The Physiological Response Of Hedysarum Mongolocum In Seeding Stage To Drought And Na Cl Stress

Hedysarum mongolocum is a sand shrub widely distributed in the northwest arid and semi-arid regions of China, very cold and drought resistant. Probing its physiological response to drought and salt stress and the mechanism is vital for its protection and utilization. This thesis use pot experimentexplored physiological effects of drought and salt stress on Hedysarum mongolocum, using 4 water stress treatments（i.e. 70%, 50%, 30% and 15% of relative water content）, 7 Na Cl stress treatments（i.e. 0, 5, 25, 50, 100, 200 and 300 mmol/L） and 4 osmotic potential（0, 0.25, 0.5 and 0.5 MPa） combine with low concentration Na Cl（0, 5, and 25 mmol/L）, the response of seedling photosynthesis characteristic, antioxidant properties, and osmotic regulation substances were investigated. The results showed as follows:1.The photosynthetic characteristics（except intercellular CO₂ concentration） in the MOD and SED treatments were significantly lower than CK, net photosynthetic rate and PS II potential activity in MID treatment increased 20.7% and 5.7% respectively. Antioxidant enzyme activity showed no significant difference between MID and CK treatments. The contents of proline, soluble sugar and K⁺ content in the leaves significantly increased with the increasing drought stress. Compared to CK, the contents of Na⁺ in leaves, roots and stems declined remarkably. These results suggest that Hedysarum mongolocum deal with drought stress by increasing SOD, CAT, POD activity and relative plasma permeability in leaves, improving contents of proline, soluble sugar, and selective absorption of K⁺.2.The Malondialdehyde content, relative plasma permeability, superoxide dismutase, catalase and peroxidase activity were significantly higher than CK when Na Cl concentration ≥100mmol/L. But 16.9% and 18.8% increase in plant height were observed under 5 and 25 mmol/LNa Cl treatment. No obvious difference was obtained in terms of proline, malondialdehyde content and relative plasma permeability under low Na Cl concentration（≤50mmol/L）. So low Na Cl concentration had no inhibiting effect and 5 to 25 mmol/L Na Cl could promote Hedysarum mongolocum seedling growth.3.The net photosynthetic rate, stomatal conductance, electron transport rate, chlorophyll content, PS II potential activity and PS II photochemical conversion efficiency decreased with the decreasing osmotic potential,（except intercellular CO₂ concentration increase）; While malondialdehyde content, relative plasma permeability, superoxide dismutase, catalase and peroxidase activity increased. The contents of proline, soluble sugar and K⁺ content in the leaves had significant increasing trends with the decrease of osmotic potential. Compared to CK, the contents of Na⁺ in leaves increased and then declined. All indicators of photosynthetic characteristics, antioxidant properties and osmotic showed that 25mmol/LNa Cl could improve Hedysarum mongolocum growth and its drought resistance.4.Under drought, salt and osmotic potential stress, Hedysarum mongolocum increased its antioxidant properties activity and relative plasma permeability in leaves, improved contents of proline, soluble sugar, and adjust K⁺ and Na⁺ ion homeostasis to reduce the stress and minimized the damage.