Exploring Soil–Microbe Associations with Grapevine Nutrition in Tasmanian Pinot Noir Vineyards

(1) Background: Soil nutrient availability in vineyards is shaped by physicochemical and biological processes. However, how baseline edaphic differences are related to soil microbial functional genes and plant elemental composition under biodynamic management remains unclear; (2) Methods: Two biodynamically managed Pinot Noir (Vitis vinifera L.) vineyard sites in Tasmania, hereafter referred to as site 1 (S1) and site 2 (S2), were compared at fruit set, veraison, and ripening. Soil physicochemical properties were measured, soil, leaf, and grape berry elemental compositions were assessed by X-ray fluorescence, and soil microbial taxonomic marker genes and soil microbial functional genes were quantified by qPCR. Because the dataset comprised only six site-by-stage composite samples without independent field-level biological replication, multivariate analyses and partial least squares path modeling were used as exploratory tools; (3) Results: The two sites showed distinct baseline soil physicochemical properties. Soil microbial functional genes varied across sites and phenological stages, with several nitrogen (N)-cycling genes showing higher values at S1 and amoA increasing toward ripening at both sites. AMG, defined here as an arbuscular mycorrhizal fungal (AMF)-related marker, also increased toward ripening and was interpreted separately from the N-cycling genes. Soil elements mainly reflected site-related differences, whereas leaf and berry elements showed clearer variation across phenological stages. The exploratory path model, based on this limited composite dataset, summarized sequential associations among soil physicochemical properties, microbial functional genes, leaf elements, and berry elements, as well as a direct association between soil physicochemical properties and berry elemental composition; (4) Conclusions: These findings describe exploratory soil–microbe–plant association patterns under biodynamic management and should not be interpreted as statistically inferential or causal evidence.