Soil degradation is defined as a change in the soil health status resulting in a diminished capacity of the ecosystem to provide goods and services for its beneficiaries. Soil degradation is responsible for soil biodiversity loss and in turn for many ecosystem functions disappearance. Many of the functions performed by soil organisms and in particular by microorganisms can provide essential ecosystem services to human society. Most of the species in soil are microorganisms (mainly bacteria and fungi) which are considered the chemical engineers of the soil, responsible for the decomposition of plant organic matter into nutrients readily available for plants, promoting soil fertility and plant productivity. Moreover, they have a key role in soil remediation both in the bulk soil (bioremediation) and in the rhizosphere (Plant-assisted bioremediation). Different threats can act directly on soil biodiversity (e.g. chemical pollution) or indirectly, through one of the soil degradation processes (e.g. land-use change can affect soil biodiversity by favoring erosion). Soil degradation can alter plant productivity, soil resilience and resistance capacity.Mitigation is intervention intended to reduce ongoing degradation. This comes in at a stage when degradation has already begun and the main aim is to halt further degradation and to start improving resources and their functions. The addition of organic matter, through animal or biosolid waste composted, and the restoration of vegetation are suitable strategies to recover and to improve soil condition by erosion and/or contamination. Compost and plant presence can act directly and indirectly to increase microbial diversity and to promote microbial activity and contaminant degradation.In this study we analyzed the role of autochthonous microbial communities in recovering two kinds of degraded soils after applying compost from different sources and/or planting two different species for different purposes (e.g. R. officinalis for improving soil carbon content and M. sativa for PCB degradation). The experimental studies were performed in laboratory microcosms using samples from an agricultural soil degraded with a low organic matter content, and samples from an area chronically contaminated by persistent organic compounds (polychlorinated biphenyls, PCB).The results of the two recovery strategies applied in this work show how the simultaneous application of compost and plant can improve the overall soil quality, promoting the structure and functioning of soil microbial communities and their capability to improve soil quality in terms both of increasing in nutrients and in contaminant decreasing.
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