N cycle in burnt and unburnt soils under different vegetation covers in the Mediterranean region

The Mediterranean area is a fragile semi-arid ecosystem, characterized by a high level of biodiversity. Due to its climatic conditions, fires are frequent. Fires strongly impact the microbial community of the soil and the biogeochemical cycles of the ecosystem. Although the N cycle is crucial, limited data is available about the effects of fires on the microbial community involved in this cycle in these types of environments. The aim of this research was to evaluate the effects that fire has on the amount of microbial populations involved in the different steps of the N cycle in soils under different vegetation cover. To achieve this, surface soils were collected from unburnt and burnt soil of four plant species (holm oak, pine, black locust, and herbs) from inside the Vesuvius National Park that are typical of the Mediterranean maquis. The soils were analyzed for their main abiotic proprieties (pH, water content, concentrations of organic C, total C, total N, NH4+, NO2–, and NO3–). They were also analyzed for their amount of total DNA (DNA yield), eubacterial DNA (16S rDNA), N2-fixer, ammonia oxidizer, archaea ammonia oxidizer, and denitrifier DNA. The largest amount of microbial populations involved in the N cycle of the unburnt soil was observed in the holm oak soil. Fires slightly affected the soil abiotic properties and the DNA yield of the unburnt soil, but significantly increased the amount of eubacteria, nitrifiers, and denitrifiers. The conditions of the pine and holm oak soil encouraged a faster recovery of the amount of microbial populations involved in the N cycle.