Responses Of Different Clones From Hybrid Tulip Tree To Drought Stress

The hybrid tulip tree (Liriodendron chinense×L. tulipifera) is a kind of tree whichis badly in need of cultivation for ornamental and industrial material in recent yearsin China.With the aim of laying a solid foundation for breeding drought- resistance hybridtulip tree and offering scientific basis for its promotion and application, tweleveclones of hybrid tulip tree were adopted to study on the change of appearance,physiological biochemistry characteristics which related with environment stress,the endogenous hormones as well as the photosynthesis characteristics under waterstress conditions. The main results were shown as follows:1. All clones were injured to various degrees under water stress conditions. Theleaves became yellow and the chlorophyll content reduced. The change was slowerin drought-resistance clones. According to the drought injury index, NE55, NE25,NE78and NE22 clones had resistance to water stress. However, NE38, NE23andNE04 clones were sensitive to water stress.2. During the process of the water stress, the research on leaves water contentof different clones indicated as follows: The FWC and RWC reduced obviously, theBWC rose on the contrary, BWC/FWC assumed the trend of escalation. Drought-resistance clones could maintain higher RWC and BWC adjustment ability, the RWDrose slower and changed smaller.3. During the process of the water stress, membrane penetrability and MDAcontent in leaves of all clones increased, the increase was less in drought-resistanceclones. The change of SOD and APX activities had differences in time and range;drought -resistance clones could keep high enzyme activities. At the same time, thesoluble protein content in leaves changed and free proline content rose, more freeproline were tested in drought -resistance clones.4. The changes of endogenous hormones under continuous water stressconditions indicated as follows: ABA accumulated in leaves of different clones anddrought -resistance clones rose slower; IAA content showed a decreased trend; thedecrease was higher in drought-resistance clones during the period of water stress;ZR content changed different respectively and reduced during the later period ofwater stress; JA content increased, drought-sensitive clones had to maintain higherJA content to resist water stress.5. During the process of the water stress, the stomatal conductance,transpiration rate and net photosynthetic rate of all clones decreased, but intercellular CO₂ concentration showed a trend of rise-fall. With the fluctuations ofstomatal limit, the main decreased reason on different clones' photosynthesis wasstomatal limitation during the earlier period, along with water stress degreeaggravating, non-stomatal limitation become the main reason. Drought-resistanceclones could maintain higher photosynthesis ability and WUE.6. The changes of chlorophyll fluorescence under water stress conditionsindicated as follows: Fv/Fm, yield and qP in leaves of all clones decreased, while Foand qN raised dramatically. Analysis indicated that photosystemâ…¡damaged, andprimary light energy conversion of PSâ…¡(Fv/Fm) dropped. Photosynthetic electrontransport, photosythetic primary reaction were inhibited. Heat disseminates whichpossess photoprotective effect increased. But each parameters varied differencebetween clones under water stress conditions. The change was slower indrought-resistance clones. This implied that there was a closed relationship betweenthe effects of water stress on chlorophyll fluorescence parameters of different clonesand its drought-resistance.7. Twenty-seven physiological and biochemical indexes which related withenvironment stress were treated by using principal component analysis andsubordinative function to make comprehensive evaluation to different clones, thesequence of resisting to water stress was ranked as follows:NE78＞NE22＞NE25＞NE52＞NE19＞NE55＞NE75＞NE28＞NE38＞NE04＞NE23＞NE06.