Assessing the influence of topsoil and technosol characteristics on plant growth for the green regeneration of urban built sites.

Achieving urban regeneration through the creation of new green areas is a widely promoted strategy to improve the quality of life in densely built neighborhoods. "De-sealing" actions can compensate for the creation of new built-up areas, as demonstrated by the EU-funded Life + project 'Save our Soils for LIFE' (SOS4LIFE, LIFE15ENV/IT/000225), in which guidelines for de-sealing have been published. For the generation of new urban greening, it is important to know the characteristics of the soils used in order to better define the most appropriate landscaping decisions and management practices. In this study the physical and chemical characteristics of topsoils and technosols (soils enclosed under sealed surfaces) were assessed in relation to growth and leaf gas exchanges in two ornamental species (V. tinus and E. x ebbingei), in two partner municipalities of the project, Carpi and San Lazzaro di Savena (north-east Italy), during a three-year trial. Results of the study confirmed the dependence of plant growth on the chemical evolution of the soils, and identified the optimal soil moisture range based on soil texture and soil-plant water relationships. In addition, the technosols were found to actually be beneficial for plant growth, due to their high drainage capacity and nutrient content.

Microbiomes in Soils Exposed to Naturally High Concentrations of CO2 (Bossoleto Mofette Tuscany, Italy).

Direct and indirect effects of extremely high geogenic CO2 levels, commonly occurring in volcanic and hydrothermal environments, on biogeochemical processes in soil are poorly understood. This study investigated a sinkhole in Italy where long-term emissions of thermometamorphic-derived CO2 are associated with accumulation of carbon in the topsoil and removal of inorganic carbon in low pH environments at the bottom of the sinkhole. The comparison between interstitial soil gasses and those collected in an adjacent bubbling pool and the analysis of the carbon isotopic composition of CO2 and CH4 clearly indicated the occurrence of CH4 oxidation and negligible methanogenesis in soils at the bottom of the sinkhole. Extremely high CO2 concentrations resulted in higher microbial abundance (up to 4 × 109 cell g-1 DW) and a lower microbial diversity by favoring bacteria already reported to be involved in acetogenesis in mofette soils (i.e., Firmicutes, Chloroflexi, and Acidobacteria). Laboratory incubations to test the acetogenic and methanogenic potential clearly showed that all the mofette soil supplied with hydrogen gas displayed a remarkable CO2 fixation potential, primarily due to the activity of acetogenic microorganisms. By contrast, negligible production of acetate occurred in control tests incubated with the same soils, under identical conditions, without the addition of hydrogen. In this study, we report how changes in diversity and functions of the soil microbial community - induced by high CO2 concentration - create peculiar biogeochemical profile. CO2 emission affects carbon cycling through: (i) inhibition of the decomposition of the organic carbon and (ii) promotion of CO2-fixation via the acetyl-CoA pathway. Sites naturally exposed to extremely high CO2 levels could potentially represent an untapped source of microorganisms with unique capabilities to catalytically convert CO2 into valuable organic chemicals and fuels.

Testing decontaminated sediments as a substrate for ornamentals in field nursery plantations.

When canals and harbours are dredged, huge amount of polluted sediments has to be stocked and transported to the landfill with incredibly high costs of management. Among the remediation techniques for the reclamation of polluted sediments and soils, phytoremediation represents a sustainable and effective technique though still not fully promoted or commercialized. In this study we have tested the suitability for plant nursing of a substrate resulting from sediments dredged from a canal and treated with phytoremediation. The experiment was set up in 2014. It aimed to test the physical, chemical and hydrological characteristics of two mixes of remediated sediments and agronomic soil (at 33% and 50% by volume) compared to control soil (100% agronomic soil), and to assess the growth of three ornamental species (Viburnum tinus L., Photinia x fraseri var. red robin, Eleagnus macrophylla Thunb.) together with the suitability for root balling. The mixed substrates produced good results in terms of water drainage, and were similar to the control in terms of soluble nutrients, guaranteeing and enhancing the aboveground and belowground growth of all the three species, especially V. tinus. In contrast, mixed substrates impaired root ball compaction with root ball breakage observed especially in 50% sediment/soil mix. Therefore, the use of remediated sediments in plant nursery can be limited to specific productions or practices.

Carbon sequestration and fertility after centennial time scale incorporation of charcoal into soil.

The addition of pyrogenic carbon (C) in the soil is considered a potential strategy to achieve direct C sequestration and potential reduction of non-CO2 greenhouse gas emissions. In this paper, we investigated the long term effects of charcoal addition on C sequestration and soil physico-chemical properties by studying a series of abandoned charcoal hearths in the Eastern Alps of Italy established in the XIX century. This natural setting can be seen as an analogue of a deliberate experiment with replications. Carbon sequestration was assessed indirectly by comparing the amount of pyrogenic C present in the hearths (23.3±4.7 kg C m(-2)) with the estimated amount of charcoal that was left on the soil after the carbonization (29.3±5.1 kg C m(-2)). After taking into account uncertainty associated with parameters' estimation, we were able to conclude that 80±21% of the C originally added to the soil via charcoal can still be found there and that charcoal has an overall Mean Residence Time of 650±139 years, thus supporting the view that charcoal incorporation is an effective way to sequester atmospheric CO2. We also observed an overall change in the physical properties (hydrophobicity and bulk density) of charcoal hearth soils and an accumulation of nutrients compared to the adjacent soil without charcoal. We caution, however, that our site-specific results should not be generalized without further study.