in Italy, GMPs have not been used at any stage of the project. The project thus specifically focused on the conditions for the implementation of ERA in different areas of Italy, with an emphasis on some sensitive and protected areas located in the North, Centre, and South of the country, in order to lay the necessary baseline for evaluating the possible effects of a GMP on soil communities. Our sub-group carried out soil analyses in order to obtain soil health and fertility indicators to be used as baselines in the ERA model. Using various methods of chemical, biochemical, functional and genetic analysis, our study assessed the changes in diversity and functionality of bacterial populations, and arbuscular mycorrhizal fungi. The results show that plant identity and growth, soil characteristics, and field site climatic parameters are key factors in contributing to variation in microbial community structure and diversity, thus validating our methodological approach. Our project has come to the conclusion that the uneven composition and biological-agronomical quality of soils need to be taken into consideration in a risk analysis within the framework of ERA for the release of genetically modified plants.

Saline soils in in Italy: distribution, ecological processes and socioeconomic issues

Soils are crucial for crop production and for the major ecosystem services. They preserve and sustain life. Salinity is one of the main soil threats that reduce soil fertility and affect the crop production. In recent times, a great attention has been paid to the general shortage of arable land, and to the increasing demand for ecological restoration of areas affected by secondary salinization processes. Microorganisms in these habitats may share a strategy, may have developed multiple adaptations for maintaining populations, and cope eventually to extreme conditions by altruistic or cooperative behavior for maintaining their population active. The understanding and the knowledge of the composition and distribution of microorganisms in natural habitats can be interesting for ecological reasons and it is important to develop new restoration strategy of salt-affected soils.