Study On Variations In Leaf Traits And Adaptive Strategies Of Ligustrum Lucidum Ait.under Lead Stress

Heavy metal lead is one of the main pollutants in the environment at present.Phytoremediation is a green environment-friendly remediation technology for heavy metal pollution.Screening of native trees that are resistant to heavy metals is a hot issue in the research of soil heavy metal phytoremediation technology.Leaf traits are not only the physiological and morphological characteristics of the plant itself,but also the adaptability of the plant to environmental conditions.Therefore,studying the response differences of plant leaf traits under lead stress will help to deepen the understanding of the ecological adaptability of tolerant plants under heavy metal stress,with a view to providing data for screening and repairing tree species.This paper takes the one-year-old tree of Ligustrum lucidum Ait.,a common garden tree species in Hunan,as the research object,and uses indoor pot experiments to set up three different concentrations of PbCl2 solution(calculated based on the amount of Pb2+ in the soil,and the concentrations are CK:0 mg·kg-1 respectively);L1:300 mg·kg-1;L2:600 mg·kg-1;L3:1800 mg·kg-1).After 15 days of application,the gas exchange parameters were measured.At the same time,the leaves were collected to determine the leaf structural characteristics and leaf physiology.Indicators and leaf Pb content.Analysis of leaf trait variation and ecological adaptation strategies of Ligustrum lucidum Ait.under lead stress.The main research results are as follows:1.Lead stress caused the net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)of Ligustrum lucidum leaves to be significantly lower than that of the control,and all showed CK>L1>L2>L3 and intercellular CO2 concentration(Ci)increased significantly.It indicated that lead stress significantly inhibited the photosynthetic rate of Ligustrum lucidum Ait.leaves,and the decrease in photosynthetic rate was mainly caused by non-stomata limiting factors.Using the modified rectangular hyperbolic model to simulate the CO2 response curve of Ligustrum lucidum Ait.leaves under lead stress,we found that under lead treatment,the maximum net photosynthetic rate(Pnmax),initial carboxylation efficiency(CE0)and photorespiration rate of Ligustrum lucidum Ait.leaves(Rp)were significantly lower than the control.The L1 treatment level CO2 saturation point(Cisat)decreased by 16.7%compared to CK,the L2 treatment level was basically unchanged compared to CK,and the L3 treatment level increased by 12%compared to CK The CO2 compensation point(Cic)of Ligustrum lucidum Ait.leaves decreased by 7.9%compared with CK at the L1 treatment level,and the L2 and L3 treatment levels increased by 21.6%and 49.8%compared to CK,respectively,indicating that the lead treatment showed that The CO2 response process of Ligustrum lucidum Ait.leaves was significantly affected,and the higher the lead treatment concentration,the larger the parameter change range of the CO2 response process.2.Under lead stress,the stomatal density(SD)of Ligustrum lucidum Ait.leaves increased by 30.2%,73.3%,and 123.8%compared with CK,and the specific leaf mass(LMA)increased by 40.3 compared with CK,respectively.%,70.2%and 134.5%,the blade thickness(LT)increased by 8.8%,24.4%and 25.8%compared to CK,SD,LMA and LT all showed CK<L1<L2<L3.It showed that the leaves of Ligustrum lucidum Ait.increased the number of stomata per unit area and the thickness of mesophyll to increase the input of leaf resources.3.Compared with CK,SOD activity of Ligustrum lucidum Ait.leaves increased by 4.8%,21.2%,and 10.7%at L1,L2,and L3 treatment levels.POD and CAT activities at L1,L2,and L3 treatment levels were significantly higher than CK,and were expressed as CK<L1<L2<L3,indicating that the antioxidant enzyme system of Ligustrum lucidum Ait.leaves was activated under lead treatment.Compared with CK,the soluble sugar content(SS)of Ligustrum lucidum Ait.leaves increased by 32.2%,56%,and 96.5%,the leaf starch content(LS),leaf nitrogen content(LN),and chlorophyll content(LC)was significantly lower than CK,and showed CK>L1>L2>L3.Compared with CK,the lead concentration of Ligustrum lucidum Ait.leaves increased by 56.8%,110%and 204%at the treatment levels of L1,L2 and L3,respectively.It showed that the accumulation of organic matter and osmotic pressure of Ligustrum lucidum Ait.leaves were significantly affected by lead treatment,starch synthesis was hindered,the content of soluble sugar in small molecules increased significantly,the nitrogen content of leaves decreased significantly,the chlorophyll synthesis process of the leaves was disturbed,and the lead inside the leaves content increased significantly.4.The Pb content of Ligustrum lucidum Ait.leaves under lead stress was significantly correlated with most of the leaf parameters.The leaf photosynthetic parameters,structural traits and physiological traits of Ligustrum lucidum Ait.showed a significant correlation,which was consistent with the leaf economic spectrum theory.Under different lead treatments,Ligustrum lucidum Ait.has formed a set of trade-off strategies that affect the functional traits of the leaves.From low concentration to high concentration lead treatment,the leaves of Ligustrum lucidum Ait.gradually changed from the "fast investment-return" type to "slow investment-return" type,which proves that Ligustrum lucidum Ait.has a certain tolerance to lead stress.To sum up,the treatment of heavy metal lead can inhibit the photosynthesis and CO2 response process of Ligustrum lucidum Ait.leaves,and affect the structure and physiological characteristics of the leaves.With the increase of the level of lead treatment,Ligustrum lucidum Ait.can increase the input of leaf resources by increasing non-structural carbohydrates(soluble sugars),leaf thickness(LT),and the number of stomatal density(SD).From the "quick investment-return" type of faster resource flow rate and return efficiency to the "slow investment-return" type of slower resource flow speed and return efficiency,increasing tolerance to lead stress.Therefore,Ligustrum lucidum Ait.can be used as a potential garden woody plant for the repair of lead contaminated soil.