| China was one of the most severely affected countries suffering from desertification. Haloxylon ammodendron (C. A. Mey.) Bunge (Chenopodiaceae) was an xerophytic desert shrub. As dominate desert plant, H. ammodendron played an important role in the maintenance of the structure and function of the whole ecosystem. During the last five decades, overall land reclamation and cultivation, over-grazing and over-cutting and digging had resulted in the destruction of H. ammodendron vegetation and development of mobile sand dunes. At the same time the development of artificial regeneration of H. ammodendron plantation was very slowing. Desert ecosystems have a especially characteristic of drought and high temperature. In this study we found that extreme high land surface temperature of desert often resulted in severe stress for little H. ammodendron seedling, some should be slowing down growth, the other should die. First, we studied the method of cultivating container H. ammodendron seedling in the greenhouse in order to obtain experiment materials, and then invented a device assembled with electrical heat band and control temperature apparatus to simulate the land surface temperature of desert which can stressed H. ammodendron seedling. We compared the different changes of morphology and physiology when H. ammodendron seedlings were stressed by drought, high temperature, high land surface temperature, strong light in the greenhous. The basic traits of H.ammodendron seedlings which were stressed by LSF in the desert were felt out. In order to settle the difficult problem of low survival probability of seedlings in the artificial regeneration of H. ammodendron plantations, we invented two simple protective devices, such a tube device and adumbral net cover, to protect direct seedling and replant seedling of H. ammodendron from resisting high land surface temperature stress, in which the survival probability of H. ammodendron seedling could been improved. We also studied the phenomenon of reproductive dormancy after flower of H. ammodendron and testified that this phenomenon was connected with the change of photoperiod. The contents as follows:1. This paper discussed the culture method of direct and replant container-seedlings of H. ammodendron, which included the preparation of medium, seedling separation, water temperature control in the greenhouse, control of pest and diseases. The results of experiment showed that this method have characteristics with rapid growth of seedings, area saving, feasible and simple for worker, mass production. This method breaks through the seasonal limiting and can supply seedling in advance for 2-3 months. All this provide convenience for development, research, and utilization of plant resources of H. ammodendron.2. There was a invention about a device which can simulate the land surface temperature of desert to stress desert plant. This device composed with electrical heat band, temperature controller, AC contactor, thermocouple. The results of experiment show that this device can normal work when length of electrical heat band< 25 m; and the temperature of each stress point have homogeneity, stability, and high precision.3. Using a device that were assembled with electrical heat band and control temperature apparatus to simulate the land surface temperature(LSF) of desert which can reach 60-70 ℃, we observed H. ammodendron seedlings were damaged dy LST stress with their assimilative branches slow growing, even ceasing growth, colour gradually turning from verdure into brilliant yellow,a few even dry up and fall off; at the same time the contents of soluble sugar, MDA, proline increased, activity of POD increased, activity of SOD decreased. The threshold value of H. ammodendron responded to LSF stress was 55℃. The damage responses could been passed from bottom to top and had the characteristic of gradual change, hysteresis. It was showed that temperature of the desert from the land surface to the -2cm layer often exceed 55℃ when we observed in the field.The response of the little seedlings and young trees were quick and apparent for LSF stress, however the grow-up trees were slow and inconspicuous. Water stress and LST stress together caused H. ammodendron seedlings to represent slow growing or ceasing growth in the summer.4. In the desert using simple device, such as tube device and adumbral net cover, to protect H. ammodendron seedlings in order to avoid water dissipation, reduce LST, prevent sand blown by wind, we wanted to improve the survival probability of direct seedling and replant seedling of H. ammodendron under the condition of no irrigation. The results showed that tube device had a significant protective function for direct seedling and replant seedling of H. ammodendron, thus caused the survival probability of direct seedling of H. ammodendron to reach about 33% which exceed the former method and approximately increase 60% under the condition of no irrigation; caused the survival probability of replant seedling of H. ammodendron to reach about 77% which exceed the former method and approximately increase 30% under the condition of no irrigation. Adumbral net cover had a good protective function for replant seedling of H. ammodendron, but had no protective function for direct seedling. H. ammodendron seedling maintained high survival probability, first depending on the protective device which can avoid water diaaipation and reduce LST, growing all right befter the middle of July, and then came into "summer dormence" after the first of August during the drought.5. Reproductive apparatus of H. ammodendron had evolved a particular procreative phenomenon such as flower in the springtime, reproductive dormancy after flower in the summer, rapid embryo development and fruit maturity in the autumn. We planted a number of container seedling of H. ammodendron, and select ecology factors (water, temperature, photoperiod) to do single factor test for finding pivotal ecology factor which might result in reproductive dormancy after flower(RDF); At the same time we observed H. ammodendron in the field in order to understand the reproductive characteristic. The results showed that the photoperiod is the pivotal ecology factor which can induce H. ammodendron to represent RDF when photoperiod became short in the autumn; Threshold value that H. ammodendron can sense the change of photoperiod and represent RDF was about 13h; For the development of fruit and seed, RDF of H. ammodendron is not essential process.H. ammodendron often be stressed by drought, high temperature, sand blown by wind and salt in desert ecosystems, but people usually ignore the land surface temperature stress which can damage H. ammodendron, especially its little seedlings. In this paper we showed that land surface temperature was not only an important factor of stress, but also resulted in a series of physiological reaction of vegetation when its was stressed, even could impacted the geographical distribution of desert vegetations. It was an important breakthrough of plant adversity physiology. Furthermore, the method of using simple device to protect H. ammodendron seedlings in order to reduce land surface temperature was the new advancement in the artificial regeneration of H. ammodendron plantations. |
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