Physiological and Phytochemical Responses of Vernonia Amygdalina, Moringa Oleifera and Ocimum Gratissimum to Waterlogging-Induced Hypoxia: A Comparative Review
Abstract
Climate change-associated with flooding and prolonged soil waterlogging reduce oxygen availability in the root zone and can disrupt root respiration, nutrient uptake, photosynthesis, and plant growth. This review examines the physiological and phytochemical responses of Vernonia amygdalina, Moringa oleifera, and Ocimum gratissimum to waterlogging-induced hypoxia, with emphasis on species-specific responses, the strength of available evidence, and current research gaps. Literature from PubMed, Scopus, ScienceDirect, Google Scholar, and FAO AGRIS, primarily covering publications from 2009 to 2026, was critically synthesized. Evidence from the three selected species was considered alongside studies from related species where direct evidence was unavailable. The available literature indicates that M. oleifera has comparatively more direct evidence on physiological responses to waterlogging, including reductions in growth and photosynthetic performance, whereas direct evidence for V. amygdalina and O. gratissimum remains limited. Although hypoxia and associated oxidative stress can alter secondary metabolism, the available evidence is insufficient to conclude that waterlogging consistently increases specific medicinally relevant compounds such as chlorogenic acid, eugenol, vernodalin, or quercetin derivatives in these species. The review therefore distinguishes experimentally demonstrated responses from responses inferred from related species and those that remain hypothetical and require experimental validation. The resilience–remedy continuum proposed in this review is presented as a conceptual framework for relating plant stress adaptation to possible changes in phytochemical composition, rather than as a validated physiological or pharmacological relationship. Future research should employ controlled waterlogging experiments, soil oxygen measurements, physiological monitoring, and quantitative chromatographic, transcriptomic, and metabolomic analyses to clarify species-specific responses