Comparative Phytochemical Diversity Across Urban and Rural Plant Communities

Thesis Abstract

Urbanization alters plant communities and mediates phytochemical profiles, with potential implications for ecosystem services, human health, and biodiversity conservation. This study investigates how phytochemical diversity differs between urban and rural plant communities and explores the environmental drivers shaping these patterns, addressing the problem of how urbanization modulates secondary metabolite diversity and its functional consequences. The aim is to quantify and compare the diversity and composition of phytochemicals across urban–rural gradients and to identify abiotic and biotic factors associated with observed variation. Specific objectives include (i) cataloguing leaf, stem, and fruit phytochemical profiles using untargeted metabolomics; (ii) comparing richness, evenness, and beta-diversity of phytochemicals between urban and rural sites; (iii) assessing relationships between phytochemical diversity and environmental variables (soil nutrients, pollution indices, light intensity, temperature, rainfall) and plant traits (degree of domestication, phenology); (iv) testing whether anthropogenic disturbance mediates phytochemical variability through stress-related pathways; and (v) evaluating potential implications for pollinator interactions and human use of plant-derived compounds. A cross-sectional, observational design was employed across 24 sites distributed along an urban–rural transect in a temperate region. The population comprises perennial woody and herbaceous species commonly found in urban green spaces and adjacent rural habitats. A stratified sampling scheme selected 12 urban and 12 rural plots, with 15–20 vascular plant individuals per plot, yielding a minimum of 360 samples. Data collection utilized (i) untargeted metabolomic profiling of foliar and reproductive tissues via liquid chromatography–mass spectrometry (LC-MS/MS) to generate comprehensive phytochemical fingerprints, (ii) high-performance liquid chromatography (HPLC) for targeted phenolics and alkaloids quantification, and (iii) environmental assessments including soil pH, organic matter, macro- and micronutrients, heavy-metal concentrations, air and soil pollution indicators, ambient temperature, and light intensity. Botanical trait data were recorded for each sampled species (growth form, domestication status, phenology). Instrument validity was supported through calibration curves, internal standards, and duplicate injections for metabolomics, while plant identification was verified with a regional flora reference and DNA barcoding for ambiguous specimens. Data analysis followed a multi-tiered approach. First, metabolomic data were processed to generate presence–absence and intensity matrices, followed by alpha diversity metrics (richness, Shannon diversity) and beta diversity analyses (Bray–Curtis dissimilarity) to compare urban and rural communities. Multivariate ordination (principal coordinates analysis and canonical correspondence analysis) examined associations between phytochemical profiles and environmental variables. Generalized linear mixed models (GLMMs) tested the effects of urbanization level, pollution indices, and soil properties on phytochemical diversity, with plot and species as random effects. Structural equation modeling (SEM) assessed direct and indirect pathways linking urban stressors to phytochemical expression via plant stress responses and resource availability. Regression analyses evaluated links between phytochemical diversity and pollinator visitation rates, using standardized pollination surveys as supplementary data. Theoretical grounding integrates the Biophilic Urbanism framework and the Stress-Induced Metabolite Production theory, with empirical interpretation anchored in Optimal Foraging Theory regarding pollinator-mediated selection on chemical traits. Expected findings include higher social-ecological stress in urban plants driving elevated production of certain defensive or stress-responsive metabolites, but potentially reduced overall phytochemical richness due to species turnover and homogenization. It is anticipated that rural sites will exhibit greater metabolomic richness and more diverse compound classes, driven by greater plant diversity, less pollution, and stable microclimates. Key environmental drivers are predicted to be soil nutrient status, heavy-metal load, and light regime, with significant associations between phytochemical diversity and disturbance indices. The study will contribute to knowledge by clarifying how urbanization reshapes biochemical diversity, informing conservation of phytochemical resources, and guiding urban planning for biodiversity and ecosystem service outcomes. The results are expected to support a nuanced understanding that urban environments filter phytochemical diversity through stress-mediated production and species compositional shifts, with implications for pollinator interactions, ethnobotanical value, and pharmaceutical metabolite pools. Recommendations include enhancing habitat heterogeneity in urban landscapes to preserve phytochemical diversity, integrating phytochemical monitoring into urban ecosystem assessments, and promoting green infrastructure that mitigates stressors while sustaining plant biochemical value.