Coastal dunes are unique ecosystems distributed worldwide. They share coastline-to-inland abiotic stress gradients determining their plant´s spatial distribution and biological interactions. Ambrosia chamissonis and Ammophila arenaria dominate coastal dunes in Chile, but there is scarce ecological information about their interactions and spatial distribution. The aim of this study was to characterize the coexistence of these two species and to evaluate the effect of stress gradients on their spatial distribution and performance. The study was carried out in three coastal dunes of the Ñuble Region, Chile; two dunes in which each species dominates and one in which they coexist. In each dune, sampling sites were defined along study transects perpendicular to the coast, where both soil characteristics (pH, salinity, contents of water, organic matter, nitrogen, phosphorus, and potassium) and biological variables of each species (cover, height, water content, content of foliar macronutrients) were measured. Variation of each abiotic variable with the distance from the high tide level was correlated to determine environmental stress gradients. A Canonical Correspondence Analysis (CCA) was performed to determine soils characteristics that better explained changes in plant abundance. The Relative Interaction Intensity index was calculated from biological variables and compared intraspecifically to determine dominant interactions along the dunes. Our results showed two soil stress gradients (soil salinity and available potassium) which decreased inland and may define in part, the spatial distribution of the species, as shown by the CCA. Our results support the idea that dune plants do not always follow the stress gradient hypothesis suggesting a modification of the hypothesis.

沿海沙丘是分布在世界各地的独特生态系统。它们共享海岸线到内陆的非生物胁迫梯度，决定了植物的空间分布和生物相互作用。Ambrosia chamissonis和Ammophila arenararia在智利沿海沙丘中占主导地位，但有关它们相互作用和空间分布的生态信息很少。本研究的目的是表征这两个物种的共存，并评估应力梯度对其空间分布和性能的影响。这项研究是在智利努布尔地区的三个沿海沙丘进行的；两个沙丘中​​每种物种占主导地位，另一种沙丘则它们共存。在每个沙丘中，沿垂直于海岸的研究横断面定义了采样点，其中包括土壤特征（pH、盐度、水含量、有机质、氮、磷和钾）和每个物种的生物变量（覆盖度、高度、测量水分含量、叶面大量营养素的含量。每个非生物变量随距高潮位距离的变化相关，以确定环境压力梯度。进行典型对应分析（CCA）以确定更好地解释植物丰度变化的土壤特征。相对相互作用强度指数是根据生物变量计算的，并进行种内比较以确定沿沙丘的主要相互作用。我们的结果显示，两个土壤应力梯度（土壤盐度和速效钾）在内陆减少，并可能部分定义物种的空间分布，如 CCA 所示。我们的结果支持沙丘植物并不总是遵循应力梯度假设的观点，这表明对假设的修改。