Raw data of the microarthropods and decomposition from: Effects of microarthropod density on soil fungal community composition in nutrient-poor ecosystems

Microarthropods such as mites (Acari) and springtails (Collembola) play a key role in the functioning of nutrient-poor ecosystems. They contribute to the comminution of organic matter and they are likely to affect the structure and function of soil microbial communities through grazing and by changing substrate availability. However, the precise effects of their interactions with microbiota remain poorly understood. In the present study, we conducted a mesocosm field experiment to determine the effects of soil microarthropod density on community composition of soil fungi. We manipulated microarthropod densities in 100 defaunated and soil-filled meshed mesocosms by inoculating half of the units with microarthropods (i.e. high density treatment), while the other half of the units only contained few specimens possibly hatching from recalcitrant eggs that survived defaunation (i.e. low density treatment). All mesocosms were then inserted in the top soil of a range of nutrient-poor grasslands and heathlands in Belgium for the duration of three months. The entire mesocosms were composed of mesh (30 µm mesh size) to allow for a rapid (re-)colonization by microbes from the surrounding soils, while migration of microarthropods in or out of the mesocosms was precluded. Litter bags (30 µm mesh size) containing two types of organic matter were also buried within each mesocosm, and organic matter mass loss over time was used as a proxy to assess effects of microarthropod density on microbe-regulated decomposition rates. We found that fungal community composition differed strongly between the two microarthropod density treatments, regardless of habitat type. The mesocosms with higher microarthropod densities were characterized by a higher number of fungal OTUs and a higher number of fungal indicator species associated to this treatment. Microarthropod density, however, did not affect microbe-regulated organic matter decomposition rates, nor did it affect relative abundances of putative fungal functional groups, thus suggesting considerable levels of fungal functional overlap.

Synthesis: The lack of measurable changes in organic matter decomposition or shifts in fungal functional group representation suggest that effects of microarthropods on the functioning of fungal communities may be lower than originally thought.

Methods
This dataset was collected during a three-month mesocosm experiment taking place in different nutrient-poor habitats (heathland, Nardus grassland, and restored grassland). It includes data on the number of microarthropods (mites and springtails) for three treatment levels i.e. low density, high density, and reference, and the decomposition outcomes for two litter types i.e. heather and cellulose. We verified whether the inoculated (treatment H) and control (treatment L) mesocosms indeed differed in microarthropod density, using a generalized linear model using Poisson regression or quasipoisson regression for over-dispersed data; sites 4 (grassland) and 10 (heathland) (7 samples each) were excluded from further data analysis due to errors in the inoculation processes. For the decomposition experiment we calculated weight loss after three months of the two incubated organic matter types, after which we  estimated decomposition rates using the first order decay constant (k).

The effects on fungal communities were also assessed by processing the sequencing data referenced as related works.