Responses Of Carbon And Hydraulic Traits To Drought-Rewatering Of Liquidambar Formosana And Schima Superba Seedings

Global climate change has led to more frequently and intense droughts,which may have an adverse impact on tree growth and survival.The capacity for trees to resist drought and recover from drought is thus crucial for tree survival.However,it is still unclear how carbon and water relations of Liquidambar formosana and Schima superba?two tree species commonly used as pioneer species and soil and water conservation species?would respond to drought stress and rewatering after drought.,The differences in drought strategies between the two species still need further study.In this thesis,potted seedlings of L.formosana and S.superba were subjected to drought stress and rewatering after drought.Growth,hydraulic characteristics,gas exchange parameters,non-structural carbohydrate concentration were investigated during the experimental period.Results are shown as follows:?1?There are some differences in the hydraulic characteristics between L.formosana and S.superba seedlings.Compared with L.formosana seedlings,the?₅₀?the xylem water potential when the xylem hydraulic conductivity decreased by 50%?of S.superba seedlings was negative than L.formosana seedlings 68.18%.The C_leaf,g_min,C_branch of S superba seedlings were 54.76%,63.40%and 44.21%lower than those of L.formosana seedlings.The water loss resistance of S.superba seedlings is stronger than that of L.formosana seedlings.?2?Drought stress and rewatering had no significant effect on plant height,stem,root,stem,leaf biomass and allocation,total biomass and specific leaf area of L.formosana and S.superba seedlings.However,the root mass fraction of S.superba seedlings was9.53%³7.63%larger than that of L.formosana seedlings,and the specific leaf area was5.61%¹1.59%smaller than that of L.formosana seedlings.?3?Drought stress significantly reduced predawn water potential,midday water potential and xylem water potential of L.formosana and S.superba seedlings.After rehydration,the water potential of S.superba seedlings recovered to control values within0.5 days,while the midday water potential and xylem water potential of L.formosana seedlings were restored 6.5 days after rehydration.The leaf relative water content of S.superba seedlings decreased by 23.03%in drought process,and gradually recovered after rehydration.while the relative leaf water content of L.formosana seedlings did not change significantly during this process.The degree of stem xylem embolism of L.formosana and S.superba seedlings did not return to the level before the experiment until the end of the experiment?6.5 days after rehydration?.?4?Drought stress significantly reduced the gas exchange parameters?net photosynthetic rate,stomatal conductance and transpiration rate?of L.formosana and S.superba seedlings.On the 6th day of drought,there were almost no gas exchange parameters of L.formosana and S.superba seedlings.The gas exchange parameters of L.formosana seedlings were gradually recovered after rehydration and surpassed CK treatment,showing compensatory effects.Although the gas exchange parameters of S.superba seedlings were still 71.98%lower than that of the control at the end of the experiment?6.5 days after rehydration?.Drought stress significantly reduced the instantaneous water use efficiency of L.formosana seedlings,while the instantaneous water use efficiency of S.superba seedlings increased first and then decreased during the drought process.There was no significant change in water use efficiency of L.formosana and S.superba seedlings.during drought and rehydration.?7?Drought stress significantly increased the soluble sugar concentration of roots,stems and leaves of L.formosana seedlings and the soluble sugar concentration of roots of S.superba seedlings?37.09%⁸4.82%?.However,the starch concentration of roots,stems and leaves of L.formosana seedlings and the starch concentration of roots and leaves of S.superba seedlings were significantly lower during drought stress?15.30%³5.73%?.At the end of 6.5 days rehydration,the content of solubility sugar in roots and stems of L.formosana and S.superba seedlings was still 40.87%⁸2.99%higher than that of the control.The starch content in roots,stems and leaves of L.formosana seedlings and that in roots and leaves of S.superba seedlings were 10.69%⁶5.27%lower than that of the control.This study shows that the tolerance ability of S.superba seedlings to drought stress and the ability of xylem embolism repair after rewatering were stronger,which might be more advantageous in high-intensity continuous drought.And it may be more adaptable to seasonal periodic drought due to the rapid recovery of water carrying capacity of S.superba seedlings.However,the gas exchange parameters of L.formosana seedlings recovered quickly,and there was compensation effect after rehydration,which could make up for the loss caused by drought stress to a certain extent,and might be more adaptable to mild drought.The responses of L.formosana seedlings and S.superba seedlings to drought and rehydration were different,which indicated that they adopted different strategies to adapt to drought,the deciduous tree L.formosana survive drought by avoiding drought and the evergreen tree S.superba survive drought by resist drought.