Twig and Leaf Morphological Traits and Photosynthetic Physiological Characteristics of Periploca sepium in Response to Different Light Environments in Taohe Riparian Forests

Understanding the variations in twig and leaf morphologies and photosynthetic physiological characteristics of riparian forest plants in heterogeneous habitats is of great significance for revealing their phenotypic plasticity mechanisms and ecological adaptation strategies. In this study, the riparian forest plant <i>Periploca sepium</i> Bunge was selected as the research object. According to the canopy light environment experienced by the <i>P. sepium</i> population, three habitats were established: under-canopy, gap, and full-sun areas. We studied the twig and leaf morphological and photosynthetic characteristics of <i>P. sepium</i> under heterogeneous light environments, as well as the relationships between these two aspects. Plants in the under-canopy area developed long and thick twigs with few large leaves, coupled with high actual photosynthetic efficiency of photosystem II (Y(II)) and low non-photochemical quenching (NPQ), whereas those in the full-sun area exhibited the opposite covariation strategy. Significant correlations between twig and leaf morphologies and photosynthetic physiological characteristics were found across all habitats. The coordinated variations in twig and leaf morphologies and photosynthetic physiology of <i>P. sepium</i> embody a resource investment trade-off strategy that plants have evolved through long-term adaptation to heterogeneous light environments.