In Sustainable Forest Management, decaying wood plays an important role in forest biodiversity, carbon balance and nutrient cycling. The management of this important component of forest ecosystems is limited by the fact that little is known about relationships between substrate quality and community structure of wood-inhabiting microorganisms. During decomposition, carbon stored in deadwood is lost either in the atmosphere or in the soil, but to our knowledge, limited information on the quantities of CO 2 and other greenhouse gases (GHG) emitted is available.In the present research we investigated the correlation between the decay of logs, the decomposer microorganisms and their activities, in terms of GHG production and enzymes, in a black pine (Pinus nigra Arnold ssp. nigra) degraded forest. The decomposition of deadwood was visually assessed using a five-class system, and for each decay class four wood samples were collected. CO 2 , CH 4 and N 2 O potential production from each decay class was measured in closed systems by means of gas chromatography. Enzyme activities related to carbon, nitrogen, sulphur and phosphorus cycling were measured fluorometrically. The composition of decomposer microbial communities (fungi, bacteria and actinobacteria) was assessed by using polymerase chain reaction-denaturing gradient gel electrophoresis fingerprinting. CO 2 production and enzyme activities were significantly higher in the last decay classes of deadwood. The molecular approach highlighted differences in microbial community structure both at species and abundance levels, depending on the rate of decay.

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