The Study On Adaptation Of Droughty And Shade Stress Of Loropetalum Subcordatum

Loropetalum subcordatum was a rare and endangered species of Hamamelis. In order to explore its response mechanism of Photosynthetic Physiology from light and water, this study was to explore the difference of tetrathyrium subcordatum seedling growth and morphological, physiological and biochemical indexes as well as photosynthetic characteristics and chlorophyll fluorescence under different light conditions(L0-All lighting;L1-25% shading;L2-50% shading; L3-75% shading) by artificial shading. It was also experimented by drought and water control to explore the changes of physiological and biochemical indexes of the seedlings through different periods of drought treatment(CK?LD?MD?SD and FW) and different degree of water flooding(under normal water, half flooded and flooded).The main results are as follows:(1)Seedlings under the shade could significantly reduce seedling height, both stem and the average crown growth, a certain degree of shade could apparently increase the number of branches and it also had an impact on seedling survival rate, it was found 50%(L2) and 75%(L3) shading levels appeared a large number of plants died, the survival rates are only 66.67% and 40.00% at the terminal period; Seedlings under severe shading(L2 and L3) significantly reduced the seedling leaf area and petiole length and leaf number; Different light treatments had no significant effect on specific leaf weight, but the shade could markedly increased the root/shoot ratio and seedling biomass. It showed heavy shade(L2 and L3) root shoot ratio are 1.36 times and 2.23 times as that of shade(L0).(2)The study of Physiological Adaptability of shading showed that seedlings under shading conditions, superoxide dismutase(SOD) is low in light shade,while it was notably increased in excessive shaded environment; The soluble protein was prominently increased and sugar was reduced with the increasing degree of shading; With the shading stress, malondialdehyde(MDA) decreased significantly, whereas shade(L2 and L3) and light IV irradiation(L0) would dramatriaclly decreased the content of proline; long time of shading stress, the chlorophyll a,b and chlorophyll content were lessened gradually with the increasing shading intensity(L0), but a/b of chlorophyll was significantly higher comparatively.(3)As the light response curve showed, moderate shade could improve the photosynthetic rate of seedling leaf, the size of the Pn followed by L1>L0>L2>L3. tetrathyrium subcordatum saplings regularly adapted to the decrease of light intensity by reducing Pnmax?LSP? LCP and RD and elevating AQY light. While moderate shade treatment(L1) could increase the Pnmax and LCP, excessive shading would have the opposite effect,where the maximum pnmax in L1 processing group was 4.23 mol CO2·m-2·s-1, 30.96% higher compared with the control group L0.(4)The value of the initial fluorescence(F0) and the maximum fluorescence(Fm) and the maximum variable fluorescence(Fv) and PSII primary light energy conversion efficiency(Fv/Fm) could significantly increase in the short term under moderate shade, but it was declined with light stressing,compared with the control groups, and the maximum value appeared in L1 and L2. However, their values were both lower than in the early after 3 months shading treatment; With long time of comparatively heavy shade, chlorophyll fluorescence Y(II) and ETR were decreased, but NPQ values remained relatively stable as early,whereas the value increased firstly and then decreased with the increasing shading degree, where the severe(L1 and L2) shading levels were significantly reduced.(5) It could be concluded that through the study of continuous drought and rewatering test, the total activity of MDA of leaves and soluble sugar content continued increasing under drought stress, soluble protein value decreased firstly and then increased but were restored to normal levels after rewatering(FW).The activity of SOD tends to be reduced with the increase of drought stress and the activity of the redox ability in severe drought was lessened,and photosynthetic product output was also decreased.What's more,the permeability of MDA plasma membrane was increased but cell membrane was damaged and some indicators could be restored to baseline after rewatering; Drought stress also caused degressive tetrathyrium subcordatum chlorophyll a, chlorophyll b, chlorophyll content and the chlorophyll a/b value but their value could be recovered to the baseline after rewatering.(6) Water test results showed that values of tetrathyrium subcordatum SOD, MDA, proline and metabolites(soluble protein and soluble sugar) were slightly increased at the earlier flooding period.While in the flooding experiment, its value in the condition of semi submerged and completely submerged under test were dramaticlly lower than the initial value, and it was comparatively higher with half submerged treatment.Besides,the physiological indexes from semi submerged treatment were restored to baseline after rewatering, but the whole submerged tetrathyrium subcordatum SOD, soluble protein and proline could not be recovered; The varying patterns of chlorophyll a, chlorophyll b, total chlorophyll and chlorophyll a/b were similar, their value were increased slightly in the semi submerged and short-term flooding conditions,but in the long-term flooded environment.They declined significantly.Simultaneously,the related chlorophyll content could be restored to baseline, but they might fail to achieve that under long-term flooding.