Comparative Analysis of Drought Tolerance in Mediterranean and Subtropical Shrubs

Thesis Abstract

This study addresses the escalating concerns over plant resilience to drought conditions associated with climate variability, focusing specifically on the comparative drought tolerance of Mediterranean and subtropical shrubs. As these ecosystems face increasing water stress, understanding species-specific adaptive responses becomes critical for conservation and sustainable landscape management. The primary aim of this research is to elucidate the physiological, anatomical, and biochemical traits that underpin drought tolerance in select shrub species endemic to Mediterranean and subtropical regions, with the overarching goal of identifying key differentiators that influence resilience. To achieve this, the study sets out three specific objectives (1) to quantify and compare physiological parameters such as stomatal conductance, chlorophyll fluorescence, and water-use efficiency under controlled drought simulations; (2) to analyze anatomical features including cuticle thickness, xylem vessel characteristics, and root system architecture; and (3) to assess biochemical responses, specifically the accumulation of osmolytes, antioxidant enzyme activities, and stress-related gene expression. Employing a comparative research design, the study utilizes a mixed-methods approach integrating quantitative physiological and biochemical measurements with qualitative anatomical assessments. The population comprises five representative shrub species from Mediterranean ecosystems—such as Cistus albidus, Arbutus unedo, and Laurus nobilis—and five from subtropical regions, including Leptospermum scoparium, Rhus cotinus, and Corokia cotoneaster. A total of 150 individual plants (15 per species) are randomly sampled across multiple locations to account for environmental variability. Experimental data are collected under controlled greenhouse conditions where plants are subjected to gradually imposed drought stress over a period of four weeks. Instruments such as porometers, chlorophyll fluorometers, and spectrophotometers are employed to measure physiological and biochemical parameters, while high-resolution microscopy and histological staining techniques are used for anatomical analyses. Data are analyzed using Analysis of Variance (ANOVA) to identify significant differences among species and regions, coupled with multivariate regression models to examine relationships between physiological, anatomical, and biochemical traits. Canonical Correspondence Analysis (CCA) further explores the interaction of environmental factors with plant responses. The study also incorporates the Defense Response Theory and the Hydraulic Safety Hypothesis as theoretical frameworks to interpret adaptive strategies at different biological levels. Expected findings include distinct patterns of drought resilience, where Mediterranean shrubs might rely more on physiological adjustments such as increased water-use efficiency and antioxidant activity, while subtropical species may demonstrate more extensive anatomical adaptations like thicker cuticles and reinforced xylem structures. These differences are anticipated to be statistically significant (p < 0.05) and to reveal convergent and divergent strategies across both regions. This research contributes to the existing body of knowledge by providing integrated insights into adaptive traits that confer drought tolerance, thereby informing conservation strategies and selecting resilient species for restoration projects under changing climate scenarios. The findings are expected to demonstrate that while physiological plasticity is crucial, anatomical fortification provides lasting resilience, thus emphasizing the need for region-specific management practices. The study concludes with targeted recommendations for the selection and genetic improvement of drought-tolerant shrub species, advocating for further research into the molecular mechanisms underlying observed adaptive traits. Additionally, the research underscores the importance of incorporating multi-level plant responses into predictive models of ecosystem resilience, offering a comprehensive framework for future studies on drought adaptation in shrublands globally.