Nematode succession during composting and the potential of the nematode community as an indicator of compost maturity

One of the key issues in compost research is to assess when the compost has reached a mature stage. The maturity status of the compost determines the quality of the final soil amendment product. The nematode community occurring in a Controlled Microbial Composting (CMC) process was analyzed with the objective of assessing whether the species composition could be used as a bio-indicator of the compost maturity status. The results obtained here describe the major shifts in species composition that occur during the composting process. Compared to terrestrial ecosystems, nematode succession in compost differs mainly in the absence of K-strategists and numerical importance of diplogastrids. At the beginning of the composting process (thermophilic phase), immediately after the heat peak, the nematode population is primarily built by bacterial feeding enrichment opportunists (cp-1) (Rhabditidae, Panagrolaimidae, Diplogastridae) followed by the bacterial-feeding general opportunists (cp-2) (Cephalobidae) and the fungal-feeding general opportunists (Aphelenchoididae). Thereafter, during the cooling and maturation stage, the bacterial-feeding-predator opportunistic nematodes (Mononchoides sp.) became dominant. Finally, at the most mature stage, the fungal-feeding Anguinidae (mainly Ditylenchus filimus) were most present. Both, the Maturity Index (MI) and the fungivorous/bacterivorous ratio (f/b ratio), increase as the compost becomes more mature (ranging, respectively, from 1 to 1.86 and from 0 to 11.90). Based on these results, both indices are suggested as potential suitable tools to assess compost maturity.