Electrophysiological Insights into the Adaptability of Bletilla striata to Bicarbonate Stress in Karst Habitats

Bletilla striata, a perennial orchid of both medicinal and ecological value, exhibits remarkable adaptability to bicarbonate-rich karst environments. To elucidate its physiological and electrophysiological responses to bicarbonate stress, seedlings were cultivated for 45 days under NaHCO3 concentrations of 0, 5, 10, and 15 mM (n = 4), with the nutrient solution renewed daily. At 5 mM, biomass, chlorophyll content, electrophysiological traits, nutrient transport, metabolic indices, and conductance&ndash:resistance parameters did not differ significantly from controls, while intracellular water-use efficiency exhibited only a minor, non-significant increase&mdash:indicating stable physiological performance under low bicarbonate conditions. By contrast, higher concentrations (&ge:10 mM), particularly 15 mM, markedly reduced intracellular water-holding capacity (&minus:35.90%), nutrient translocation capacity (&minus:22.26%), and metabolic activity (&minus:50.00%), alongside electrophysiological signatures of diminished capacitance (&minus:48.69%) and elevated resistance (+147.61%), consistent with membrane injury and impaired ion transport. Although xylem pathways dominated HCO3&minus: transport, the phloem&mdash:despite greater sensitivity&mdash:showed an increased relative contribution under stress, supporting partial compensatory allocation. Metabolically, severe stress induced a shift toward a &ldquo:low-metabolism, high-efficiency&rdquo: strategy, prioritizing water conservation over carbon assimilation. Collectively, Bletilla striata adopts a dual strategy: maintaining functional stability (and modest enhancement) under environmentally relevant bicarbonate concentrations, while shifting to conservative resource-use under excessive stress. These adaptive mechanisms highlight B. striata&rsquo:s potential for ecological restoration and sustainable cultivation in bicarbonate-rich karst environments.