Abstract: To understand whether exogenous calcium could alleviate damages in Polygonatum cyrtonema Hua caused by high temperature and strong light stresses, the effects of different Ca²⁺ concentrations on the photosynthesis and physiological indices of stressresistance of P. cyrtonema were assayed under high temperature and strong light environment. P. cyrtonema was cultivated in pots and irrigated with modified Hoagland’s solution with five Ca²⁺ concentrations (5, 10, 15, 20, 25 mmol·L^-1). Stress treatments were started by exposing plants to high temperature and strong light, with photosynthesis and physiological parameters being measured ten days later. The biomass of roots and stems and the contents of active compounds were measured after P. cyrtonema were tumbled. There were two controls, with plants being irrigated with Hoagland’s solution and cultivated at 25 ℃/shade, as well as under high temperature and strong light. The results showed that proper Ca²⁺ concentration alleviated damages of high temperature stress by enhancing the activities of SOD and CAT, inhibiting hydrogen peroxide (H₂O₂) and superoxide anion radical (O₂^-_·) accumulation, and reducing malonaldehyde content and relative conductance. Furthermore, the addition of Ca²⁺ increased chlorophyll contents, stomatal conductance, proline and soluble protein contents, maximal photochemical efficiency of photosystem II (F_v/F_m), effective quantum yield of photosystem II (Yield), relative electron transport rate (ETR) and photochemical quenching index (q_P) and decreased NPQ. The stressresistance of P. cyrtonema was declinedwith increasing Ca²⁺ concentration. In this study, Ca²⁺ concentration at 10 mmol·L^-1 alleviated stress damages in P. cyrtonema caused by high temperature and strong light and increased the yield and content of active compounds.

Key words: biological treatment, sulfonamides, antibiotic resistance genes, chemical treatment, disinfection, tetracyclines