| The hydrology of Three Gorges Reservoir(TGR)area had formed a hydro-fluctuation zone with a vertical height difference of 30 meters.The original plants in the hydro-fluctuation zone died out because they could not tolerate high-intensity,long-term and winter submergence,which in turn caused a series of ecological and environmental problems in the TGR.In order to solve the ecological environment problem in the hydro-fluctuation zone of the TGR area,it is an effective method to select suitable vegetation for vegetation reconstruction.There was a clear need to study tolerance to submergence of suitable plants in the hydro-fluctuation zone and to understand their physiological and ecological adaptation mechanism in the actual habitat,which could provide a theoretical reference for the research on the tolerance mechanism of suitable plants,the reconstruction and management of vegetation in the hydro-fluctuation zone of the TGR.The study selected Taxodium ascendens and Salix matsudana which were planted in the from 165 m above sea level(a.s.l.)to 175 m a.s.l.in the vegetation reconstruction demonstration base of the TGR area in Zhong County,Chongqing in March 2016.The sampling trip was divided into three parts based on the depth and time of submergence,control-CK(175 m a.s.l.),moderate submergence-MS(170 m a.s.l.)and deep submergence-DS(165 m a.s.l.).The height and base diameter of two plant species were measured and the roots and shoots were collected in early period of de-submergence and end of recovery period.The non-structural carbohydrate content and metabolic enzyme activity in root and shoot was analyzed.The research results are as follows,1.Winter submergence had negative impacts on the growth of T.ascendens and S.matsudana,but the two species showed good growth adaptability,and the impact of deep submergence on the growth of S.matsudana was worthy of continuous attention.The results showed that the water-level changes of hydro-fluctuation in the TGR area had impacts on the growth of the T.ascendens and S.matsudana.(1)High-intensity and long-term winter submergence inhibited the plant height and base diameter of two woody species in different degrees,and the impacts on the S.matsudana were more significant.(2)With the increase of winter submergence,the root and shoot biomass of two woody species reduced significantly.(3)The plant height and biomass of T.ascendens increased significantly in the end of recovery period compared with the early period of de-submergence,and the base diameter increased to varying degrees.(4)The plant height,base diameter and biomass of S.matsudana in MS group and the plant height in DS group increased significantly in the end of recovery period compared with the early period of de-submergence.However,the base diameter and biomass in DS group increased nonsignificantly in the end period of the recovery.2.The winter submergence reduced the accumulation of non-structural carbohydrates in T.ascendens and S.matsudana,but the non-structural carbohydrate content increased to normal levels in end of recovery period.Water-level changes of the TGR had an impact on characteristics of non-structural carbohydrate(Soluble sugar,starch,sucrose and fructan)of the T.ascendens and S.matsudana.(1)Winter submergence significantly inhibited the starch content in roots and soluble sugar content in shoots of the submergence groups T.ascendens,but had no significant effect on the rest of non-structural carbohydrates.(2)Winter submergence inhibited the sucrose in the roots of the MS group and the fructan content in shoots of the DS group,but affected the rest of non-structural carbohydrate content nonsignificantly.(3)The winter submergence had no significant effect on the distribution of non-structural carbohydrate between root and shoot,the accumulation of non-structural carbohydrates in two suitable woody plants was inhibited by different degrees of winter submergence.(4)After the recovery of de-submergence period,the non-structural carbohydrate content reached or even exceeded the control level,which reflected that the two woody plants respond to the upcoming winter submergence by strengthening the reserves of non-structural carbohydrates,demonstrating a good adaptability to the water level changes in the hydro-flactuation zone of the TGR area.3.T.ascendens and S.matsudana reduced the sucrose and starch metabolism intensity during the submergence to adapt to the water level change in the water level of the Three Gorges ReservoirWater-level changes of the TGR area had an impact on characteristics of sucrose and starch metabolic enzyme activities of the T.ascendens and S.matsudana.(1)The effects of winter submergence on the sucrose and starch metabolic enzyme activities of the two woody plants were consistent.(2)After the winter submergence,the root metabolism of the two woody plants was more active than shoot.There was no significant difference in sucrose phosphate synthase activity between the submergence groups and the control group.The invertase,sucrose synthase and amylase activities in roots and shoots of the two woody plants in the submergence group were significantly lower than those in the CK.(3)In the end of recovery period,compared with shoots,the two woody plants were still more active in root metabolism.There was no significant difference in the metabolic intensity among three treatments in the two woody plants respectively,which indicated that T.ascendens and S.matsudana could actively adjust the intensity of metabolism to adapt water-level changes,reduce the metabolic intensity to survive the submergence,and reover metabolic intensity to the control level in end period of recovery.In summary,after planting of T.ascendens and S.matsudana in the hydro-fluctuation zone for nearly one and half year,the two woody plants had some adaptability to the hydrology of the water-level fluctuation zone.Submergence affected the metabolism of non-structural carbohydrate in two woody species,and its effects varied with non-structural carbohydrate types,metabolic enzyme types,and plant organs.Two woody plants spend a long period of high-intensity winter submergence by reducing their own metabolic intensity.In de-submergence period,T.ascendens and S.matsudana may balance the growth and storage of photosynthesis products,and make a carbohydrate reserve before the next submergence cycle to ensure the energy supply during the submergence and the exposure period.This study initially explained the reasons for the adaptation of T.ascendens and S.matsudana to the water-level changes in the TGR area from the perspective of non-structural carbohydrate consumption.T.ascendens and S.matsudana adopted a “Low Oxygen Quiescence Syndrome” strategy to reduce the metabolic intensity to survive submergence,and actively regenerate carbohydrates to restore growth in de-submergence period.However,the weakening adaptability of the DS group S.matsudana was worthy of our attention.It is recommended to strengthen the management of de-submergence period.Due to the repeated submergence of in the water-level fluctuation zone of the TGR area,it is necessary to carry out follow-up monitoring work on the T.ascendens and S.matsudana in the vegetation reconstruction base. |
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