The spatial overlapping regulated by nitrogen promotes the Spartina alterniflora potential invasion in coastal wetlands

Clarifying the interaction between aboveground plant communities and soil seed banks is conducive to predicting community potential regeneration direction. However, the spatial structure of invasive clonal plants should be reasonably quantified. We assumed that the selection effect of Spartina alterniflora community spatial structure on soil seed bank species composition would affect the seed reproduction invasion intensity. Taking the native species of Phragmites australis in Dongtan wetland as a reference, we explored the nitrogen regulation on the soil seed bank formation process after S. alterniflora became the dominant species. The results showed that S. alterniflora growth tended to be stable in summer and autumn, and its height change trend and peak height under different coverage were relatively consistent. The seasonal variation of P. australis height was opposite to that of S. alterniflora. At community mature stage in the autumn, the dominance index of S. alterniflora and P. australis showed a downward trend from low to high aboveground coverage after the soil seed bank germination, and the dominance index of S. alterniflora was higher than that of P. australis. The overlapping resistance structure of S. alterniflora community was synergistically affected by soil ammonium nitrogen, leaf total nitrogen and soil microbial biomass nitrogen, and the effect of structure on the soil seed bank formation under different soil depth showed an opposite trend. Our results suggested that the overlapping complementarity between S. alterniflora would play a positive regulatory role between functional trait plasticity and sexual reproduction advantage.