Study On The Relationship Between Xylem Embolism Vulnerability And Drought Resistance In Rhododendron

Drought stress leads to xylem embolism,affecting the normal water transport function of plants,which is one of the important factors limiting plant survival,growth and development.In recent years,global warming(especially with increase of frequency of extreme drought events)has led to massive tree mortality and severe forest degradation,which has seriously reduced the structure and function of forest ecosystems.Therefore,the study of xylem embolism has become a research topic and important in the context of global change.This study used three shrubs Rhododendron and 10 species of alpine Rhododendron as materials.Optical visualization technology was used to identify and quantify embolism in the petals and leaves of three shrubs Rhododendron,and a Weibull function(V=(x-100)log(1-x/100))was used to fit the water potential and embolism percentage to obtain the embolism vulnerability curve,determine petal and leaf anatomical structural traits,and analyze the correlation between xylem hydraulic function and anatomical structural traits;Similarly,10 species of alpine Rhododendron were used to construct embolism vulnerability curves using optical techniques and Weibull function(V=(x-100)log(1-x/100))and assess embolism resistance among these species.The correlations between embolism resistance and xylem conduit structure,leaf morphology and physiological traits were analyzed to explore the internal factors affecting drought tolerance.This study was conducted to provide a scientific basis for the selection and cultivation of drought-tolerant Rhododendron and a theoretical guide for the selection of tree species in arid regions.The main research results are as follows:1.The P12,P50 and P88 values(water potential values corresponding to the occurrence of 12%,50%and 88%embolism)of petals in Rhododendron ’zihe’,Rhododendron ’yangmeihong’ and Rhododendron simsii were higher than leaves,indicating that under drought stress,the three shrub Rhododendron preferentially sacrificed their petals to protect the plant leaves.The embolism vulnerability of petal and leaf tissues showed some variation among the three species,the speed of petal and leaf embolism occurring did not coincide,the embolism vulnerability of petals is:’yangmeihong’>Rhododendron simsii>’zihe’,and the embolism vulnerability of leaves is:’yangmeihong’>’zihe’>Rhododendron simsii.This variation may be an important feature of hybrid horticultural plants;Correlation analysis of P50 values of three shrubs Rhododendron with their morphological characteristics showed that the P50 values of leaves were negatively correlated with leaf palisade tissue thickness and the P50 values of petals were positively correlated with petal thickness,indicating that the thicker the leaf fenestration tissue the more drought resistant the plant was,and the thinner the petal thickness the more drought resistant the plant was among the three shrub Rhododendron.2.10 species of alpine Rhododendron showed embolism resistance as follows:R.liliiflorum>R.delavayi>R.siderophyllum>R.irroratum>R.Cavaleriei>R.annae>R.fortunei>R.thayerianum>R.platypodum>R.auriculatum.Regression analysis showed that vessel diameter was significant positively correlated with P5O(R2=0.44,P=0.03),conduit wall span was significant positively correlated with P50(R2=0.64,P=0.005),and the safety index of duct implosion(t/b)2 was significant negatively correlated with P50(R2=0.67,P=0.004).Leaf morphology and physiological traits were not correlated with P50(P>0.05).This indicates that vessel diameter,conduit wall span,and(t/b)2 can be used as reference indicators for screening drought-resistant Rhododendron species.The smaller the vessel diameter,the more drought-resistant Rhododendron;the smaller the conduit wall span,the more drought-resistant Rhododendron;the larger the(t/b)2,the more drought-resistant Rhododendron.3.Water control of R.auriculatum and R.liliiflorum were used to determine the drought resistance.The results showed that the drought resistance of R.auriculatum was lower than that of R.liliiflorum.The results of embolism vulnerability showed that the P50 value of R.auriculatum(-4.40 MPa)was higher than that of R.liliiflorum(-6.44 MPa),indicating that the leaf P50 value of the 10 studied species in alpine Rhododendron can be used to evaluate their drought resistance.In summary,the xylem vessel structure of different Rhododendron species shows differences,resulting in different embolism resistance and drought resistance.Under drought stress,plants damage petals to protect their leaves are a survival strategy for plants under drought stress.