Environment Modification Mediates Seed-to-seed Interactions between Dominant Species in the Yangtze River Estuary

Plant community assembly is the central issue in community ecology. As plant traits differ in different life history stages, the form, intensity and mechanism of interspecific interactions may change with the ontogenetic process of plants. However, our understanding of interspecific interaction mechanisms during germination is still limited. Here, we conducted a laboratory germination experiment using 5 dominant species in Chongming Dongtan (Spartina alterniflora, Scirpus mariqueter, Phragmites australis, Suaeda glauca and Tripolium vulgare) to assess their germination performance in control (monoculture), allelopathy and mixture treatments. The results indicated that seeds could affect germination performance of neighbours through both allelopathy and microenvironment modification. Salinity of the solution in petri dishes after germination decreased in all treatments, and was negatively correlated with the number of total germinated seeds. Seed leachate of invasive Spartina alterniflora inhibited the germination of native Scirpus mariqueter and Phragmites australis, but not the two halophytes Suaeda glauca and Tripolium vulgare. The salt absorption by Spartina alterniflora seeds had the opposite effects compared with that of its seed leachate. On the other hand, seed leachate of native species promoted the germination of invasive Spartina alterniflora. The effect of microenvironment modification of Scirpus mariqueter and Phragmites australis was positive, whereas that of Suaeda glauca and Tripolium vulgare was neutral or negative. Considering seed-to-seed interactions is an important perspective to understand the underlying mechanisms of community dynamics, species diversity maintenance and invasion of alien species, and can improve the effectiveness in the management of invaded coastal wetlands.