Response Of Mulberry And Water Birch Growth And Photosynthesis To Flooding Under Three Soil Types

Vegetation restoration and reconstruction have been paid more and more attention because of its low cost,sustainable and ecological environment.It is one of the effective ways to manage the ecological environment of the water-level belt in the Three Gorges reservoir area.Therefore,it is possible to adapt to the long-term water Flooding plants and clarifying their flooding mechanism is essential.In this article,two kinds of soil types of mulberry trees(Morus alba L.)and introduction of water birch(Betula nigra)in the 2-year-old reservoir area were used to study the water level of the Three Gorges reservoir area and the main soil types of purple soil,paddy soil and lime soil,the conventional water supply group(C)and semi-flooded group(F)were used to study the growth characteristics,photosynthetic physiology and soil nutrient contents of mulberry and birch in autumn and winter.And to provide a theoretical basis for the restoration and reconstruction of vegetation in the water-level-fluctuating zone of the Three Gorges Reservoir area.The main findings are as follows:(1)The purple soil in group C was weakly acidic,paddy soil and lime soil were alkaline.And soil nutrient content was also different,the specific performance of purple soil was higher than paddy soil,and paddy soil was higher than lime soil.Compared with group C,the pH value of F group was increased,and the pH value of paddy soil and lime soil decreased,finally,all of the pH value was neutral(pH=7).Soil organic matter,available N,available P and total N of 3 kind of soil were increased,while the soil available K content was opposite to that of the soil,and the change of soil P was not significant influences.There was no significant difference in the nutrient content of purple soil cultivated with mulberry and birch in group C.The change of soil nutrient content in paddy soil and lime soil was also the same,and there was no significant difference in the effect of mulberry and birch increasing soil fertility.The change of soil nutrient content in F group was the same as that of group C,which indicated that there was no significant difference in soil fertility between mulberry and birch under water-logging stress.(2)Under the natural conditions,the growth indexes of mulberry biomass,root growth,root vigor and root-shoot ratio of the three soils were higher than those of water birch,and the mulberry and birch in the purple soil were the best.Soils were the worst,indicating that mulberry roots were more developed than birch,and biomass accumulation was significantly affected by soil fertility.The biomass of mulberry and birch in the three soils was significantly inhibited under water-logging stress.Compared with the control,the root dry weight of mulberry and water birch were 34.09% and 29.01%,respectively,and the dry matter accumulation The average decline was 13.36%,11.49%,the total biomass decline were22.69%,17.53%.At the same time,the root-shoot ratio of the two tree species decreased significantly,indicating that the effect of flooding stress on the growth of mulberry and water birch was more serious than that of the shoots.In particular,under the flooding stress,Root length,total surface area and root volume were decreased in different degrees,and the root vigor was also decreased.On the contrary,the average diameter of mulberry and birch increased.After 90 days of flooding,the number of adventitious roots of mulberry and birch in the three soils was generated,and the survival rates of the two tree species on purple soil and paddy soil were 100%.The survival rates on the lime soil were 85%,80%,indicating that the adaptation mechanism of mulberry and birch to flooding is a mechanism of oxygen barrier resistance,and has strong ability of flooding for long flooding.(3)The photosynthesis of mulberry and birch in three soils was significantly inhibited under flooding stress.The net photosynthetic rate of mulberry decreased to59.87~79.83% of the control group,and the net photosynthetic rate of water birch decreased to 67.24~69.98% of the control group.The stomatal conductance,intercellular CO2 concentration and transpiration rate of the two tree species decreased in different degrees compared with the control group,but the stomatal limitation value was higher than that of the control group,which indicated that the decrease of the net photosynthetic rate of mulberry and birch was mainly due to the stomata Restrictions are caused.At the same time,the contents of chlorophyll a and chlorophyll b in the two tree species decreased significantly,but the ratio of chlorophyll a/b was higher than that of the control group,which was closer to 3:1.After the flooding,the Fv/Fm of the mulberry and birch in the F group of the three soils decreased to a certain extent compared with the control,but remained at a high level.The trend of qP,ETR and ?PSII was similar to that of Fv/Fm the same,showing a downward trend,and its qN showed an upward trend.In addition,Mulberry and water birch have stronger tolerance to water flooding in winter and autumn,and its adaptation mechanism to water flooding is a combination mechanism of oxygen resistance and oxygen resistance,and is affected greatly by soilfertility.