| A periodic water level gradient of hydro-fluctuation zone has been formed after the impoundment of the Three Gorges Reservoir (TGR). Due to the cyclical water level fluctuation all year round, the soils in this hydro-fluctuation zone annually experienced a series of gradient water change from drought to full flooding. Plants in theses areas are inundated when the TGR storing water in winter. In January, the water recession begins. However, when summer coming, the plants will confront mild drought when exposuring to high temperature in July. Thus, the plants in the hydro-fluctuation zone of TGR region are facing flooding to drought stress, which will then disrupt their circadian rhythm, and affect their growth and physiological process.In this research, four different water treatments simulating the soil water changes of hydro-fluctuation zone were applied to Distylium chinense, including control group CK (normally growing), continues root flooding group CF (flooding above5cm of soil surface), periodic flooding-drought group PF, and full flooding group TF (flooding above1.8m of plant top) at first. The growth, photosythesis and physiology mechanisms of D. chinense under different soil water contents were studied. Furthermore, to explore the adaptive mechanisms of D. chinense under flooding-drought stress, and to find compatible revegetation systerm for the revegetation of the hydro-fluctuation zone of TGR region, two vegetation configuration modes and three different water treatments were conducted. The modes were D. chinense+Cynodon dactylon (ZG) and D. chinense+Hemarthria sibirica (ZN), and the three different water treatments included control (CK), flooding above5cm of soil surface (T1) and full flooding (T2). In the study, the two modes were compared with other two normal modes, which were Salix variegata+Cynodon dactylon (QG) and Salix variegata+Hemarthria sibirica (QN). In the same time, the growth and physiology mechanisms of different plants in the four vegetation configuration modes under different soil water contents were also studied. The main results are as follows:1) The effect of water stress on growth and morphology of D. chinenseIn continues root flooding and periodic flooding-drought condition, D. chinense formed lenticel to get more oxygen, and resist hypoxia. Under continues root flooding and full flooding, the root of D. chinense turned brownish yellow to black, and gradually withered and decayed, while the leaf color of D. chinense under water stress was deep first, and then turned to shallow, compared to less affected color in the periodic flooding-drought group (PF). On the other side, the plant height, ground diameter (except for CF) and biomass of D. chinense under continues root flooding (CF), periodic flooding-drought (PF) and full flooding conditions (TF) were significantly lower than control (CK). With the extention of treatment time, the plant height, ground diameter (except for TF) and biomass of D. chinense under water stress gradually increased, so as the lenticel number in CF. The results showed that D. chinense is adapted to continues root flooding and periodic flooding-drought.2) The effect of water stress on physiological characteristic of D. chinenseWater stress significantly affected the chlorophyll content of D. chinense. The total chlorophyll content, chlorophyll a/chlorophyll b ratio and chlorophyll/carotenoids ratio of D. chinense in CF and TF were significantly lower than control, and reduced with the treatment time. However, the total chlorophyll content, carotenoid content and chlorophyll a/chlorophyll b ratio of D. chinense in PF had no significant difference to the control group.Different water treatments significantly influenced the net photosynthetic rate, stomatal conductance, intercellular CO2concentration and water use efficiency of D. chinense. Intercellular CO2concentration in CF, PF and TF was significantly higher than that in the control group respectively,while the plant’s net photosynthetic rates in CF, PF and TF were significantly lower when compared to CK. The net photosynthetic rate of D. chinense under water stresses decreased at the beginning of the experiment, and then gradually stabilized. The stomatal conductance of plant’s leaves in CF and PF decreased first, and there was a stable trend later as well, however, that in TF group was significantly higher than the control group throughout the experiment. The intercellular CO2concentration of D. chinense in CF and TF increased with the treatment time extended, with the comparison to increasing first, and then decreased in TF. Moreover, the water use efficiency of D. chinense in CF and TF decreased with the treatment time extention while it was increased in PF.Under continues root flooding and full flooding conditions, the root vigor of D. chinense decreased throughout the experiment, while there was no significant change in periodic flooding-drought group. The SOD (superoxide dismutase), POD (peroxidase), CAT (catalase), APX (ascorbate peroxidase) activity of D. chinense in CF, PF and TF increased with the increase of water stress. Indicating positive response of D. chinenseto the water stresses. With the treatment time extended, the protective enzyme activities decreased, but those in PF were higher than CF and TF respectively. Further more, the content of H2O2(hydrogenperoxide), O2·-(superoxide anion), MDA (malondialdehyde), free proline and soluble sugar of D. chinense under different water treatments was significantly increased, while the soluble protein content decreased significantly.3) The effect of water stress on the growth and physiological characteristic of D. chinense under different vegetation configuration modes and the comparation with other two modesVegetation configuration mode and water treatment significantly affected the root, stem, leaf and total biomass of the four plants (D. chinense, S. variegate, C. dactylon. H. sibirica), while there were no significant effects on the plant height and ground diameter. Different configuration modes did not significantly affect the protective enzyme activities, MDA, and osmotic adjustment substances contents of the four plant species, while water treatments significantly affected them. The plant’s protective enzyme activities, MDA, and osmotic adjustment substances contents in the experiment were changed, but different plants response to water stress differently. S. variegate growth slowly in QG and QN, indicating that C. dactylon and H. sibirica could negatively affect the growth of S. variegate. The biomass of C. dactylon siginificantly decreased in ZG, indicating that D. chinense affect the growth of C. dactylon. However, in the ZN mode, both of the two plants grew well and rapidly covered the ground. Moreover, the root system of D. chinense and H. sibirica were well developed, and could immobilize the soil well. Therefore, ZN mode surpasses other three modes. |
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