Response Of Stomata And Cuticular Wax On Leaves In Xerophyte Zygophyllum Xanthoxylum To Abiotic Stresses

Drought,soil salinization,and extreme high temperatures have an enormous impact on plant growth,agricultural productivity,and food security.Zygophyllum xanthoxylum is a widely distributed in the desert regions of Northwestern China and Central Asia.It has a strong adaptability to extreme environments such as extreme drought and high temperature,and has evolved a special adaptation mechanism in morphological structure,including thick developed cuticle,thick wax cover,developed water storage structure,and the larger but fewer stomata.Stomata and cuticular wax,as the first interface between plants and environment,play an important role in maintaining water balance and resisting abiotic stresses.Previous studies found that large amounts of alkanes(especially C₃₁ alkanes)accumulated on leaves in Z.xanthoxylum under salt or drought treatment.As another way of water loss,how does stomata play a role in response to salt or drought stress in Z.xanthoxylum?In addition,high temperature is one of the unavoidable environmental factors in the habitat of Z.xanthoxylum.How do the cuticular wax and stomata respond to high temperature and drought stresses?In view of this,this experiment starts from stomatal and non-stomatal water loss,in order to reveal the physiological mechanism of stress resistance by determining the relevant photosynthetic parameters,stomatal indexes,wax content and components,and draw the following conclusions:1.Under salt treatment(50 mmol/L NaCl),the diurnal variation of leaf net photosynthetic rate increased firstly and then basically maintained a stable trend,which was significantly higher than the control group with the extension of time in the afternoon,while the stomatal conductance and transpiration rate were significantly lower than the control group.The diurnal changes of leaf net photosynthetic rate,stomatal conductance and transpiration rate showed a gradually increasing trend under drought treatment(30%FWC),and the indexes mentioned above were significantly lower than the control under drought treatment.2.The variation of carbon stable isotope composition(?¹³C)in the leaves of Z.xanthoxylum was from-36.43‰to-36.17‰,indicating that Z.xanthoxylum was a typical C₃ plant.Compared with the control,the value of?¹³C increased significantly under salt and drought treatment,it also shows that Z.xanthoxylum can adapt to adversity by improving long-term water use efficiency.3.Under salt,drought,drought and high temperature treatment(30%FWC+6 h/d40°C),the length,width,girth,area and aperture of stomata in the epidermis on leaves were lower than those in the control group,while the stomatal density and stomatal index were higher than the control group.Compared with the control,the stomatal length,width,girth,area,aperture,density,potential stomatal conductance index and stomatal index in the epidermis on leaves of the Z.xanthoxylum increased significantly under high temperature treatment.4.In Z.xanthoxylum,the water loss and chlorophyll leaching of excised leaves exhibited relative high rate under high temperature treatment(6 h/d 40°C).In addition,high temperature treatment led to a 44%decrease in total cuticular wax content on leaves.The content of alkanes,primary alcohols and aldehydes reduced by 32%,96%and 65%,respectively.C₃₁ alkane,the overwhelming dominant component in the alkanes,decreased by 32%on leaves under high temperature treatment,but there was no significant difference in relative abundance of C₃₁ alkane.5.In Z.xanthoxylum,the relative water content of leaves decreased significantly,and the water loss and chlorophyll leaching of leaves displayed relative low rate under drought and high temperature treatment.In addition,compared with the control,the total cuticular wax load on leaves increased by 33%under drought and high temperature treatment.The content of alkanes,primary alcohols and aldehydes increased by 62%,27%and 49%,respectively.There was no obvious change in content of triterpenes.In alkanes,the content of C₃₁1 alkanes increased by 44%compared with the control,there was no significant difference in relative abundance of C₃₁ alkane.