| To simulate water change in the water-level-fluctuating zone of the Three Gorges Reservoir Area (TGRA), six water treatment groups were applied in this research, including conventional water supply (C) as control, continuous half-submersion (HS), continuous full-submersion (FS), conventional water supply followed by light drought (CD), half-submersion followed by light drought (HSD) and full-submersion followed by light drought (FSD), the whole treatment includes 3 stages, maintains 166 days. This study sought to examine soil pH value, contents of organic matter (OM), total nitrogen (TN), total phosphorus (TP), total potassium (TK), alkali hydrolysable nitrogen (AN), available phosphorus (AP) and available potassium (AK), invertase activity, urease activity, phosphatase activity and hydrogen perxidase activity in M. glyptostroboides seedling soils under different water treatments.Results showed that, (1) in the condition of group C and HS, Metasequoia glyptostroboides saplings soils had very significant lower contents of nitrogen and TP compared with blank soils. AP content under H, nitrogen and TP contents in soils of group FS increased significantly after phase I. Compared with control (group C), flooding treatment increased the pH value and contents of OM, decreased AP content, while, the contents of TN, TP and AN increased 17.1%,16.9% and 34.2% in group H of M. glyptostroboides soils, respectively. Meanwhile, Compared with group C, soil invertase activity of group HS and FS decreased by 44.2% and 47.1%, urease activity fell 9.3% and 14.0%, and alkaline phosphatase activity fell 56.9% and 35.4% after short-term flooding (75d) respectively.(2) After the drought treatment of phase Ⅱ, prior flooding had detectable significant effect on subsequent sensitivity of pH value, contents of OM, AN and AP in M. glyptostroboides soils. Except for group C, the OM content in soils of all the Water treatment groups increased significantly in the soils planted M. glyptostroboides compared with blank group. At the same time, compared with group C, pH value increased by 2.6% and 3.8% in group HS and FS, however, the OM content was not significant difference in M. glyptostroboides soils. At the same time, after long-term flooding (145 d), compared with the control group, soil invertase activity of group FS was reduced by 26.3%, soil phosphatase activity of group HS, FS was reduced by 59.6% and 32.4%, urease activity increased 20% and 26.5%. By contrast, waterlogging did not make a significant impact on soil hydrogen perxidase activity. After drought treatment, compared with group CD, soil urease activity of group HD and FD decreased by 21.5% and 24.3%, while soil phosphatase activity was reduced by 62.5% and 44.6% respectively.(3) After water supply resumes normal of all of the treatments, the pH value of M. glyptostroboides soils in group HS and HSD decreased, while the OM content in soils of all the flooding treatment groups, the TN and TP content in soils of Group C, CD and CD increased significantly compared with the blank. The pH value and a number of other nutrient contents under flooding treatments recovered to the level of C group after recovery growth treatment. Meanwhile, all the chemical properties of HSD and FSD groups in M. glyptostroboides soils also recoverd to the level of group CD, and the activity of soil enzymes under different water treatment groups of M glyptostroboides seedings return to the level of control group except for hydrogen peroxide.(4) In addition, the correlation analysis of soil chemical properties in M. glyptostroboides saplings soils showed that the OM, TP, TN and the AN content had very significant positive correlation respectively. On the other hand, pH value displayed a highly negative relationship with the content of OM, TN, TP and TN. In addition, the correlation analysis of soil enzyme activities showed that except urease activity was positively related with the activity of alkaline phosphatase, there was no positive relationship among other enzyme activities in M. glyptostroboides saplings soils.Then, the chemical properties of soils in the in the water-level-fluctuating zone of the Three Gorges Reservoir Area under M. glyptostroboides saplings during a flooded cycle was studied. We planted the same M. glyptostroboides saplings on three elevation lines on September 15,2013, each line altitude fixed 6 strains of Metasequoia glyptostroboides saplings, a total of 18 strains. The soil samples were collected on June 7,2014 after a water level fluctuation cycle. Results of soil properties showed that:(1) pH value were significantly higher in the low (L) and middle (M) altitude elevation than that of high altitude (H) 3.14% and 2.91% respectively, while not significant difference was found among the three altitudes of the soil OM content.(2) TP content in soils of M. glyptostroboides saplings planted on M altitude were 1.02 times and 56.92% higher than L and M respectively, meanwhile, AK content was the highest on the M line among three elevation lines, increased 63.60% and 18.30% than L and respectively.(3) Hydrogen perxidase activity of the M. glyptostroboides saplings soils on altitude H and M increased 1.43 times and 1.01 times than L, invertase activity of H was 59.32% higher than M. At the same time, soil urease activity of H increased 2.12 and 1.02 times than L and M. In addition, soil alkaline phosphatase activity of M was significantly higher than L and H elevation lines.(4) The correlation analysis of soil properties in M. glyptostroboides saplings soils showed that there existed significantly or extremely significantly positive correlations between the the content of TN, AN and alkaline phosphatase activity, TP content were significantly or extremely significantly positive with invertase and hydrogen perxidase activities. There were significant relationships among soil enzyme activities, the hydrogen perxidase activity and was significantly positively related to invertase activity, and very significant positive correlated to alkaline phosphatase activity.The survival rate of M. glyptostroboides seedings was 100% throughout the whole phase of the simulating test, it can be one of the suitable tree species adapt to the water-level-fluctuating zone of the TGRA, while irrigation shoud be taked measures regularly during the dry periods. But the plants were all die after a flood period which pltanted on 165 m altitude line, which explains that Metasequoia glyptostroboides saplings were difficult to adapt to the complex environment of the water-level-fluctuating zone of the Three Gorges Reservoir Area for a long time. |
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