Interaction process and feedback mechanisms of hydrology -soil-vegetation systems in oasis wetland, northwest China

Wetlands play important roles in the ecological balance and sustainable development of arid oases. However, the interactions and feedback mechanisms in oasis hydrology–soil–vegetation systems are unclear. We conducted a 5-year field study in swamp, riparian, grassland, shrubland, and reclamation oasis wetlands to analyze the hydroclimatic processes, soil physicochemical properties, vegetation characteristics, and their interactions and feedback mechanisms in northwestern China. The precipitation was low (122.5±12.3 mm yr-1), and the differences among different wetland types were significant, with an average annual evapotranspiration of 598.2 to 654.5 mm yr-1, a groundwater depth of 85.4±5.3 to 130.1±14.8 mm), and a soil water content (SWC) of 0.26±0.03 to 0.39±0.09 v/v). Groundwater depth significantly affected  SWC, pH, EC, nutrients, ions, and microbial and vegetation diversity. The differences among wetlands were significant. Reclamation for agriculture significantly increased Cl-, CO32-, Mg2+, and K+, but significantly decreased SO42-, HCO3-, Ca2+, and Na+. The overall vegetation community contained 17 families, 40 genera, and 46 species, of which dicotyledons were dominant, accounting for 56.5% of total number. Path modeling showed that groundwater depth directly affected soil water content (88%), soil ion contents (56%), and nutrient contents (32%), thereby indirectly affecting soil microbe and vegetation diversity. SWC affected vegetation diversity more strongly than groundwater depth in the wetlands, resulting in differences of vegetation diversity (total effect size, 85.3%), with a direct effect of 62.9% and an indirect effect of 23.2%. Our results show that the interactions among hydroclimatic processes, soil physicochemical properties, and human activities affect species diversity and vegetation characteristics in oasis wetlands.