Understanding how growth and defense strategies of perennial plants change across developmental stages in response to elevated atmospheric CO2 is critical for predicting adaptive responses and ecological interactions under future climate scenarios. In this study, Aristolochia contorta, a perennial herb, was examined across age groups (1-, 2-, and 10-year-old plants), under ambient and elevated CO2 (540 ppm, simulating RCP 4.5). Growth traits, carbon-to-nitrogen (C/N) ratios, and concentrations of secondary metabolites in both above- and below-ground tissues were measured to evaluate developmental and environmental effects on plant physiology. Growth parameters, including plant height, total leaf area, stem thickness, and biomass increased with age, but were suppressed under elevated CO2 across all age groups. In 1- and 2-year-olds, the C/N ratio also decreased under elevated CO2, suggesting altered resource allocation during early developmental stages. Analyses of defensive secondary metabolites revealed age-specific variations under elevated CO2; 1- and 2-year-old A. contorta exhibited increased aristolochic acid concentrations in aboveground tissues while 10-year-old plants accumulated higher levels of magnocurarine and magnoflorine. These findings suggest a developmental shift in chemical defense, from early-stage investment in aristolochic acids to the use of alternative alkaloids in maturity. Increased concentrations of these metabolites under elevated CO2 may also reflect an adaptive response to herbivory pressure. These findings contribute to an adaptive framework for understanding how perennial species restructure growth and defense strategies across developmental stages in response to elevated CO2, with implications for predicting plant-herbivore interactions and ecosystem resilience under climate change.
Keywords: Aristolochic acid; C/N ratio; Climate change adaptation; Magnocurarine; Magnoflorine; Ontogeny; Plant defense.
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