Table1_Groundwater depth alters soil nutrient concentrations in different environments in an arid desert.docx

Soil nutrients are vital for plant growth and survival and present a crucial role in terrestrial function and productivity. However, little is known about the effect mechanism of groundwater table on soil nutrients in an arid desert ecological system. This study investigated the impacts of groundwater depth on the concentrations of soil organic carbon (C), available nitrogen (N), phosphorus (P), and potassium (K) at shallow groundwater depths (0.4, 0.8, 1.2, 1.8, and 2.2 m) and field deep groundwater depths (2.5, 4.5, and 11.0 m) in a desert-oasis ecotone in Central Asia in 2015 and 2016. Soil nitrate-N, inorganic-N, soil available P, and K concentrations were significantly affected by shallow and field deep groundwater. Groundwater depths did not alter soil ammonium-N concentration. Soil organic C concentration was influenced by field deep groundwater depth. Structural equation model showed that groundwater depth directly affected soil nitrate-N and K concentrations and indirectly altered the soil inorganic-N, soil organic C and available P concentrations in shallow groundwater. Moreover, groundwater depth directly influenced soil nitrate-N and soil organic C, available P and K concentrations and indirectly affected soil inorganic-N concentration in deep groundwater. Hence, groundwater depth should be considered one of the most critical environmental factors affecting soil nutrient variation in an arid desert. This study provides new insights into the soil nutrient variation under a declining groundwater depth in a hyper-arid ecosystem.

土壤养分对于植物生长与存活至关重要，同时在陆地生态系统功能与生产力中发挥着关键作用。然而，当前对于干旱荒漠生态系统中地下水位对土壤养分的作用机制仍所知有限。本研究于2015年和2016年，在中亚的荒漠绿洲过渡带，针对浅层（0.4、0.8、1.2、1.8和2.2 m）与野外实测深层（2.5、4.5和11.0 m）地下水埋深梯度，探究了其对土壤有机碳（C）、有效氮（N）、磷（P）及钾（K）浓度的影响。研究结果表明，土壤硝态氮、无机氮、有效磷与钾浓度均显著受浅层及深层地下水埋深的影响；地下水埋深并未对土壤铵态氮浓度产生显著作用；而土壤有机碳浓度则受深层地下水埋深的调控。结构方程模型（Structural Equation Model）分析显示，在浅层地下水环境中，地下水埋深可直接影响土壤硝态氮与钾浓度，并间接改变土壤无机氮、有机碳及有效磷浓度。此外，在深层地下水环境中，地下水埋深可直接影响土壤硝态氮、有机碳、有效磷与钾浓度，并间接影响土壤无机氮浓度。综上，地下水埋深应被视为影响干旱荒漠地区土壤养分变异的核心环境因素之一。本研究为超干旱生态系统中地下水埋深下降背景下的土壤养分变异研究提供了全新的视角。