Collembolans feeding on soil affect carbon and nitrogen mineralization by their influence on microbial and nematode activities

We manipulated Collembola Folsomia candida Willem density and observed the density effect on carbon and nitrogen mineralization and on nematodes in microcosms filled with mineral soil. Collembolan densities were 0 (control), 25 (low), 100 (medium), and 400 (high) individuals per microcosm. The Collembola enhanced soil respiration and nitrogen mineralization rate in a density-dependent manner (P < 0.05). The correlation between collembolan density and the metabolic quotient of microbes, qCO2, was weakly positive (r = 0.44, P < 0.05). Collembola did not affect microbial biomass. These results suggested that enhanced carbon and nitrogen mineralization was an indirect effect of Collembola mediated by increased microbial activity. Collembola changed the Cnema/Cmic ratio, but only when present at the low density. Thus, Collembola had both positive and negative effects on the nematode population. The positive impact probably depends on the enhancement of microbial activity due to Collembola grazing behavior, while the negative effect appears to result from predation of nematodes.