Effects Of Waterlogging On The Growth And Physiological Characteristics Of Phoebe Zhennan S.Lee Saplings

Waterlogging disaster is a long-term water stagnation or suffer from groundwater immersion,the physical and chemical properties of soil deterioration,water,heat,gas and nutrient disorders,affecting plant growth and even endanger its survival.Waterlogging stress poses a serious threat to plant growth,distribution and population structure,as well as tree yield and product quality,which seriously affect agroforestry production.Due to climate change,rainfall in southern China is frequent,the frequency of flood disaster is increasing and the scope of harm is increasing year by year.At the same time in some low-lying areas and the valleys of in mountain areas the incorrect choice of afforestation aera,resulting in some young trees,middle age forest is often affected by waterlogging.Therefore,in-depth study of waterlogging stress has important scientific and practical significance.In this study,a field experiment was conducted to study the effects of waterlogging stress on the growth of 3-year-old saplings of Phoebe zhennan S.Lee from 2 provenances(Ya’an and Dujiangyan),analyzed the effects of waterlogging stress on root physiology,the responses of the photosynthetic Characteristics and growth dynamics of Phoebe zhennan Saplings to waterlogging stress.This study sttempted to reveal the correlation between each index and soil water content.The soil water content was treated as three levels which were 24%,27%and 31%of the soil volumetric water content,and took 24%as the control(CK)。The three levels were about 70%,80%,90%of the forest soil water holding capacity which were as a control,mild waterlogging and severe waterlogging,respectively.The results showed that:(1)The soil water content(SWC)in yang stand of the two provenances was not obvious,and the SWC under severe waterlogging stress was significantly higher than that of the control.And the monthly rainfall was positively correlated with the monthly SWC.(2)Before early July,the root activity of Zhennan saplings from 2 provenances under waterlogging was lower than the control,however,it is on the opposite during end of August;and the root activity of Zhennan saplings from Ya’an provenance was significantly higher than that of Dujiangyan provenance.In addition,root activity was positively correlated with SWC.The activity of superoxide dismutase(SOD)and the content of hydrogen peroxide(H2O2)which were from root of Zhennan saplings increased with the increasing degree of waterlogging,also,the content of superoxide anion O2-increased at the end of August with the increasing degree of waterlogging.Meanwhile,the H2O2 was positively correlated with the SWC.(3)The photosynthetic pigment content almost decreased with increasing degree of waterlogging stress except that of Ya’an provenance at the end of August.In addition,the chlorophyll a/b was significantly different from that of the control,and chlorophyll/carotenoid(Chi/Car)was decreased under the severe waterlogging stress.With increasing degree of waterlogging stress,the net photosynthetic rate(P,).stomatal conductance(Gs),transpiration rate(Tr)and intercellular CO2 concentration(Ci)decreased significantly,while the stomatal limitation value(Ls)increased obviously.It also showed that the photosynthesis of Ya’an provenance was stronger than provenance of Dujiangyan,With the increasing degree of waterlogging,CO2 compensation point(CCP)and light compensation point(LCP)showed an upward trend,while the maximum photosynthetic rate(Pn max)、CO2 saturation point(CSP).light saturation point(LSP)、RuBP carboxylation efficiency(CE)、photosynthetic respiration rate(Rp)and apparent quantum yield(AQY)showed a downward trend,and the Pn max under the severe waterlogging treatment was significantly different with the control.In addition,the photosynthetic physiological parameters were almost negatively correlated with SWC,Which indicated that the excessive SWC had a certain degree of inhibition on the photosynthetic physiology of Phoebe Zhennan.(.4)The growth(height,diameter and aboveground biomass)of Zhennan saplings from 2 provenances showed a decreased tendency with the increasing degree of waterlogging,which under the severe waterlogging treatment was significantly lower than that of the control.However,the net annual growth of ground diameter showed that:mild waterlogging treatment>control>severe waterlogging treatment.There was a significant positive correlation between SWC and the height,but SWC was negatively correlated with the diameter.In general,waterlogging stress inhibited the growth and physiology of Phoebe saplings to a certain extent.In summary,Zhennan saplings from Ya’an provenance not only have stronger photosynthetic capacity and ecological adaptability,but also have a higher stress tolerance,and the photosynthetic pigment content,Pn,gas exchange parameters and root activity decreased less than that of Dujiangyan provenance in the face of waterlogging stress.