Mechanisms of Seed-To-Seed Interactions between Dominant Species in the Yangtze River Estuary under Saline Condition

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 five 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 neighbors through both allelopathy and salinity modification. Salinity of the solution in Petri dishes after seed germination decreased significantly in most species combinations in competition treatment, and was negatively correlated with the number of total germinated seeds. Seed leachate of invasive Spartina alterniflora significantly accelerated the germination of two native halophytes Suaeda glauca and Tripolium vulgare, but not Scirpus mariqueter and Phragmites australis. The salt absorption by Spartina alterniflora seeds had inconsistent effects compared with that of its seed leachate. On the other hand, seed leachate of native Scirpus mariqueter and Phragmites australis significantly slowed down the germination of invasive Spartina alterniflora. The effect of salinity modification of Scirpus mariqueter on Spartina alterniflora was positive, whereas that of other species was neutral. 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.