Display omitted •Intense turnover of organic matter was induced by inoculation of composting piles.•More simple compounds were released from polymeric fractions in inoculated piles.•Humification was more intense and earlier achieved in inoculated piles.•Inoculation clearly stimulated growth and activity of the composting microbiota.•Inoculation affected microbiota structure but its functionality remained unaltered. Enhanced organic matter turnover was detected in lignocellulosic composting piles inoculated with microorganisms specifically capable of decomposing polymeric compounds. In comparison to uninoculated piles, the following results were obtained in the inoculated piles: degradation of hemicellulose, cellulose and lignin were 28%, 21% and 25% respectively higher. Total organic matter, total sugars and phenolic compounds also decreased more intensely. Greater amounts of soluble organic carbon, reducing sugars and soluble proteins were available to the composting microbiota. Recycling of organic to inorganic nitrogen was improved and humification was more intense and earlier attained. Microbial community structure was also affected by inoculation. It was initially thought that these effects were due to enzymatic capabilities of inoculants, however, microbial counts, especially those corresponding to functional groups, revealed that inoculation induced a true stimulation of microbial growth and activity in the entire composting microbiota which was actually responsible for all the beneficial effects reported here.