Response Of Seed Germination Of Dominant Tree Species To Cd And Acid Stress In Waste Land Of Changting Rare Earth Mine

Changting County,Fujian is an ionic rare earth ore district.In recent years,the large amount of mining and smelting of rare earth ore have resulted in a large area of abandoned lands,which not only seriously damaged the soil structure and vegetation,caused soil erosion,but also caused soil acidification,heavy metal pollution and other ecological environment degradation problems.Therefore,the ecological restoration of abandoned land in Changting has become a major environmental problem that needs to be solved in the local area.Research shows that,soil acidification and heavy metal pollutio n are the main factors affecting ecological restoration of waste land of Changting rare earth mine.It was found that in the process of controlling the abandoned land of Changting rare earth mine,Liquid ambar formosana,Schima superba,Lespedeza bicolor,and Pinus massoniana had achieved ideal restoration effect in different vegetati-on restoration models of waste land of Changting rare earth mine.And it had been widely used.However,the restoration of degraded ecosystems is a long-term process.Although artificial planting can achieve rapid greening of abandoned land vegetation.However,whe-ther the vegetation restoration effect can be maintained for a long time,and whether the ecosystem can recover itself is still unknown.Plant seed germination is the key link to determine the long-term maintenance of vegetation ecological restoration effect in abandoned land.Due to the limitation of recovery time,it is not clear wheth-er these four species can be renewed naturally in the waste land of Changting rare earth mine.The seed germination,morphological an-d physiological responses of seeds of four tree species to acid and cadmium stress are still unclear.Since they can adapt to the advers-e environment of acid and Cd pollution,so their seeds may have adaptation strategies for acid and cadmium stress.In view of this,this paper selects the seeds of Liquidambar formosana,Schima superba,Lespedeza bicolor,Pinus massoniana which are four dominant tree species for vegetation restoration in waste land of Changting rare earth mine as research objects.Different gradient cadmium concentrations(ck,5,10,20 mg·L^-1),pH values?ck,5.5,4.5,3.5?and compound stress of Cd and acid were set to simulate stress tests.The morphological indexes of seed germination and seedling growth of four tree species under different stress treatments,as well as the antioxidant system and osmotic adjustment substance content,amylase activity and hormones in different germination stages were determined.FTIR was used to analyze the functional structure of polar and polar bonds in the compounds of four tree species under different stress conditions.The morphological and physiological responses of seed germination of four tree species under different acid and cadmium stress were compared.Analysed of the correlation between seed germination characteristics and seedling growth and physiological characteristics.Comprehensive evaluation of the response of seed germination and seedling growth to acid and cadmium stress in four tree species by used membership function analysis.Finally,the morphological and physiological response strategies of seed germination and seedling growth of Liquidambar formosana,Schima superba,Lespedeza chinensis and Pinus massoniana under Cd and acid stress were revealed.In order to provide a scientific basis for the restoration of vegetation in mining wasteland in China.The main findings are as follows:?1?With the decrease of pH value,the seed germination rate,germination potential and germination index of Liquidambar formosana,Schima superba and Pinus massoniana all increased at first and then decreased.The pH-5.5 could promote the seed germination of Liquidambar formosana,Schima superba and Pinus massoniana.However,the pH-3.5 had inhibitory effect.Acid stress had little effect on seed germination of Lespedeza chinensis.Cd stress inhibited seed germination of Lespedeza chinensis.The vigor index of Liquidambar formosana seeds decreased significantly with the increase of Cd stress concentration.Cd stress promoted the germination of Pinus massoniana seeds.Cd-10 treatment promoted the seed germination of Schima superba,but other treatments had inhibitory effects.?2?The pH-5.5 and pH-4.5 promoted the growth of Liquidambar formosana,Schima superba,and Pinus massoniana,but the pH-3.5inhibited the growth of the shoots of the three tree species,and the roots were more sensitive to acid stress.Cd stress significantly inhibited the growth of Lespedeza chinensis seedlings,but had no significant effect on Schima superba.Cd stress showed the trend of“promotion at lower concentration,but inhibition at higher concentration”on the growth of Liquidambar formosana and Pinus massoniana seedlings.The Cd-5 had a certain promoting effect on the growth of Liquidambar formosana and Pinus massoniana seedlings.When the Cd concentration was greater than10 mg·L^-1,it had an inhibitory effect on the Liquidambar formosana and Pinus massoniana.In particular,it had significant inhibition on root system.?3?Under acid stress,there were some differences in antioxidant