Responses of Plant Community Composition and Eco-Physiological Characteristics of Dominant Species to Different Soil Hydrologic Regimes in Alpine Marsh Wetlands on Qinghai–Tibetan Plateau, China

Abstract

Shifts in soil water content affect seasonal wetland plant communities worldwide, but little is known about the responses and influences of plant communities to soil water content on Qinghai–Tibetan Plateau. To determine the relationship between soil water content and plant community structure in seasonally wet alpine marshes, we investigated plant community structures at different soil water content amounts in the field station at sampling sites. We selected and determined eco-physiological characteristics of species belonging to three different functional types (sedges, grasses, forbs) exposed to the same soil water regimes as characteristics in field station and under experimental flooding conditions in controlled treatments on pots plants. The field investigation indicated that decreased soil moisture (from 57 to 43 % m3 m−3) during the growing season was significantly associated with reductions in aboveground biomass, average plant height, and species richness. A shift in dominant plant species within the communities from sedges and grasses to some forbs accompanied the decrease in soil moisture. The controlled treatments demonstrated that the sedge and grass species had higher net photosynthetic rates and higher instantaneous water-use efficiencies than the forb species in the studied communities. The results indicate that shifts in wetland plant community structure and function are the result of longer dry periods and more intense rainfall events. This positive feedback suggests that changes in plant community composition could intensify soil drought conditions in seasonally wet alpine marshes in the future.