Comparative Evaluation Of Adaptability Of Four Woody Plants Against Winter Flooding And Summer Drought

The Three Gorges Project has made outstanding contributions in the fields of power generation,flood control and river transportation,but also caused series of ecological problems such as water loss and soil erosion.Vegetation restoration is a key solution to the ecological problems,while the key point is to select suitable tree species.This paper takes Taxodium ‘Zhongshansha',Metasequoia glyptostroboides,Salix variegata,mulberry as research materials,and has conducted a series of pot experiments by simulating the environmental characteristics of the Three Gorges Reservoir Area(TGRA)and studied the morphology,physiological and biochemical reactions of the four plants against the flooding stress,drought stress and “flooding-drought” stress and their correlations.The comparison of the tolerance of the 4 plants against the 3 kinds of stress was also studied.Field investigation found that Taxodium ‘Zhongshansha' is an excellent vegetation restoration plant,which can survive in the area 168-175 meters above sea level in the TGRA,so Taxodium ‘Zhongshansha'has high scientific and practical value.This paper is divided into two stages,water stress and drought stress,to study the ability of four kinds of plants to resist water flooding,drought and “flooding-drought” stress.The first stage of this graduation experiment set two experimental groups: Flooding group(FG)and control group(CK).FG was treated by 40-day's flooding treatment while the CK was under normal management.After flooding treatment,four kinds of plants had different morphological adaptations to increase the ability to resist flooding stress.Surface of the Taxodium ‘Zhongshansha'and Metasequoia glyptostroboides leaves formed gas film.Taxodium ‘Zhongshansha'formed adventitious roots.The SLW(Specific Leaf Weight)of the FG leaves of Taxodium ‘Zhongshansha'?Metasequoia glyptostroboides?Salix variegata decreased significantly compared with the CK's,and this change improved gas exchange ability.All the four plants took adaptive photosynthetic changes after flooding stress.The chlorophyll contents of the four plants of the FG were considerably separately lower than the CK's,indicating that flooding stress influenced the progress of chlorophyll degradation or synthesis.The value of chlorophyll a/b of FG of Taxodium ‘Zhongshansha',Metasequoia glyptostroboides and mulberry was separately lower than CK's,indicating that these three plants can maintain relatively high photosynthetic efficiency by decreasing the chlorophyll a/b values.MDA content of the 4 FG plants increased compared with the CK's,while the root activity decreased,indicating that four kinds of plants had suffered damage when treated by flooding stress.The SOD,POD,CAT and APX activity of FG's leaves were significantly higher than CK's,and this change was the positive response of the plants to inhibit the MDA accumulation rate,maintained a relative stand degree of the physiological and biochemical activity after flooding stress.The contents of proline,soluble sugar and soluble protein of the 4 FG's leaves increased compared to the CK's,helping plants to maintain high water absorption and retention ability after flooding stress,and maintain the normal nitrogen metabolism.Soluble sugar content of Salix variegata of the FG was lower than the CK's,and the soluble protein content of mulberry in the FG was lower than the CK's,while the reasons wait for further research.The second stage set 3 groups: CC group(Control followed by control),CD group(Control followed by drought)and FD group(Flooding followed by drought).After the winter dormancy flooding,four kinds of plants were treated by 20-day's drought stress beginning from July 5,2016.The chlorophyll content and root activity of the 4 CD groups were significantly lower than those of CC group,and the MDA content of the 4 CD groups were significantly separately higher than CC groups',indicating that the degradation or synthesis of the four plants after drought stress was blocked.The increased MDA had caused cell membrane damage and affected the root activity.Chlorophyll a/b values of the four CD groups were separately lower than those of the CC groups,which indicated that the chlorophyll a/b value could be adjusted to maintain the relative stand photosynthetic efficiency.Four kinds of antioxidant enzyme activities and the contents of the three kinds of osmotic adjustment substances of the plants in the 4 CD groups were higher than those of the CC groups.The results showed that four kinds of plants could adapt to drought stress by modifying the activity of antioxidant enzymes and the content of osmotic adjustment substances.Four kinds of plants can take physiological and biochemical response to drought stress,with a certain degree of drought tolerance.The chlorophyll content and chlorophyll a/b values of 4 FD groups were lower than those of CC groups.The antioxidant enzyme activity and osmotic adjustment substances in 4 FD groups were higher than those of CC groups.The results showed that four kinds of plants could adapt to flooding-drought stress by adjusting the activity of antioxidant enzymes and the content of osmotic adjustment substances.However,the different growth rate indicated that the four kinds of plants depended on different physiological and biochemical responses to enhance the ability to resist the floodingdrought stress.Under the flooding-drought stress,there was a significant positive correlation between MDA with SOD,POD and proline content in Taxodium ‘Zhongshansha',indicating that Taxodium ‘Zhongshansha' mainly depended on these three substances to inhibit the accumulation of MDA.The significant positive correlation between MDA with CAT and APX in Metasequoia glyptostroboides,and significant negative correlation between MDA with root activity,indicated the Metasequoia glyptostroboides mainly depended on increased CAT,APX content to inhibit the accumulation of MDA,and the increased MDA content of Metasequoia glyptostroboides affected its root activity.There was a significant positive correlation between the content of MDA with CAT,APX and soluble sugar,which indicated that Salix variegata mainly depended on the increased activity of CAT and APX and the content of soluble sugar to inhibit the accumulation of MDA;while MDA showed a significant negative correlation with the root activity in Salix variegata,showing that the increase of the MDA content influenced the root activity of Salix variegata.The significant positive correlation between the content of MDA with SOD and soluble protein in mulberry,indicated that the mulberry plants mainly depended on SOD and soluble protein to inhibit MDA accumulation rate.By using the membership function method found that the tolerance of the four kinds of plants against flooding stress ranked as follows: Salix variegata> Metasequoia glyptostroboides >Taxodium ‘Zhongshansha' >mulberry;the ability of tolerance against drought stress ranked as follows: Metasequoia glyptostroboides >mulberry Taxodium ‘Zhongshansha'> Salix variegata;the tolerance against “flooding-drought” stress ranked as follows: Salix variegata> Metasequoia glyptostroboides >Taxodium ‘Zhongshansha' >mulberry.In short,four kinds of plants are excellent ecological alternative restoration trees for the TGRA with outstanding ecological value and economic value,which can adjust the morphology,antioxidant enzyme system and osmotic adjustment system to adapt to flooding and drought stress.