Questions

Germination is the prerequisite of successful establishment in plant communities and is influenced by many factors. Therefore, seeds are under strong selective pressure to sense and integrate information about their environment and modulate germination based on them. In this study, we focus on interspecific seed-seed interactions under optimal and sub-optimal conditions to test three hypotheses: (H1) Dominant species’ seeds and emerging seedlings are most likely to be recognized and insert significant effect on the germination of common subordinate species; (H2) Taxonomically related species are expected to exert stronger influence than un-related species on the germination of neighbouring seeds; (H3) Facilitative interactions are more likely to occur under sub-optimal conditions (drought stress) in the seed-seed interactions.

Location

Semi-dry temperate grassland belonging to Festuco-Brometea class, Cluj-Napoca, Romania

Methods

We assessed the rate and speed of germination of three common subordinate Asteraceae species (target species) in a controlled germination experiment. The target species’ seeds were sown in combination with low and high densities of neighbour species: two dominant Poaceae species, two subordinate Asteraceae species and two subordinate Apiaceae species; under optimal or drought conditions.

Results

Under optimal water conditions, particularly the seeds of the two dominant Poaceae species affected the germination of target species. Under drought stress, almost all neighbouring species altered the germination of two of the target species, enhancing or reducing their germination rate. Facilitation in seed-seed interactions was proved to be species-specific rather than general under drought conditions.

Conclusions

We found evidence that the status in a plant community (dominant or subordinate), but not the taxonomic relatedness influences the outcome of seed-seed interactions during germination. Under drought stress, the persistent competitive effect of the dominant species might considerably hinder the recruitment of subordinate grassland species.

We assessed the rate and speed of germination of three common subordinate Asteraceae species (target species) in a controlled germination experiment. The target species’ seeds were sown in combination with low and high densities of neighbour species: two dominant Poaceae species, two subordinate Asteraceae species and two subordinate Apiaceae species; under optimal or drought conditions.