Long term Spartina alterniflora invasion simplified soil seed bank and regenerated community in a coastal marsh wetland

The coastal wetland is easily invaded by alien species due to its location in the land and sea transitional area. As a potential driving regeneration force, the soil seed bank is vital to community restoration and species diversity protection. To reveal the long-term <em>S</em>. <em>alterniflora</em> invasion impact on the soil seed banks and regenerated communities, we investigated the seed banks under the different vegetation types (<em>S</em>. <em>alterniflora</em>, <em>Phragmites</em> <em>australis</em>, <em>Scirpus</em> <em>mariquete</em>, ruderal and unvegetated site) and soil depths (0–5 cm and 5–10 cm) in the Chongming island coastal salt marsh wetland. The results showed that the soil seed bank richness and species density under different vegetation types were higher than aboveground vegetation, and those of 0–5 cm seed banks were higher than 5–10 cm, except for the unvegetated site. The species richness and the <em>S</em>. <em>alterniflora</em> seed proportion in the seed banks under the <em>S</em>. <em>alterniflora</em> communities (S.AS) were lower and larger, respectively, than other sites. The species composition between S.AS and the aboveground communities showed high similarity with aggregation phylogenetic structures in two soil depths. The seed bank variations at 0–5 cm and 5–10 cm depths were interpreted 3.03% and 2.25% by aboveground communities, while 4.92% and 5.55% were interpreted by soil microbial biomass. The SEM model explained 98.1% and 91.8% of the seed banks' richness at the 0–5 cm depth and 5–10 cm depth, respectively, and explained 98.8% and 46.1% of the seed banks' species density at the 0–5 cm depth and 5–10 cm depth, respectively. The aboveground vegetation biomass and abundance directly affected the 0–5 cm seed banks' richness and species density, while its height and biomass only affected the 5–10 cm seed banks' species density. The microbial biomass of the 0-10 cm soil depth indirectly affected the richness and species density of the 0-5 cm seed bank, and only affected the richness of the 5-10cm seed bank. Soil physical and chemical properties only indirectly affected the 0–5 cm seed banks' species density. The results provided a reference for the ecological evaluation of the impacts of <em>S</em>. <em>alterniflora</em> invasion into the coastal salt marsh wetland of eastern China and guidance for the protection and restoration of the native plant communities. <br>

滨海湿地地处海陆过渡带，极易遭受外来物种入侵。土壤种子库（soil seed bank）作为潜在的自然更新动力，对群落恢复与物种多样性保护至关重要。为揭示互花米草（S. alterniflora）长期入侵对土壤种子库及更新群落的影响，本研究在崇明岛滨海盐沼湿地中，针对不同植被类型（互花米草、芦苇（Phragmites australis）、海三棱藨草（Scirpus mariquete）、杂草地以及无植被样地）与土壤深度（0–5 cm、5–10 cm）下的土壤种子库展开调查。研究结果显示，除无植被样地外，不同植被类型下的土壤种子库物种丰富度与物种密度均高于地上植被，且0–5 cm土层的土壤种子库相关指标高于5–10 cm土层。互花米草群落（S.AS）下的土壤种子库中，物种丰富度更低，而互花米草种子占比则高于其他样地。在两个土壤深度中，互花米草群落样地的土壤种子库与地上群落的物种组成相似度较高，且呈现聚集型系统发育结构。0–5 cm与5–10 cm土层的土壤种子库变异分别有3.03%与2.25%可由地上群落解释，而土壤微生物量（soil microbial biomass）的解释度分别为4.92%与5.55%。结构方程模型（SEM）分别解释了0–5 cm与5–10 cm土层土壤种子库物种丰富度的98.1%与91.8%变异，同时解释了0–5 cm与5–10 cm土层土壤种子库物种密度的98.8%与46.1%变异。地上植被生物量与多度直接影响0–5 cm土层土壤种子库的物种丰富度与物种密度，而植株高度与生物量仅对5–10 cm土层土壤种子库的物种密度存在影响。0–10 cm土层的土壤微生物量可间接影响0–5 cm土层土壤种子库的物种丰富度与物种密度，且仅对5–10 cm土层土壤种子库的物种丰富度存在影响。土壤理化性质仅间接影响0–5 cm土层土壤种子库的物种密度。本研究结果可为我国华东地区滨海盐沼湿地的互花米草入侵生态评估提供参考，同时为本土植物群落的保护与修复提供指导。