Abstract
Purpose
Soil degradation through salinization and alkalinization is one of the most widespread abiotic stresses threatening the health and functions of wetlands in the world. However, the relationship of this degradation to vegetation change in salt-affected inland wetlands is not well understood.
Methods
We studied the structure, density, and richness of aboveground vegetation, and soil physicochemical properties in Carex and Phragmites-dominated wetlands along a soil saline-alkalinization gradient in the Songnen Plain, China. We also compared the seed bank responses of Carex- and Phragmites-dominated communities to saline-alkaline stress in a greenhouse study.
Results
Following a structural equation model (SEM), the soil salinity and alkalinity were related to a decrease in the density and richness of aboveground vegetation. These environments indirectly affected the aboveground vegetation by reducing soil nutrients as well as the species richness and seed density of soil seed banks. Greenhouse experiments found that soil seed banks of Carex communities were more sensitive to saline-alkaline stress than Phragmites communities, especially the sedge species. SEM linked pathways of soil degradation, seed bank change, and plant diversity decline.
Conclusions
Our study indicates that soil salinity and alkalinity, as a critical environmental filter, could drive the decline of native freshwater species, especially for certain keystone sedge species, in salt-affected wetlands. Limiting agricultural development and restoring flood pulses across landscapes is necessary to alleviate soil salinization, deliver seeds and maintain the region’s freshwater vegetation in salt-affected inland wetlands.