A field study on seed bank and its potential applications in vegetation restoration of a polluted urban river in China

摘要

As an important component of restorations of polluted and/or degraded rivers, vegetation recovery has become a research highlight in the last two decades. Seed bank have been used as the best tool to allow natural recolonization of indigenous plants probably occurring before the degradation of the water bodies. To illustrate the relationship between water pollution and distribution of seed bank and evaluate the potential application of seed bank in vegetation restoration of polluted rivers, an urban river, Nanfeihe River was selected as the investigation target. A total of 27 species from 17 families with dominant families of Poaceae (5 species) and Polygonaceae (4 species) were identified in 38 channel bed samples. The observed species included 4 aquatic, 7 wetland and 16 terrestrial species, which occupied 15%, 26% and 59% of the total species, respectively. The species richness at the 10 sampling sites varied from 7 to 19, and the seed densities varied from 804 to 1.48 x 10~4 seedlings m~(-2). Species richness and seed density in the river margin were significantly higher than those in the mid-channel (P< 0.05), and those in upper sediment layers were also higher than those in sub-layers. The species richness and Shannon Index of seed bank were significantly related to total nitrogen (TN) concentration in the sediment by Gauss regression (R~2 = 0.94, P< 0.001 and R~2 = 0.91, P< 0.001). Increasing TN concentrations in sediment eventually led to the decline of species richness and diversity. CCA ordination suggested that water depth and NH_4~+-N concentration in water column played an important role in shaping the pattern of seed bank in the river. Perhaps water pollution not only caused degradation or even disappearance of standing vegetations, but also influenced the storage and distribution of seed bank. In addition, nitrogen-loading gradient along the river was probably capable of determining the pattern of seed bank at certain extend. The quantitative relations between the pattern of seed bank and water pollution give us insight to evaluate the potential application of seed bank in vegetation recovery in polluted urban rivers, and it would also contribute to urban riverine management, diversity conservation and ecological assessment.