Abstract:

Aims Interspecific interactions are a key determinant of wetland plant community assembly. As plant traits vary in different life history stages, the form, intensity and mechanisms of interspecific interactions may change with the ontogenetic process of plants. Seed germination is vital for plant life cycle and determines, to some extent, population distribution and community structure. In field sites, various seeds often appear in the same place, which makes the germination process affected by neighbouring conspecific or heterospecific seeds. Although some previous studies have discussed plant-to-seed and seed-to-seed interactions, the intensity of intra- and interspecific interactions during seed germination and the factors influencing these interactions are not well understood.
Methods We investigated the effects of density (80 seeds per dish, 160 seeds per dish) and seed proportion (monoculture, 3:1 mixture, 2:2 mixture, 1:3 mixture) on the germination rate and mean germination time of Spartina alterniflora, Scirpus × mariqueter and Phragmites australis seeds using petri dish experiments. In addition, the intensity of intra- and interspecific interactions under different species combinations was assessed by the relative neighbour effect (RNE) index.
Important findings The germination rates of Spartina alterniflora, Scirpus × mariqueter and Phragmites australis seeds increased at higher densities. When mixed with Spartina alterniflora seeds, the mean germination time of Phragmites australis seeds under the lowest proportion (25%) treatment was significantly longer compared to the other treatments. No competitive hierarchy was found among the seeds of these three plants, and there appeared to be intransitive competition. During seed germination, Scirpus × mariqueter had competitive dominance over Spartina alterniflora, and the latter was more competitive than Phragmites australis, which in turn, dominated Scirpus × mariqueter. Considering the complexity of intra- and interspecific seed-to-seed interactions in natural ecosystems, directly extrapolating the results from laboratory experiments to field environment may have constraints. Hence, further studies are needed to investigate the contribution of vegetative and sexual reproduction during regeneration stages via field surveys and manipulative experiments to improve our understanding of the assembly mechanisms of salt marsh plant communities.

Key words: Spartina alterniflora, Scirpus × mariqueter, Phragmites australis, density, intraspecific interaction, interspecific interaction, salt marsh, intransitive competition