Studies On Physiological Characteristics Effects Of Cunninghamia Lanceolata Seedlings Under High Temperature Stress

Cunninghamia lanceolata is one of the most important timber species in southern China,which has fast-growing and high-yield products,excellent material properties and high economic value.With the intensification of the greenhouse effect and global warming,the high temperature weather in China frequently occurring,the growth of Chinese fir seedlings is effected seriously,which in turn affects the planting and development of Chinese fir plantations.In order to study the effect of high temperature on the growth of Chinese fir,promote the growth and precise management of Chinese fir seedlings,and improve the economic benefits of seedling raising.The high-yield decorative materials of Chinese fir were studied for the first time.The temperature control box was used to simulate the high temperature environment in summer.The growth,physiological and biochemical characteristics and photosynthetic characteristics of Cunninghamia lanceolata seedlings under high temperature stress were studied in this paper,and the correlation among various indicators was analyzed to explore the response and adaptability of seedlings to high temperature stress.At the same time,a preliminary study on the mitigation measures for the high temperature inhibition growth of Cunninghamia lanceolata seedlings was researched.The preliminary conclusions were founded as follow:(1)Hight temperature and strong light had significant inhibition effect on Cunninghamia lanceolata seedlings.The photosynthesis physiological indexes of Cunninghamia lanceolata seedlings changed significantly with the increase of temperature.Among them,the Rd rate increases linearly with increasing temperature.The LCP rose with the increase of temperature and showed the law of exponential change.The Pmax rate showed a quadratic curve,reached a maximum at 25℃ and decrease rapidly after 35℃;The Tr increased with the increase of temperature,and increased rapidly when the temperature exceeded 35℃,showing an exponential curve as a whole.The temperature and light intensity had synergistic effects,namely under high temperature and strong light conditions,the transpiration rate of Cunninghamia lanceolata seedlings will increase.Under the same light conditions,the WUE of Cunninghamia lanceolata seedlings decreased with the increase of temperature.At the same temperature,WUE increased first and then decreased with the increase of light intensity,and WUE was higher when the light intensity was 1000～2500 μmol·m-2·s-1.By analyzing the photosynthetic physiological indexes with the variation of temperature and light intensity of Cunninghamia lanceolata seedlings,the results showed that the fittable temperature for its growth was below 35℃ in summer,the optimum temperature was 25℃ and the suitable light intensity was 500～2000μgmol·m-2·s-1;High temperature and strong light will cause its photosynthetic rate inhibition phenomenon,and the transpiration rate will increase rapidly,and the water use rate will decrease rapidly,which will affect the growth of seedlings.Therefore,taking reasonable seedling measures,such as shading,spraying,controlling the appropriate temperature and lighting intensity of the seedbed can promote the growth of seedlings.(2)Long-time high temperature stress can lead to injury and even death to the Cunninghamia lanceolata seedlings.Long-term sustained mild high temperature stress(38℃/30℃)treatment caused slight damage to the leaves of the plants.After 7 days,the leaf tips became yellow.Under severe stress(42℃/34℃),the degree of damage of the seedlings was obviously enhanced.On the 3rd day,the leaf tips appeared yellow.After 7 days,a large area of needles and yellowing appeared,and the whole plant was in a wilting state,and even in more serious cases to die.The results showed that with the increase of high temperature,the tolerance and energy-saving ability of seedlings of Cunninghamia lanceolata seedlings to high temperature decreased significantly.(3)Long-time high temperature stress can significantly affect the physiological characteristics of Cunninghamia lanceolata seedlings.Under long-term mild high temperature stress,Rd and Rmax did not change significantly,Tr increased,Chlorophyll a,b and total content decreased continuously,carotenoids increased with the prolongation of stress time.Under severe high temperature stress,Rd decreased,Pmax decreased,and Tr increased first and then decreased,chlorophyll a,chlorophyll b and total content decreased and carotenoids increased more obviously with the prolongation of stress time.Long-term high temperature stress also had significant effects on other physiological indexes of the seedlings.Among them,The relative conductivity was increasing continuously and had extremely significant positive correlated with the heat damage index.SOD activity firstly increased and then decreased,and it is especially evident under severe stress,while POD increased firstly and then decreased slightly,and finally showed a steady trend.Proline content showed a tendency to ascend,and the proline in mild stress was weaker than in severe stress.Continuous mild high temperature environment will cause the content of MDA and soluble protein in the leaves of Cunninghamia lanceolata seedlings to increase continuously,while the continuous high temperature environment will cause the MDA and soluble protein to increase first and then decrease.The soluble sugar was slightly raise,and the soluble sugar in severe stress was stronger than in mild stress.However,the root activity and soil pH of the seedlings had no significant effect with the severity of stress and stress time.(4)Under high temperature stress,spraying 100μmol·L-1 salicylic acid solution can effectively reduce the damage of high temperature on Cunninghamia lanceolata seedlings.