Original Contribution to the Theory of Drought Adaptation Mechanisms in Nigerian Dryland Plant Species: Integrating Morphological, Physiological, and Molecular Evidence

Dryland plants of Northern Nigeria have evolved diverse and poorly characterised strategies for surviving and thriving under extreme water deficit, and a comprehensive theoretical framework integrating morphological, physiological, and molecular adaptation mechanisms for this flora represents a significant original contribution to plant stress biology. This study develops an integrated theoretical framework for drought adaptation in Nigerian dryland plant species and tests its predictions using a comparative approach across 24 species representing key functional types in the Sahel, Sudan savanna, and semi-arid zones of Borno, Yobe, Sokoto, and Katsina States. The theoretical framework proposes a Drought Adaptive Strategy Spectrum for dryland plants, defined by two orthogonal axes representing water use efficiency (conservative versus profligate) and drought recovery capacity (fast versus slow), generating four quadrant strategy types: desiccation tolerators, drought avoiders, efficient survivors, and resource opportunists. For each of the 24 study species, the following were measured: morphological traits (leaf rolling capacity, stomatal density, cuticular wax thickness, root-to-shoot ratio), physiological parameters (photosynthetic water use efficiency by carbon isotope discrimination, osmotic adjustment capacity, relative water content at zero turgor, and electrolyte leakage under stress), and transcriptomic responses (RNA-Seq under imposed progressive drought) at the University of Maiduguri Research Laboratory. Multivariate trait syndrome analysis correctly classified 92% of species into the four framework strategy quadrants. Transcriptomic analysis revealed that the desiccation tolerator group uniquely upregulated Group 3 late embryogenesis abundant protein genes, a molecular signature absent from the other three groups. An original Drought Adaptive Syndrome Index is derived from the multivariate trait analysis for rapid field assessment of species drought strategies. The study makes an original integrative contribution to the mechanistic understanding of drought adaptation in the West African dryland flora.

Keywords: drought adaptation, dryland plants, Sahel, desiccation tolerance, transcriptomics