Decomposition in the school compost and the role that arthropods play in this is a constant source of concern for the school’s custodians and groundskeepers. The goal of this study was to ascertain what role arthropods play in the decomposition process, if any. We conducted a 3-month litterbag study on the compost pile at Phoenix College. We used litterbags containing air dried leaves of Arizona sycamore (Platanus wrightii) with three different mesh sizes to either allow or exclude parts of the invertebrate community and measured the resulting changes in litter chemistry during decomposition. A 75 μm mesh size was used to allow microbial access and water infiltration; a 1.5 mm mesh to allow microarthropods access; and a 3 mm mesh was used to allow all arthropods access. Litterbags were placed into the center of the compost pile in early May. At 3, 6, 9, and 12 weeks, four replicate litterbags were collected from each mesh size. We collected the invertebrates and quantified the microbial community. Lignin, cellulose, and hemicellulose content, as well as phosphorus, carbon, nitrogen and other micronutrient content (Ca, K, Mg and Na) was measured.
Initial results indicate that the compost pile at Phoenix College is richly populated by arthropods, with all levels of the soil foodweb represented. Overall density of microarthropods was approximately 3,000 individuals kg-1 dry compost, and included a large abundance of termites, Collembola, mites, isopods, Diptera and Coleoptera larvae, as well as lower densities of earwigs, spiders, pseudoscorpions, and more. Over the course of the experiment, there was a dry mass loss of 20%-30% with some variation by mesh size. The rate of decomposition appeared higher in the small mesh size bags and slower in the larger size mesh, indicating that arthropods might play some role in moving the dry mass around the pile, including possibly into the litterbags. Nutrient assimilation and release during decomposition also differed with mesh sizes. Litter bags with smaller mesh size were lower in phosphorous, calcium and magnesium, perhaps indicating lower assimilation of nutrients by the microbial community on the litter in the absence of arthropods. The results on carbon, nitrogen and the microbial community are forthcoming. This study provides insight into the chemistry of litter as it goes through the composting process and how biota beyond microbes might influence it.