The Effect Of Drought And Water-logging Stresses On Ecophysiology Of Cinnamomum Camphora Seedlings

Under global climate warming,drought and flooding are expected to increase in frequency and intensity in the future.Some studies found that drought and flooding had negative effects on trees.However,the effects of drought and water-logging stresses on eco-physiology of Cinnamomum camphora seedlings are not well understood.Moreover,the capacity of C.camphora after stress is less studied.In this thesis,one year old potted C.camphora seedlings were treated by drought and water-logging stresses and rewatered after drought stress.This thesis investigated the effects of drought and water-logging on carbon-water relations,nitrogen-phosphorus concentrations and biochemical traits,aiming to uncover the eco-physiological response strategies of C.camphora seedlings under drought and water-logging stresses.Results may help to provide theoretical basis for accuratly predicting and assessing the effect of changing rainfall patterns accompanied with climate change on trees.Futhermore,the tolerance of C.camphora to the two water stresses can be determined,thus providing theoretical reference for cultivatation,plantation and management of C.camphora and ecological restoration under climate change.The results show that:?1?the biomass of C.camphora was decreased by 42%and 26%under drought and water-logging stress,respectively.Drought stress enhanced the ratio of root to shoot?R/S?,but reduced the leaf mass fraction?LMF?.Water-logging stress reduced the ratio of root to shoot and the root mass fraction?RMF?,while it elevated the LMF.?2?Leaf water potential was reduced as drought progressed.However,leaf water potential was changed less under water-logging.Drought and water-logging stress reduced the photosynthesis at saturated light(A_sat),stomatal conductance?g_s?and transpiration rate?E?of seedlings.There is no significant difference between the effect of drought and water-logging stress on A_sat,g_s and E.There is a positive correlation between the A_sat,g_s and E with leaf water potential.Meanwhile,drought stress increased the instantaneous water use efficiency?WUE?and carbon isotope composition(?¹³C)of seedlings.Water-logging stress did not significantly affect the WUE and?¹³C.?3?Drought stress caused a significant reduction in total non-structural carbohydrate?NSC?and starch concentrations?ST?in roots and stems,while it did not have significant effects on total NSC and ST concentration in leaves.Water-logging stress reduced total NSC and ST in roots,but increased total NSC and ST concentration in stems and leaves.Drought and water-logging stresses did not have significant effect on soluble sugars?SS?.Drought stress increased the ratio of SS to total NSC in root,while water-logging stress increased the ratio of SS to total NSC in root.The effect of water-logging on stem and leaf NSC allocation was opposite to that of roots.?4?Drought and water-logging stress did not have significant effects on nitrogen and phosphorus concentrations in leaves.?5?Drought stress caused an increase in the concentrations of proline?Pro?and abscisic acid?ABA?in the leaves.?6?When rewatering under two drought stress conditions(i.e.g_s close to 0 and?_x close to?₅₀),leaf water potential were recovered to well watered status after one-day rewatering,but A_sat,g_s and E of the leaves were recovered much slower than leaf water potential.Besides,the time for g_s to return to one third of the control value was different for both drought conditions?the latter was1 day later than the former?.?7?After 1 day of rehydration from?_x close to?₅₀ stress,the leaf proline concentration decreased to the control level.After 1 day of rehydration from g_s close to 0 stress,the ABA concentration of the leaves dropped to control level.But after 1 day of rehydration from?₅₀ stress,leaf ABA concentration was siginificantly higher than control treatment.This thesis has shown that drought stress not only reduced the biomass,leaf water potential,A_sat,g_s,E,roots and stems total NSC and ST concentrations,but also increased the WUE,?¹³C,leaves Pro and ABA concentration.Water-logging stress reduced the biomass,A_sat,g_s,E,roots total NSC and ST concentrations,increased the total NSC and ST concentration in stems and leaves,while did not significantly affect the WUE,?¹³C,leaves Pro and ABA concentration.The rate of restoration in A_sat,g_s,E of C.camphora from drought stress was dependent on the intensity of drought.