Composting processes largely depends on microbial activity, but a small amount of data is available about the role of different microbial groups and the potential use of mature composts based on highly lignocellulosic organic materials. In this work microbiological and physico-chemical analyses were carried out aiming to evaluate microbial, physiological and agronomic characteristics of a novel kind of compost obtained from chestnut wastes and used as substrate for tomato (Lycopersicon esculentum Mill.) seedling production. After 345 days of composting, mature compost showed a temperature of 24 A degrees C, pH of 6.9, and a water activity of 0.95. Microbial characterization of hemicellulolytic, cellulolytic and ligninolytic groups in compost showed a different trend during composting process but all were found at a high concentration in the mature compost (10(6)-10(7) CFU g(-1)), as well as free-living (N-2)-fixing bacteria and Pseudomonas spp. Porosity was 58%, while the value of water holding capacity and compost moisture reached 290 mL L-1 and 40.8%, respectively. Our compost used as substrate for tomato growth, elicited on plantlets a reduction of pigments (chlorophylls and carotenoids) especially for chlorophyll a (594.45 +/- 30.25 mu g g(-1) FW) compared to the control (1064.52 +/- 55.05 mu g g(-1) FW). Moreover, the compost markedly influenced plant antioxidants capacity and stress response observing an increase of the catalase from 17.4 +/- 0.15 to 20.3 +/- 0.84 A mu mol H2O2 min(-1) mg(-1) protein, ascorbate peroxidase activity from 1135 +/- 33 to 3213 +/- 52 A mu mol AsA min(-1) mg(1) protein and ascorbate oxidase activity from 313 +/- 8.2 to 1840 +/- 29 A mu mol AsA min(-1) mg(1) protein in plants grown on 100% peat and 100% compost, respectively.