Trophic ecology of mesostigmatan and oribatid mites in harvested and control coniferous and deciduous stands of the boreal mixedwood forest determined using 15N stable isotopes

Abstract

In boreal forest ecosystems, thick forest floors are a key habitat for microorganisms, micro- and mesofauna that drive soil biochemical processes. While they are the least abundant of soil mesofauna, mesostigmatan mites play a central role in soils by regulating population dynamics of other meso- and microfauna and by affecting nitrogen mineralization rates. The most abundant and diverse oribatid mites are especially important for decomposition processes in boreal forests. In this study, we evaluated the trophic ecology of mesostigmatan and oribatid mites from Canadian boreal forests by using body δ15N signatures as indicators of their trophic position. We extracted mites from the forest floors of control and clearcut stands from coniferous and deciduous stands dominated by white spruce (Picea glauca (Moench) Voss), and trembling aspen (Populus tremuloides Michx.), respectively. The mite values spanned 10.2 δ units in 15N, and were enriched by at least 1.2‰ compared to forest floor (baseline) values. When compiled to known eating habits from published feeding experiments, isotopic values placed the mites in three main trophic guilds, including detritivorous, omnivorous (overlapping with predators), and predator mites. Isotopic nitrogen fractionation within the mites did not seem to be affected by their habitat (spruce vs. aspen), or clearcutting practices. Instead, in this boreal forest environment, the well-defined degree of isotopic fractionation within the food web may be solely dependent on the mite feeding relationships.