Comparative Phytochemical and Antioxidant Profiling Across Urban Green Spaces

Thesis Abstract

Urban green spaces (UGS) are increasingly recognized as reservoirs of bioactive compounds with potential benefits to human health and urban resilience, yet comparative phytochemical and antioxidant profiles across different UGS types remain underexplored. This study addresses the gap by examining how plant-based phytochemicals and antioxidant capacity vary among urban parks, green corridors, and community gardens, and how environmental stressors associated with urbanization modulate these profiles. The aim is to quantify and compare phytochemical diversity and antioxidant activity across UGS categories and to identify abiotic drivers influencing these patterns. Specific objectives are (1) to profile key phytochemical classes (phenolics, flavonoids, terpenoids) in representative plant species common to urban ecosystems; (2) to quantify total phenolic content (TPC), total flavonoid content (TFC), and antioxidant capacity using ABTS, DPPH, and FRAP assays; (3) to assess inter-site and inter-species variation using multivariate analyses; (4) to evaluate associations between environmental variables (soil pH, heavy metal concentrations, light intensity, and ambient air quality indices) and phytochemical/antioxidant metrics; and (5) to integrate findings within a theoretical framework to propose management practices that optimize phytochemical richness in UGS. The study adopts a cross-sectional comparative design conducted in a mid-sized metropolitan region during the peak growing season. Population includes vascular plant species routinely sampled in three UGS typologies municipal parks (n=12 sites), green corridors (n=12 sites), and community gardens (n=12 sites). A stratified random sampling approach yields 36 sites, with three dominant plant species per site selected for analysis, totaling 108 plant-species samples. Data collection involves (i) field measurements of environmental variables (light intensity using quantum sensors, soil samples for pH, EC, and heavy metal analysis by ICP-MS, and local air quality indices from fixed monitoring stations), (ii) plant tissue collection (young leaves and inflorescences) following standardized botanical protocols, and (iii) laboratory assays for phytochemical and antioxidant analyses. Phytochemical profiling emphasizes targeted quantification of total phenolics (via Folin–Ciocalteu method), total flavonoids (aluminum chloride colorimetric method), and secondary metabolite fingerprinting through high-performance liquid chromatography coupled with diode-array detection (HPLC-DAD) and liquid chromatography–mass spectrometry (LC-MS) for compound annotation. Antioxidant capacity is assessed with ABTS, DPPH, and FRAP assays to capture electron transfer and radical scavenging activities. Methodological rigor is ensured through calibration with standard references (gallic acid, quercetin, Trolox) and validation of instrument performance. Statistical analyses combine descriptive, univariate, and multivariate techniques. Descriptive statistics summarize phytochemical contents and antioxidant metrics by UGS type and species. Inferential analyses employ mixed-effects ANOVA to test for differences across UGS categories while accounting for plant species as random effects, and MANOVA to evaluate multivariate phytochemical profiles. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) elucidate relationships among sites, species, and measured phytochemical attributes. Redundancy analysis (RDA) investigates associations between environmental drivers (soil and air variables) and phytochemical/antioxidant outputs. Regression modelling (generalized linear models) explores the predictive power of abiotic factors on antioxidant capacity, with model selection guided by Akaike Information Criterion (AIC). Theoretical grounding integrates the Stress-Gradient Hypothesis and the Optimal Defense Theory to interpret urban environmental effects on secondary metabolite accumulation. Expected findings anticipate higher phenolic and flavonoid contents and greater antioxidant activity in plant tissues from community gardens relative to parks and green corridors, potentially driven by heterogeneous microhabitats and localized stressors that stimulate secondary metabolism. Species-specific responses are anticipated, with tolerant native species showing pronounced phytochemical accumulation under elevated light and soil contaminants. The study will illuminate the extent to which UGS typology shapes phytochemical diversity and antioxidant potential, and identify environmental covariates that most strongly predict bioactive profiles. Contributions to knowledge include a cross-sectional evidentiary basis for urban botany that links habitat type, environmental determinants, and plant chemical defenses, informing urban biodiversity conservation, public health nutrition strategies, and green infrastructure planning. The main conclusion will emphasize that targeted enhancement of microhabitat heterogeneity and careful selection of species in urban designs can maximize phytochemical richness and antioxidant benefits. Recommendations include adopting mixed-species plantings with native varieties, improving soil remediation in high-exposure areas, and prioritizing maintenance practices that preserve plant biochemical diversity without compromising ecosystem services. Suggestions for future research propose longitudinal monitoring to capture seasonal dynamics and experimental manipulation of environmental stressors to establish causal links.