Microarthropods

In most soils, 90% of the microarthropod population is composed of Collembola (springtails)

and Acari (mites), while the remainder includes Protura, Diplura, Pauropoda, and Symphyla

(Wallwork 1976). While our understanding of microarthropod ecology is still in its infancy,

we know that they can play a significant role in accelerating plant residue decomposition

through their interactions with the microflora (Seastedt 1984; Moore and Walter 1988;

Coleman et al. 2004). They are ‘‘litter transformers’’ fragmenting decomposing litter and

improving its availability to microbes (Wardle 2002). Fecal pellets of the particle-feeding

microarthropods, Collembola and the acarine suborder Oribatida (also called Cryptostig-

mata), have a greater surface-to-volume ratio than the original leaf litter and can lead

to greater decomposition per unit time (Coleman et al. 2004). The flow of energy and

nutrients through the soil also may be accelerated by microarthropods grazing on microflora,

causing increased rates of microbial biomass turnover. The importance of microarthropods

to litter breakdown rates varies with litter quality and is higher on litter of high C:N ratio

(low quality) (Coleman et al. 2004). Collembola and Oribatida (which include Astigmata

(Norton 1998)) are predominantly saprophages and mycophages, but some Oribatida show

opportunistic predation on nematodes and other microfauna, and scavenging on small dead

arthropods. The acarine suborders Prostigmata and Mesostigmata are mainly predatory,

but some Prostigmata and Mesostigmata (Uropodina) are mycophages (Wallwork 1976;

Norton 1985a).