Study On The Hydraulic Characteristics And Mechanism Of Drought Defoliation Of Populus Tomentosa Based On Plant Segmentation Hypothesis

Populus tomentosa is a famous native tree species in China.It is mainly planted in north China and northwest China,where were severely impacted by seasonal drought?spring drought and summer drought?frequently.and occasional drought in some years.Therefore,water stress is one of the main problems affecting the stand growth of P.tomentosa plantation.It was observed that in the dry season,there may be a few or even all leaves in the poplar and the leaves could be expanded again after rehydration.or dead.In this study,P.‘Beilinxiongzhu 1'and P.‘Beilinxiongzhu 2'were as plant materials and the hydraulic and functional characteristics of stem,petiolar and leaf of two varieties were compared by measuring the PV curve,hydraulic conductance and leaf water potential,stomatal conductance and other methods.Based on the plant segmentation hypothesis,the causes of dry season defoliation of P.tomentosa were analyzed from the water relationship of plant organs between hydraulic segmentation and vulnerability segmentation.The main results are as follows:?1?Two species of embolism vulnerability curve?₅₀ are sort of leaf>stem>petioles,which conforms to the hypothesis of plant segmentation to a certain extent.The leaf is more fragile than the stem and can protect the stem from cavitation.?2?In drought-prone months,the predawn leaf water potential and the midday leaf water potential of P.‘Beilinxiongzhu 1'were more stable than that of P.‘Beilinxiongzhu 2',the stomatal conductance was not correlated with the predawn water potential,and the stomatal conductance was related to many environmental factors.?3?According to the perspective of the parameters of two clones drought resistance,turgor loss point osmotic potential(?_tlp),relative water content at turgor loss point osmotic potential(RWC_tlp)and water capacity(C_leaf)of P.‘Beilinxiongzhu 1'were higher than those of P.‘Beilinxiongzhu 2,indicating that the drought resistance of P.‘Beilinxiongzhu 2'was stronger than that of P.‘Beilinxiongzhu 1'.?4?Compared with the general values of trees,the ratio of specific leaf weight of P.‘Beilinxiongzhu 1'and P.‘Beilinxiongzhu 2'was lower,indicating shorter leaf life.Stem density in general,indicating that the anti-cavitation ability of stem is general.The data of hypothesis and vulnerability of P.tomentosa basically accord with the plant segmentation hypothesis,which indicates that it is possible to maintain the hydraulic structure and function of the stem through shedding leaves.It is revealed that the hydraulics reason that P.tomentosa can not only grow rapidly under the condition of sufficient water and fertilizer,but also survive through the deciduous leaves under the condition of occasional extreme drought.Of course,the regeneration of dry leaves may also involve special physiological and biochemical functions in their bodies,which need further study.