Metabarcoding mites: Three years of elevated CO2 has no effect on oribatid assemblages in a Eucalyptus woodland

Abstract

Elevated atmospheric carbon dioxide concentrations (eCO2) are known to significantly impact aboveground vegetation, with cascading effects on belowground systems. However, the effects of altered biogeochemical and hydrological cycles on belowground faunal assemblages remain unclear. Oribatid mites are abundant and hyperdiverse litter decomposers, with the potential to act as bioindicators of ecosystem disturbance. Here, we assessed oribatid mite assemblages under ambient and eCO2 (ambient +150 ppm) at the Eucalyptus Free-Air CO2 Enrichment (EucFACE) facility using high-throughput sequencing of the mitochondrial cytochrome oxidase 1 (COI) gene. Our aims were to i) quantify the effect of eCO2 on mite abundance and diversity, and ii) evaluate metabarcoding as a reliable approach for the rapid assessment of oribatid mite assemblages. Three years of eCO2 exposure resulted in lower soil pH but had no significant impact on mite abundances or oribatid mite assemblage structure. Instead, mite densities were found to correlate negatively with soil NH4+, while oribatid species richness using both morphological and metabarcoding datasets were positively correlated with total soil nitrogen content. Additionally, metabarcoding showed that oribatid mite assemblage structure was correlated with total soil carbon and nitrogen content, and soil pH. However, dissimilarity matrices based on the two approaches were not correlated, indicating that metabarcoding can be used as a proxy for shifts in assemblage structure but cannot be directly compared with morphological datasets. This study demonstrates how metabarcoding can rapidly assess belowground assemblages, providing a useful monitoring tool under current and future climate scenarios.