Rosli, K. A.; Misran, A.; Yazan, L. S.; Megat Wahab, P. E.

We investigated the physiological plasticity of Agastache rugosa (Fisch. & C.A.Mey.) Kuntze, in response to different light and nutrient levels, demonstrating complex adaptive strategies. Through comprehensive analysis of leaf traits, photosynthetic parameters, and resource use efficiencies, we uncovered unexpected patterns in Rubisco dynamics and nutrient utilization, particularly in low-light conditions. A. rugosa exhibited subtle thermal regulation, maintaining relatively stable leaf temperatures across treatments through coordinated adjustments in morphology and gas exchange. Multivariate analyses showed distinct clustering of traits, underlining the integrated nature of plant responses to environmental heterogeneity. Leaf area increased under low-light conditions, while leaf mass area was higher in high-light environments, consistent with shade avoidance syndrome and leaf economics spectrum theory. Surprisingly, Rubisco concentration and use efficiency were generally increased under low light, suggesting a compensatory mechanism. Water use efficiency was higher in high-light conditions, but photosynthetic phosphorus and potassium use efficiencies displayed surprising increases under low light. The species exhibited tight coordination between CO2 supply and demand, as evidenced by strong correlations between net photosynthesis, stomatal conductance, and carboxylation efficiency. Our findings suggest that A. rugosa employs a suite of physiological and morphological adjustments to optimize resource acquisition and utilization that contribute to its ecological success.