黄河三角洲滨海湿地地下水位变化对土壤种子库特征的影响

地下水位是影响湿地生态系统结构和功能的重要环境因子之一,然而其如何影响滨海湿地土壤种子库特征尚不清楚。通过地下水位控制试验,研究黄河三角洲滨海非潮汐湿地地下水位梯度（-20、-60、-100 cm）下,土壤种子库密度、物种多样性等特征,并通过土壤化学指标与对应的土壤种子库特征之间的通径分析,探讨地下水位深度变化对土壤种子库特征的影响机理。研究发现,在该区域秋季采样的土壤种子库中,碱蓬和盐地碱蓬的种子数量最多;地下水位变化对土壤种子库密度无显著影响,但对土壤种子库的物种组成影响较大,随着地下水位深度增加,多年生草本植物种类呈增加趋势。整体上,随着地下水位深度增加,土壤种子库的Margalef丰富度指数和Shannon-Wiener多样性指数随之增大。主成分分析表明,土壤盐是影响黄河三角洲滨海湿地土壤种子库组成特征的主导因素,贡献率为69.482%,土壤养分为次要影响因素,贡献率为23.710%,进一步通径分析表明,土壤水溶性盐总量对种子库物种多样性起到限制作用,同时,有效磷浓度通过水溶性盐总量对Margalef指数和Shannon-Wiener指数表现为间接负作用,总磷浓度对种子库与地上植被相似性起到促进作用。研究表明,黄河三角洲滨海湿地地下水位深度变化,主要通过影响土壤水溶性盐总量,进而影响土壤种子库物种多样性。

Effects of groundwater level fluctuation on characteristics of soil seed banks in coastal wetlands of the Yellow River Delta

Soil seed banks are sources for the future regeneration of plants and play an important role in long-term population balance. Groundwater level is one of the dominant environmental factors that affects the structure and function of wetland ecosystem. While the effects and mechanisms of groundwater level on the characteristics of soil seed banks in coastal wetlands have received less attention. In order to study the effects of groundwater level on soil seed bank density, species diversity and similarity between seed banks and aboveground vegetation, a field control experiment for groundwater level was carried out following the gradients of -20 cm, -60 cm, and -100 cm in the coastal wetlands of the Yellow River Delta. The relationship between soil chemical properties and characteristics of the corresponding seed banks was analyzed by correlation analysis, principal component analysis and path analysis to explore how different groundwater levels affect the characteristics of the soil seed banks. The study showed that Suaeda glauca and Suaeda salsa had the largest number of seeds in the soil seed banks collected in autumn (both transient and persistent seed banks) in coastal saline wetland of the Yellow River Delta. The change of groundwater level had no significant effects on the density of soil seed banks, but it had significant effects on species composition. As the depth of groundwater level increased, the species number of perennial herbs were increasing. Overall, as the depth of groundwater level increased, Margalef index and Shannon-Wiener index of soil seed banks increased accordingly. A novelty finding is that the similarity (Sørensen index) between seed banks and above-ground vegetation increased as the groundwater level increased in 5-10 cm soil layer. Principal component analysis showed that soil salt including total water-soluble salt content and saline ions concentration was the dominant factors affecting soil seed bank characteristics with a contribution ratio of 69.482% and soil nutrients including total carbon, nitrogen and phosphorus concentration were the secondary factors with a contribution ratio of 23.710%. Path analysis showed that soil total water-soluble salt content had the greatest negative influence on Margalef index and Shannon-Wiener index of seed banks. While soil available phosphorus concentration showed indirectly negative effects through total water-soluble salt content on Margalef index and Shannon-Wiener index of seed banks. Total phosphorus concentration promotes the similarity between seed banks and the above-ground vegetation. Our results indicated that groundwater level fluctuation mainly affected species diversity of soil seed banks by changing the content of soil total water-soluble salt in coastal wetlands of the Yellow River Delta.