Phytochemical and Growth Patterns in Cistus albidus L.: Seasonal Impacts of Inoculation and Fertilization

Seasonal dynamics and cultivation practices jointly regulate plant growth and secondary metabolism, yet their relative contributions and modes of interaction remain insufficiently resolved in many medicinal species. In this study, the effects of organic fertilization and arbuscular mycorrhizal fungus (AMF) inoculation on vegetative development, flowering behaviour, and phytochemical profiles of Cistus albidus L. across one complete vegetative cycle under controlled cultivation conditions have been examined. Four treatment groups (control, fertilization, inoculation, and combined fertilization + inoculation) were evaluated with respect to growth parameters, reproductive output, total phenolic content (TPC), antioxidant capacity, and polyphenolic composition using UHPLC–MS. Across the vegetative cycle, seasonal progression emerged as the dominant regulator of both growth and metabolic traits, exerting strong control over leaf morphology, specific leaf area, flowering dynamics, and the temporal organisation of individual secondary metabolites. Fertilization primarily stabilised vegetative growth and reduced inter-individual variability, whereas AMF inoculation imposed consistent growth constraints, reduced reproductive output, and increased phenotypic and metabolic variability. Despite the absence of growth promotion typically associated with functional mycorrhizal symbiosis, inoculated plants exhibited elevated antioxidant capacity and increased concentrations of selected phenolic compounds, particularly during autumn. Phytochemical regulation was class-specific rather than uniform. Flavan-3-ols and flavonols displayed high seasonal plasticity and context-dependent responsiveness to inoculation, whereas phenolic acids, ellagitannins, and the secoiridoid glycoside were structured predominantly by harvest time and developmental stage. Total phenolic content and antioxidant capacity were only weakly coupled, reflecting opposing seasonal trajectories among individual compounds and highlighting the importance of matrix-level organisation rather than bulk metabolite accumulation. These results indicate, cultivation practices influenced C. albidus primarily by modulating growth regulation and developmental allocation, while secondary metabolism was reorganised selectively within a strong seasonal framework. This integrative response provides a conceptual basis for interpreting growth–defence–signalling trade-offs in medicinal plants under controlled cultivation.