Development of a methodology to assess soil carbon stock stability in the presence of microbial activity

Given that carbon is one of the most ubiquitous elements on Earth and plays a crucial role in the global carbon cycle, comprehending the fluxes of carbon among environmental compartments and identifying the factors influencing these fluxes is of fundamental importance. Moreover, the continuous emissions of CO2 and greenhouse gases accentuate the significance of soil, already recognized as one of the Earth's largest carbon reservoirs, as a promising resource to sequester carbon dioxide from the atmosphere in the form of soil organic carbon. With the paradigm shift from the conventional classification of soil organic matter based on humic substances to the emerging framework of the soil continuum model, innovative techniques have been under development to analyse this organic matter. Among these methods, the Rock Eval is a promising technique for quantifying soil organic matter and assessing its stability. This method involves a pyrolysis followed by combustion of a desiccated sample and was initially created for evaluating the petroleum potential of geological sources. In recent years, it has found application in studying the dynamics and persistence of soil organic carbon in the environment. The core objective of this research project is to use the Rock Eval technique to establish a methodology for investigating the impact of various microorganisms on soil organic matter. This study represents the initial phase of a broader research aimed at producing microbial consortia able to increase carbon storage in soils. To achieve this, distinct microorganisms, both bacteria and fungi, were introduced into sterilized laboratory-prepared soils of varying textures, supplied with a readily available source of nutrients, and maintained at a constant temperature for one month. Samples were taken at the beginning and conclusion of the incubation period and analysed with the Rock Eval method for total organic carbon and its stability. Furthermore an attempt was done to analyse the composition of the TOC in terms of Water Extractable Organic Carbon and Nitrogen, mineralogical and particulate fractions. The results derived from the Rock Eval method revealed a decrease in the total organic carbon (TOC), as anticipated due to bacterial proliferation, followed by an enhancement in the thermal stability of the organic matter in certain samples. The methodology developed can be applied to future investigations involving more complex soil types and microbial communities, supporting the identification of optimal microbial consortia to enhance carbon sequestration in soil.