Plant–Soil Feedback Does Not Contribute to the Competitive Outcome Between Invasive and Resident Native Species in a Species-Rich Grassland

Question

Native and invasive species interact simultaneously with each other and with their species-specific soil biota, yet the relative importance of native plant–soil feedback (PSF) on the outcome of competition between these species with different origins is poorly understood. Therefore, we studied the influence of native PSF on the performance of two invasive and two native target species in two situations: (1) when the species were grown alone, and (2) when the target species were grown in pairwise competitive setup with the native conditioning species. We also tested the importance of phylogenetic relatedness between target and conditioning species on the simultaneous effect of PSF and competition.

Location

Cluj-Napoca, Romania.

Methods

We used native species from a semi-dry grassland dominated by Brachypodium pinnatum and Festuca rupicola to study how their species-specific PSFs affect the performance of invasive (Solidago canadensis, Erigeron canadensis) and native (Centaurea jacea, Crepis foetida) Asteraceae species. In the first year, soil was conditioned by six native grassland species (three Asteraceae and three species from other families); while in the second year, we performed a pairwise competition experiment in pots between the four target and six native species in conditioned and control soils.

Results

We found that although the native species exerted a strong negative PSF on the performance of the target species, this effect mostly disappeared in the real presence of the native competitors. We also showed that the identity of native resident species is more important in determining PSF and competitive outcome than whether it is dominant or subordinate, or whether it is phylogenetically related to the target species.

Conclusions

We showed that PSF of native species may not influence the competitive outcome between invasive and resident native species, thus PSF does not significantly contribute to the invasion resistance of the studied grassland community.