High-light and nutrient interactions drive carbohydrate and proton pump dynamics in Agastache rugosa (Fisch. &...

Agastache rugosa, a perennial herb native to temperate and subtropical regions, shows remarkable adaptive strategies when exposed to varying light and nutrient conditions in tropical environments. Our study reveals new insights into the crosstalk mechanisms involving carbohydrate homeostasis, biomass allocation, and nutrient acquisition in A. rugosa under different environmental conditions. Treatments were two light levels; HL (high-light, 0% shade) and LL (low-light, 50% shade), and four nutrient rates; NPK1 (40 mg kg^-1), NPK2 (80 mg kg^-1), NPK3 (120 mg kg^-1) and NPK4 (160 mg kg^-1). High-light coupled with increasing nutrient levels (HL-NPK3 and HL-NPK4) promoted biomass production via increased carbon assimilation, associated with higher soluble sugar levels and higher phosphorus and potassium uptake mediated by the upregulation of plasma membrane H⁺-ATPase. Maximum carbohydrate accumulation occurred at high-light and the lowest nutrient levels (HL-NPK1), coinciding with increased nitrogen uptake and the drastically high leaf nitrogen concentration. This response was preceded by the upregulation of acid phosphatase and sucrose phosphate synthase, suggesting a compensatory mechanism to maintain nutrient and carbohydrate reserves for critical metabolic processes. Starch increase was more apparent under low-light and higher nutrient levels (LL-NPK3 and LL-NPK4), relative to invertase downregulation, indicating a shift towards carbohydrate storage rather than utilization. These findings underscore the complex interplay between sugar signaling, nutrient sensing, enzymatic actions, and proton pump activity in modulating plant adaptation to varying environmental conditions. This study also highlights the importance of understanding how non-model medicinal species like A. rugosa reprogram their metabolism and resource allocation in response to environmental changes.