Characteristics and regeneration potential of soil seed banks in green space of urban parks in Beijing

Objective As a potential plant community, soil seed bank represents the regeneration and succession potential of aboveground vegetation to some extent. To study the characteristics of soil seed banks and their response to aboveground vegetation and soil factors in urban park green spaces can provide theoretical basis for the construction of urban parks near nature.

Method Taking the green spaces of parks within the Sixth Ring Road of Beijing as the object, they were divided into four types: comprehensive park, country park, cultural heritage park, and community park. In 75 randomly selected parks, aboveground vegetation surveys were carried out by sampling methods and soil sampling was carried out by randomization methods, the soil seed bank was determined by greenhouse germination method, soil physical and chemical indexes were obtained by conventional method.

Result (1) There were 77 species in the soil seed banks of Beijing City Parks, belonging to 34 families and 74 genera. Most of them were herbs (97.5%), with the highest number of species in the Asteraceae (16 species). Density of soil seed bank ranged from 352 to 899 grain/m², with Asteraceae having the highest seed reserves, followed by Gramineae and Leguminosae. The species with the highest density was Digitaria sanguinalis (147.11 grain/m²), followed by Medicago sativa (128.40 grain/m²), Setaria viridis (122.67 grain/m²) and others. Annal and biennial herbs were dominant in the four types of urban parks. The relative abundance of perennial herbs in country parks was higher than that in other types of parks, and the density of their seed banks was significantly greater than that in other types of parks (P < 0.05). (2) The Shannon-Wiener diversity index of the soil seed banks in urban parks ranged from 1.04 to 1.46, the Simpson dominance index ranged from 0.53 to 0.62, the Patrick richness index ranged from 4.79 to 8.41, and the Pielou evenness index ranged from 0.74 to 0.84, with the species richness of seed banks of country parks significantly greater than that of other types of parks (P < 0.05). (3) Similarity coefficients (Sørensen index) and non-metric multidimensional scaling analysis indicated that the similarity coefficients of soil seed bank and aboveground vegetation among different types of parks were high, and the differences in community structure were not significant. The similarity between soil seed bank and aboveground vegetation in the four types of urban parks was low, with similarity coefficients ranging from 0.10 to 0.18, and there were significant differences in community composition between them. (4) The density of soil seed banks was significantly positively correlated with herb diversity index, herb species richness index, soil ammonium nitrogen, and non-capillary porosity (P < 0.05), and significantly negatively correlated with soil total nitrogen and nitrate nitrogen. The species richness index of soil seed banks was significantly positively correlated with soil total nitrogen and nitrate nitrogen, and significantly negatively correlated with herb diversity index and soil ammonium nitrogen. The soil seed bank evenness, dominance, and diversity indices were significantly positively correlated with shrub species richness index and negatively correlated with herb species richness index. Among them, the herb diversity index and shrub species richness index had a greater impact on the density and species diversity of soil seed bank in urban parks.

Conclusion The density of soil seed banks in urban parks and the similarity between the soil seed banks and its corresponding aboveground vegetation is low, and the seeds of herb plants are dominated. The density and species diversity of the seed banks are mainly influenced by the diversity index of aboveground herb plants and the richness index of aboveground shrub species. Therefore, the soil seed bank renewal potential of urban parks is low, and artificial promotion of woody vegetation renewal is the key to build a near-natural urban park.