Trophic niche but not abundance of Collembola and Oribatida changes with drought and farming system

Higher frequencies of summer droughts are predicted to change soil conditions in the future affecting soil fauna communities and their biotic interactions. In agroecosystems drought effects on soil biota may be modulated by different management practices that alter the availability of different food resources. Recent studies on the effect of drought on soil microarthropods focused on measures of abundance and diversity. We here additionally investigated shifts in trophic niches of Collembola and Oribatida as indicated by stable isotope analysis (C-13 and N-15). We simulated short-term summer drought by excluding 65% of the ambient precipitation in conventionally and organically managed winter wheat fields on the DOK trial in Switzerland. Stable isotope values suggest that plant litter and root exudates were the most important resources for Collembola (Isotoma caerulea, Isotomurus maculatus and Orchesella villosa) and older plant material and microorganisms for Oribatida (Scheloribates laevigatus and Tectocepheus sarekensis). Drought treatment and farming systems did not affect abundances of the studied species. However, isotope values of some species increased in organically managed fields indicating a higher proportion of microorganisms in their diet. Trophic niche size, a measure of both isotope values combined, decreased with drought and under organic farming in some species presumably due to favored use of plants as basal resource instead of algae and microorganisms. Overall, our results suggest that the flexible usage of resources may buffer effects of drought and management practices on the abundance of microarthropods in agricultural systems.

Automated summary

This study predicts that higher frequencies of summer droughts will change soil conditions in the future, thus affecting soil fauna communities and their interactions. The effects of drought on soil biota in agroecosystems can be influenced by different management practices that alter the availability of food resources. The study focuses on the effect of drought on soil microarthropods and their trophic niches, using stable isotope analysis. The results suggest that plant litter, root exudates, and older plant material are important resources for certain species of Collembola and Oribatida. Drought and farming systems did not affect the abundance of species, but some species showed increased isotope values in organically managed fields, indicating a higher proportion of microorganisms in their diet. Overall, the study suggests that the flexible usage of resources can buffer the effects of drought and management practices on microarthropods in agricultural systems.