Multivariate edaphic gradients are associated with phytochemical quality variation in Atractylodes chinensis across northern China.

Environmental heterogeneity is widely invoked to explain geographic variation in medicinal plant quality. However, inference based on numerous intercorrelated soil variables can be unstable when individual correlations are interpreted separately. In this study, 42 rhizome-soil paired samples of Atractylodes chinensis were purposively selected across northern China to capture phytochemical variation and associated environmental data. The dataset included 32 cultivated samples and 10 wild reference samples; within Liaoning Province, the sampling set contained 25 cultivated samples and seven wild reference samples from corresponding production and distribution areas. Seven targeted phytochemical markers were quantified by HPLC, and 13 soil physicochemical variables were measured. Principal component analysis (PCA) was conducted separately on phytochemical and soil datasets. Using the Kaiser criterion (eigenvalue >1), six soil principal components (PCs) and two chemical PCs were retained, and all 12 cross-space PC combinations were tested with BH-FDR correction. Chemical PC1 and PC2 explained 37.68% and 23.22% of the total variance in phytochemical profiles, respectively. Soil PC1 and PC2 were not significantly associated with chemical PC1 (r=0.019, P = 0.906 and r=0.249, P = 0.112, respectively), whereas soil PC3 was significantly associated with chemical PC1 (Pearson r=0.465, P = 0.0019, q=0.0229; Spearman r=0.459, P = 0.0022; R 2=0.216; non-parametric bootstrap 95% CI: 0.24-0.66). This association remained significant in cultivated samples (n=32, r=0.538, P = 0.0015), Liaoning samples (n=32, r=0.570, P = 0.00066), and the 25 Liaoning cultivated samples (r=0.630, P = 0.00074), while no significant association was observed in the small wild subset (n=10, r=0.196, P = 0.587). A sensitivity analysis controlling for four retained climate PCs plus altitude yielded a similar partial association across the full dataset (partial r=0.484, P = 0.0024). This study identifies a reproducible multivariate association between soil properties and phytochemical profiles in cultivated A. chinensis. Nevertheless, purposive sampling, unknown genotype information, and the observational design preclude causal attribution to any individual soil factor.