The oribatid mite Scheloribates moestus (Acari: Oribatida) alters litter chemistry and nutrient cycling during decomposition

It is widely accepted that microarthropods influence decomposition dynamics but we know relatively little about their effects on litter chemistry, extracellular enzyme activities, and other finer-scale decomposition processes. Further, few studies have investigated the role of individual microarthropod species in litter decomposition. The oribatid mite Scheloribates moestus Banks (Acari: Oribatida) is abundant in many U.S. ecosystems. We examined the potential effects of S. moestus on litter decomposition dynamics and chemical transformations, and whether these effects are influenced by variation in initial litter quality. We collected corn and oak litter from habitats with large populations of S. moestus and in microcosms with and without mites measured respiration rates, nitrogen availability, enzyme activities, and molecular-scale changes in litter chemistry. Mites stimulated extracellular enzyme activities, enhanced microbial respiration rates by 19% in corn litter and 17% in oak litter over 62 days, and increased water-extractable organic C and N. Mites decreased the relative abundance of polysaccharides in decomposing corn litter but had no effect on oak litter chemistry, suggesting that the effects of S. moestus on litter chemistry are constrained by initial litter quality. We also compared the chemistry of mite feces to unprocessed corn litter and found that feces had a higher relative abundance of polysaccharides and phenols and a lower relative abundance of lignin. Our study establishes that S. moestus substantially changes litter chemistry during decomposition, but specific effects vary with initial litter quality. These chemical transformations, coupled with other observed changes in decomposition rates and nutrient cycling, indicate that S. moestus could play a key role in soil C cycling dynamics.