Abstract:

Groundwater depth （GD） is a critical hydrological factor regulating desert-wetland ecosystems. This study focused on the Dunhuang West Lake National Nature Reserve in Gansu Province， investigating the driving effects of GD on the spatial heterogeneity of soil physicochemical properties， species diversity， and the soil moisture-species diversity trade-off relationships. The results showed that as GD increased from 1.07 m to 5.42 m， soil total carbon （STC）， total nitrogen （STN）， and soil moisture content （SMC） decreased significantly （P<0.001）， while total dissolved salts （TDS） and soil C/N ratio （STC/STN） increased， revealing significant gradient differentiation in soil properties. Species richness （SP） and diversity （H） declined by 84.3% and 78.6%， respectively， with vegetation succession shifting from Phragmites australis-dominated mesophytic herbs to drought-tolerant species dominated by Glycyrrhiza inflata and Alhagi camelorum.Redundancy analysis demonstrated that GD （R²=0.4287）， SMC （R²=0.4916）， and pH （R²=0.4716） drove community differentiation through moisture-salinity gradients. GD showed a significant positive correlation with Glycyrrhiza inflata （R²=0.5370）， while SMC and pH were positively associated with hygrophytes such as Scirpus pumilus and Inula caspica.Hierarchical partitioning analysis indicated that environmental factors collectively explained 37.8% of species distribution variance， with GD （20.21%）， STC/STN （19.76%）， and SMC （17.30%） as key drivers （all P<0.001）. A critical GD threshold of 3 m was identified for the soil moisture-species diversity trade-off： synergistic relationships occurred below this threshold， while trade-offs intensified above it. This study reveals that GD drives spatial variations in species distribution and soil properties through moisture-salinity gradients， and maintaining GD within 3 m can preserve herbaceous community ecosystem functions. This threshold provides a crucial hydrological benchmark for desert-wetland ecological restoration.

Key words: groundwater depth, species diversity, soil physicochemical properties, trade-off, desert-wetland ecosystem