Above- and belowground effects of non-native earthworms in tallgrass prairie.

Abstract:

Previous research has shown non-native earthworms can alter functions and structure of ecosystems across North America. These changes include alterations to soil dynamics, plant communities, microbial functional groups, and disruption of arbuscular mycorrhizal (AM) fungi. In tallgrass prairies of the southern Great Plains, both native and non-native earthworms occur together. Compared to previously earthworm-free regions, few studies have investigated effects of non-native earthworms in regions where native earthworms are currently present, with even fewer on earthworm invasions in tallgrass prairies.

We conducted combined field and growth-chamber mesocosm studies to assess potential effects of non-native earthworms on plants and plant-fungal symbioses in tallgrass prairies in north-central Oklahoma. In the field study, we assessed earthworm abundance and species composition, plant species composition and biomass, and intra-radical AM hyphal abundance and total soil microbial biomass.

Non-native and native earthworms were found in our study site, with 73 non-native (Aporrectodea spp.) and 451 native (Diplocardia spp.) individuals identified. Abundances of neither native nor non-native earthworms were significantly associated with percent vegetation cover, vegetation biomass and richness, or intra- or inter-radical AM fungal abundance. However, greater numbers of total earthworms (native and non-native combined) were inversely related to native vegetation cover and positively related to non-native vegetation cover. Our research suggests total abundance of earthworms, but not specific species groups, may influence vegetation composition in tallgrass prairies, potentially reducing cover of native plants and promoting abundance of non-native plants. Non-native earthworms (A. trapezoides) may have similar effects on tallgrass prairie ecosystems as native earthworms (Diplocardia spp.) because both occupy the same ecological niche (endogeic) and have similar feeding habits. However, as alterations in vegetation community link with earthworm abundances, widespread ecosystem effects may increase as non-native earthworm invasion continues. Thus, continued studies of earthworm effects in tallgrass prairies is crucial to monitor further changes of this endangered ecosystem.