Responses Of Water Transportation And Carbon Metabolism Characteristics In Haloxylon Ammodendron And Alhagi Sparsifolia To Drought Stress

Drought stress has always been the main factor affecting plant growth and death in arid and semi-arid areas.The response and adaptation of plants to drought stress has become one of the hotspots in plant physiology and ecology.Drought stress poses a serious threat to the homeostasis of plants.Because plants exchange with the atmosphere through photosynthesis,transpiration and other processes,and under drought stress,plants adapt to environmental changes by regulating stomata.This behavior makes plants face death from excessive carbohydrate consumption or hydraulic failure.Current studies have shown that plants reduce the effects of stomatal regulation on plants by changing the relationship between their traits and traits.Plant traits and their relationship can not only objectively describe the changes of plant internal physiological activities,but also clearly explain the internal and external changes of plants in the face of drought and the differences of drought response of different plants when the external environment changes.Haloxylon Ammodendron and Alhagi Sparsifolia is the dominant species of desert ecosystem,and it is drought resistant,saline alkali resistant and stress resistant plants.Both of them have the function of fixing sand dunes.Secondly,Haloxylon ammodendron and Alhagi Sparsifolia have higher ecological benefits and economic value.In this paper,Haloxylon ammodendron and Alhagi Sparsifolia in Ebinur Lake Nature Reserve were selected as the research objects.The morphological traits,hydraulic traits and carbon metabolism related traits(Photosynthetic parameters and Non structural carbon)of Haloxylon ammodendron and Alhagi Sparsifolia were measured outdoor on three drought gradients.Then,the differences between Haloxylon ammodendron and Alhagi Sparsifolia in response to drought were explored by using ANOVA,multiple comparison,principal component analysis and other methods.The results show that:(1)In the drought gradient,the tree height,canopy area and base diameter of Alhagi Sparsifolia didn't change significantly(P>0.05),but for Haloxylon ammodendron,only base diameter didn't change significantly with the increase of drought gradient(P>0.05);In leaf traits,with the increase of drought degree,the dry matter content of Alhagi Sparsifolia increased significantly(P<0.05),and other traits had no significant change.On the contrary,there was no significant change in leaf area(Haloxylon ammodendron leaves were replaced by assimilating branches)(P>0.05),but there were significant changes in other leaf traits(P<0.05).Specifically,specific leaf area decreased first and then increased(P<0.05),leaf diameter and dry matter content increased(P<0.05).The results of independent-samples T test and two-way ANOVA showed that both drought gradient and species could affect basic morphological and leaf traits.However,in the drought gradient,some morphological traits of Alhagi Sparsifolia and Haloxylon ammodendron showed convergence through environmental screening.(2)With the increase of drought degree,the leaf water potential and wood density of Alhagi Sparsifolia increased first and then decreased,but on the contrary,the branch water potential,leaf specific hydraulic conductance and Huber value decreased first and then increased,while the branch specific hydraulic conductance decreased continuously.The results of vulnerability curve showed that the anti embolism ability of Alhagi Sparsifolia in moderate drought sample plot was the strongest(P_50(moderate):-0.84 MPa<P_50(mild):-0.77 MPa<P_50(severe):-0.30 MPa).For Haloxylon ammodendron,with the increase of drought gradient,the leaf specific hydraulic conductance and branch leaf water potential decreased first and then increased,but the branch specific hydraulic conductance and Huber value increased first and then decreased,and the wood density increased continuously.The vulnerability curve showed that Haloxylon ammodendron had the strongest anti embolism ability in the mild drought plot(P_50(mild):-0.52 MPa<P_50(moderate):-0.42MPa<P_50(severe):-0.29 MPa).The results of independent-sample T test and two-way ANOVA showed that both drought gradient and species could affect hydraulic properties.However,in the drought gradient,some of the hydraulic properties of Alhagi Sparsifolia and Haloxylon ammodendron showed convergence.(3)With the increase of drought stress,net photosynthetic rate,stomatal conductance and transpiration rate decreased significantly(P<0.05),except for water use efficiency of Alhagi Sparsifolia and Haloxylon ammodendron(P>0.05).In terms of Non-structural carbohydrate,the contents of soluble sugar and total non-structural carbohydrate in Alhagi Sparsifolia and Haloxylon ammodendron increased gradually with the increase of drought stress(P<0.05);On the contrary,starch decreased gradually(P<0.05).The results of independent-sample T test and two-way ANOVA showed that net photosynthetic rate,stomatal conductance,transpiration rate and non-structural carbohydrate were affected by drought,and there were significant differences between Alhagi Sparsifolia and Haloxylon ammodendron.(4)Pearson correlation analysis showed that there were 28 pairs of traits significantly related to Alhagi Sparsifolia,which was much less than that of Haloxylon ammodendron(57 pairs),indicating that the regional range of correlation between traits of Haloxylon ammodendron was more extensive.The results of principal component analysis showed that the combination of Haloxylon ammodendron and Alhagi Sparsifolia was different in response to drought.Specifically,the 21 traits of Alhagi Sparsifolia could be divided into four categories,and the sum of variance was 79.13%.They mainly represent the material accumulation and transport group,morphological structure group,water transport dynamic group and leaf water transport group.The 21 traits of Haloxylon ammodendron can be divided into three categories,and the sum of variance explanation is 81.82%,which respectively represents the formation and material accumulation group,the branch and leaf water transport group,the morphological structure and the water transport group.The number of trait combinations of Haloxylon ammodendron is less than that of Alhagi Sparsifolia,and the combination mode of hydraulic traits,carbon metabolism traits and morphological traits is different from that of Alhagi Sparsifolia.This indicates that Haloxylon ammodendron and Alhagi Sparsifolia have different adaptive strategies of drought,and Alhagi Sparsifolia has more diversified strategies to cope with drought.The results showed that the morphological,hydraulic and carbon metabolism traits of Haloxylon ammodendron and Alhagi Sparsifolia changed with drought gradient;The response of traits of the two species to drought stress was significantly different,but in similar traits,environmental screening made their traits have convergence to a certain extent.Compared with Haloxylon ammodendron,the trait combination of Alhagi Sparsifolia is more diverse,which indicates that Alhagi Sparsifolia may adopt the drought adaptation strategy of"Multi angle".The results of this study have a positive effect on the in-depth understanding of the growth status and adaptability of Haloxylon ammodendron and Alhagi Sparsifolia in arid desert,and the theoretical explanation of the changes of carbon and water processes of Haloxylon ammodendron and Alhagi Sparsifolia in the face of drought stress.The results are helpful to the conservation and diversity maintenance of desert plants.