The effects of collembola grazing on microbial activity in decomposing leaf litter

Ground leaf litter was inoculated with the fungus Coriolus versicolor and incubated in respirometers for 6 days ("fresh" cultures) or 33 days ("senescent" cultures) before different number of Folsomia candida were added. Grazing by 5 animals stimulated O₂ consumption in both series of cultures but 10, 15 or 20 animals inhibited microbial respiration. The stimulatory effect was less marked in the senescent cultures. Bacterial and fungal standing crops increased in "fresh" cultures during the course of the experiment but grazing by collembola increased bacterial and reduced fungal standing, crops in proportion to the grazing intensity. Microbial standing crops were not determined for senescent cultures. Microarthropod feeding activities can therefore exert a strong differential effect on fungal and bacterial populations which has not been previously recognised.