Feeding by the Oribatid Mite Scheloribates Alters Microbial Activity and Carbon Cycling

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Kyle Wickings
Stuart Grandy

Oribatid mites are among the most diverse soil mesofauna, and they possess a variety of metabolic and morphological feeding adaptations. Unfortunately, our understanding of the mechanisms by which oribatids may influence decomposition dynamics is incomplete. A microcosm experiment was conducted in which corn and oak leaf litter were incubated in the presence and absence of actively feeding oribatid mites Scheloribates sp. Our objective was to quantify the effects of Scheloribates sp. on microbial activity and carbon cycling within litter. Microbial activity was assessed by measuring C mineralization and microbial enzyme activity over a 3 month period. Respiration rates were measured using infrared gas analysis at three-day intervals and the activity of seven microbial extracellular enzymes was assessed weekly to bi-weekly using fluorometric and spectrophotometric techniques. Carbon dynamics were assessed by comparing the molecular chemical composition of the feces of Scheloribates sp. with that of the original litter using pyrolysis-gas chromatography/mass spectroscopy (py-GC/MS). Carbon mineralization rates increased slightly in the presence of an actively feeding mite population after one month of incubation. Similarly, the activity of many extracellular enzymes, including beta-glucosidase, chitinase, phenol oxidase and urease, was consistently higher in the presence of Scheloribates sp. than in their absence after 60 days. While the chemical composition of feces was similar to that of the original detritus, differences existed in the relative abundance of many compounds. This suggests that Scheloribates sp. may be feeding selectively on specific microbial and plant-based compounds within the detritus and that their ability to assimilate some compounds more efficiently than others results in the excretion of organic matter with a unique chemical structure. Our experiment demonstrates that Scheloribates sp. can influence carbon cycling indirectly by increasing the activity of microbial extracellular enzymes and directly by altering the molecular chemistry of decomposing organic matter through detritus feeding. Past work shows that many soil mesofauna can alter soil microbial and chemical processes. Given that soil mesofauna differ in food preference and digestive capabilities, we predict other taxa to vary considerably in their effects on these processes in litter. This prediction will serve as the basis for future work in our lab.