| Salinization has become one of global problems. Plants growing on saline soilwere severely inhibited by salinity, which is the main reason for restricting thedevelopment of agroculture and forestry. Biological techniques such as selectingsalt-tolernat germplasm resources are widely used to improve the ecologicalenvironment, avoid the waste of land resources of saline soils, which can also have acertain economic value.Elm tree (Ulmus pumila L.) is perennial woody plant, whose drought resistanceability is universally recognized, there have been reported that Elm tree can resist highsalinity. Understanding of physiological and ecological mechanisms under salt stress,are important for plant extension on the saline land. In this thesis, one-year-old elmseedlings in the Yellow River Delta region was used to study the growth andphotosynthesis characteristics under salinity Elm seedlings cultured in sand underdifferent NaCl concentration were used to measure the photosynthesis characteristicsand physiological parameters. Moreover, reasons for leaf abscission induced by highsalinity (300mmol·L-1NaCl) were investigated by analyzing ionic content,photosynthesis and endogenous hormones. The mian aims were to look insight intosalt resistant mechanism of elm tree.The main results are showed as follows:1. Elm is high salt resistant. The growth of elm seedlings under different NaClconcentrations (0,100,200,300mmol·L-1) was inhibited. Under100mmol·L-1NaClconcentration, the content of chlorophyll a，chlorophyll b and total chlorophyll of elmleaves were slightly lower than those of control, but with increase of NaClconcentration the above parameters declined. When NaCl concentration increased to200mmol·L-1, elm seedlings firstly showed dwarf, leaf colorosis and then turned to yellow and dry, fianlly leaves fall off, which indicated that elm seedlings can toleratehigh concentrations of salt stress.2. Elm seedlings under high NaCl concentration (300mmol·L-1), whose oldleaves are affected firstly, characterized by decline in leaf water content andphotosynthetic pigment and photosynthesis, by increase in membrane permeabilityand lipid peroxide levels, Na+and Cl-contents. Then leaves turned to yellow and dryand finally fall off. Salt injury symptoms of mature and young leaves occurred laterthan old leaves.3. Under300mmol·L-1NaCl concentration, Na+content in mature leaf wasalmost as2times as that in young leaves, Na+/K+ratio could achieve3times as muchas that in young leaves. Na+and Cl-preferred to accumulate in old leaves or matureleaves than expending leaves, which could reduce the salt damage to young leaves,being important for elm seedlings to survive and reproduce in high salinityenvironments. Under high salt stress, leaf abscission reduced the accumulation of saltin the plant body temporarily to avoid stress injuries.4. Under high salt stress, the old leaves became yellow and aging was associatedwith decrease of IAA/ABA ratio. After removal of salinity for a time, mew axillarybuds generated. In the treatment group of axillary buds, GA and IAA contentincreased by15.1%and28.5%respectively, However, ZR and ABA content was notchange significantly. Root cells were still alive, offer possibility to plant regenerationunder suitable conditions, which was necessary for plants to grow normally.5. Plant salt resistance includes salt escape and salt tolerance. The results of thiswork show that elm plants showed salt tolerance mainly through reducing growth andstomatal conductance to adapt to low salt concentration. While in high saltconcentration, elm showed salt escape mechanism mainly by falling off the old leavesto avoid salt injury. In particular, meristematic tissues such axillary bud, shoot tip androot tip remained active after the leaves fall off all, guaranteed for plants’ survivalafter salt stress removed or markedly reduced. |
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