Abstract: Ordination methods were used to arrange in turn the 19 plant species in wetlands of the Yellow River Delta under gradients of water table depth and soil salinity, and to classify them into three ecological species groups, i.e. low, medium, and high water table depth/soil salinity ecological species groups. Their niche breadths and niche overlaps under the two gradients were also analyzed. The results indicated that for the gradient of water table depth, the species in medium water table depth ecological species group, such as Phragmites australis and Suaeda salsa, occupied a broad niche breadth, and those in high water table depth ecological species group, such as Typha orientalis and Myriophyllum spicatum, occupied the narrowest niche breadth. For the gradient of soil salinity, the species in high soil salinity ecological species group, such as Suaeda salsa and Tamarix chinensis, occupied a broad niche breadth, while those belonging to the medium and low soil salinity ecological species groups occupied a narrow niche breadth. The niche overlaps changed regularly along the gradients of water table depth and soil salinity. In general, the niche overlaps between the plant species of the same ecological species groups were large, whilst those between the plant species of different ecological species groups were small. Niche differentiations of the plant species under the gradients of water table depth and soil salinity might promote species coexistence, and contribute to the explanation of plant zonation mechanisms in this Delta.

Key words: settlement morphology, commuting, urban transportation, energy consumption, greenhouse gases emission.