| Summary: | The present study provides a deeper insight on variations of microbial abundance and community composition concerning specific environmental parameters related to deadwood decay, focusing on a mesocosm experiment conducted with deadwood samples from black pine of different decay classes. The chemical properties and microbial communities of deadwood changed over time. The total carbon percentage remained constant in the first stage of decomposition, showing a significant increase in the last decay class. The percentage of total nitrogen and the abundances of <i>nifH</i> harbouring bacteria significantly increased as decomposition advanced, suggesting N wood-enrichment by microbial N immobilization and/or N<sub>2</sub>-fixation. The pH slightly decreased during decomposition and significantly correlated with fungal abundance. CO<sub>2</sub> production was higher in the last decay class 5 and positively correlated with bacterial abundance. Production of CH<sub>4</sub> was registered in one sample of decay class 3, which correlates with the highest abundance of methanogenic archaea that probably belonged to <i>Methanobrevibacter</i> genus. N<sub>2</sub>O consumption increased along decomposition progress, indicating a complete reduction of nitrate compounds to N<sub>2</sub> via denitrification, as proved by the highest <i>nosZ</i> gene copy number in decay class 5. Conversely, our results highlighted a low involvement of nitrifying communities in deadwood decomposition.
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