| Joshua tree (Yucca brevifolia) as typical tree species in the western desert of America, it has developed root system and hold sand, for the evergreen tree species. Introduced into China in2009, it aims to accelerat the construction of desert area of vegetation and improv the ecological environment. Six biological agents, water retaining agent(T Ⅰ), ABT3(T Ⅱ), CCC (T Ⅲ), PP333(T Ⅳ),ABA(T Ⅴ) and SA(T Ⅵ),were applied to2-year-old desert plant Yucca brevifolia seedlings to study the effect and function of these biological agents on photosynthetic diurnal variation,survival rate, growth, physiological and biochemical indexes of it, and a comprehensive evaluation on their impact efficiency was drawn out, then get a suitable seedling biological agent for Joshua tree. The results were as followings:1. Water retention agent, ABT3and PP333processing of Joshua tree were significantly improved the photosynthetic rate of all day, the peak of Pn occurred at15:00, The peak of PP333is the highest reached19.57μmol·mol·s-1, is1.19times of that of CCC. And judging from the photosynthetic capacity of all day of Joshua tree of CCC, ABA and SA treatment is still lower than CK, experiments illustrated that the three types of processing is not able to improve the Joshua tree photosynthetic capacity.2. Water retaining agent ABT3significantly improve the survival and preservation rate of Joshua Tree, and mainly through chlorophyll increased, thus raising the net photosynthetic rate of Joshua tree seedlings, regulating plant photosynthesis; And through the change of osmotic regulation substances content regulation of plant osmotic potential, maintain moisture in plants; POD and CAT have respectively increase116.50%and165.76%on water retaining agent,; Compared with CK, maintained the balance of active oxygen in the body, increased resilience to stress; Water retaining agent and ABT3are the plant for the fine biological agents, can be used for large-scale in afforestation in the future.3. CCC and PP333made the survival and preservation rate of Joshua tree to be significantly reduced, the reason of CCC treat mainly was the lowest of water use efficiency, membrane lipid peroxidation, MDA accumulation is overmuch, cause plant leaf water-holding capacity is restrained, balance cell had damage, it is not conducive to plant grow in the desert environment and survival, the survival rate and preserving rate of decreased about15%; The reason of PP333treat probably due to concentration.4. The survival and preservation rates of Joshua tree applicated ABA and SA have increased slightly, and significantly increased the POD and CAT enzyme activity; CAT enzyme activity of Joshua tree applicated SA increased by214.24%than CK, and through the accumulation of soluble sugar, adjust the drought resistance of Joshua tree seedlings, makes the plant to better adapt to drought stress.5. Through principal component analysis, D-value was in the sequence of T Ⅰ> T Ⅳ> T Ⅱ> T Ⅴ>CK> T Ⅲ> T Ⅵ.It revealed that water retaining agent was the best biological agent,next to it was PP333,then ABT3was the third. Water retaining agent, ABT3and the suitable concentration of PP333can be used in large-scale afforestation as changes of afforestation measures to enhance the survival rate of plants, Joshua Tree seedlings to better adapt to the environment of the arid region, enhance the resistance of plants to achieve the maximum benefits of forestation.6. Studies show that the influence of the concentration of PP333to three kinds of antioxidant enzyme activity have different concentrations, the influence of the low concentration of PP333, SOD enzyme and POD enzyme activity are improved, in high concentrations it has certain inhibitory effect on enzyme activity, CAT enzyme activity change complex under different concentrations, but were higher than CK. The most suitable Joshua tree seedlings concentration should be chosen in the changes of100mg-L-1～150mg-L-1, low concentration can induce the activity of antioxidant enzymes improve better, thereby eliminating active oxygen damage to the plant, enabling them to better adapt to water stress. |
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