enzyme activities,soluble protein and reducing sugar content in four tree species at different germination stages.Treatment with pH-4.5 and pH-5.5 in the dew-white stage of seeds increased the CAT activity of Pinus massoniana,the POD activity of Liquidambar formosana,Lespedeza chinensis and Pinus massoniana,and the SOD activity of Schima superba,Lespedeza chinensis and Schima superba.Acid stress could promote the soluble protein of Liquidambar formosana and Schima superba,and the sugar of Schima superba,Lespedeza chinensis and Pinus massoniana.With the decrease of pH value,the soluble sugar content of Liquidambar formosana,Schima superba and Pinus massoniana increased at first and then decreased.The CAT activity of Liquidambar formosana and the SOD activity of Schima superba increased first and then decreased during germination period.However,the CAT activity of Lespedeza chinensis and Schima superba and the activity of SOD of Lespedeza chinensis and Pinus massoniana were first reduced and then increased.Acid stress promoted CAT activity of Pinus massoniana,reducing sugar content of Liquidambar formosana and Pinus massoniana,and soluble sugar of Lespedeza chinensis.?4?Under Cd stress,there were some differences in antioxidant enzyme activities,soluble protein and reducing sugar content in four tree species at different germination stages.As the Cd concentration increases,in the dew-white stage of seeds the SOD activity of Schima superba,Lespedeza chinensis and Pinus massoniana and activities of CAT and POD in Lespedeza chinensis and the soluble sugar content of Schima superba and Pinus massoniana increased first and then decreased.Cd-20significantly increased the POD activity of Pinus massoniana,Lespedeza chinensis and Schima superba and the proline content of Lespedeza chinensis and Pinus massoniana and the soluble sugar content of Lespedeza chinensis.Cd stress significantly promoted the soluble protein of Liquidambar formosana and the reducing sugar content of Schima superba,Lespedeza chinensis and Pinus massoniana.In the germination stage,the CAT activity of Pinus massoniana,the reducing sugar content and soluble sugar content of Schima superba and Pinus massoniana increased first and then decreased.The soluble protein content of Liquidambar formosana and Pinus massoniana decreased first and then increased.POD activity in Pinus massoniana and Liquidambar formosana increased gradually.Cd stress promoted the SOD activity of four tree species.Increasing SOD activity may be the main response strategy of seed germination of four tree species to cadmium stress.?5?With the decrease of pH value,the activity of?-amylase and?-amylase of Liquidambar formosana increased first and then decreased.And increasing gibberellin content in Liquidambar formosana.The gibberellin content of Schima superba and Pinus massoniana decreased first and then increased,while Lespedeza chinensis that of arborvitae was opposite.The pH-5.5 treatment significantly promoted the?-amylase activity of Liquidambar formosana and Pinus massoniana in the dew-white stage of seeds.The pH-5.5 treatment at the germination stage significantly increased the?-amylase activity of Schima superba and Pinus massoniana.With the increase of Cd concentration,in the dew-white stage of seeds the activity of?-amylase in Schima superba decreased at first and then increased,while it was opposite at the germination stage.The?-amylase activity of Liquidambarbus formosana,Lespedeza chinensis and Pinus massoniana all increased first and then decreased in the dew-white stage of seeds.The activity of?-amylase of Lespedeza chinensis and Pinus massoniana increased first and then decreased at germination stage.Gibberellin content of Liquidambar formosana,Schima superba and Pinus massoniana increased first then decreased.?6?Fourierinfraredspectroscopyanalysisshowedthat,Liquidambar formosana could speed up the decomposition of carbohydrates under the treatment of pH-4.5 and Cd-10.Schima superba and Lespedeza chinensis could decompose carbohydrates more quickly under Cd-5 treatment.Promoted the synthesis and secretion of synthetic proteins,amino acids,peptides,and organic acids.At the same time,Schima superba and Lespedeza chinensis could secrete ester compounds and phenyl hydroxy,alcohol,ester,ether or phenol in lignin.And it could conducive to the germination of seeds.Cadmium complex stress promoted the synthesis and secretion of amino acids,peptides and proteinaceous substances from Schima superba,Lespedeza chinensis and Pinus massoniana and used to achieve Cd detoxification.And it also promoted the seed germination of Schima superba,Lespedeza chinensis and Pinus massoniana,but inhibited the seed germination of Liquidambar formosana.Pinus massoniana had strong tolerance to acid stress.The content of total sugar,cellulose,hemicellulose,protein and vitamins in the seeds of Pinus massoniana treated with pH-3.5 reached the maximum.In addition,the cell wall had a fixed effect on Cd²⁺and a sulfhydryl group?S-H?was involved in the formation of metallothionein.?7?The subordinate function analysis of morphological and physiological indexes of seed germination of four tree species showed that,the total membership functions of Liquidambar formosana and Pinus massoniana under pH-4.5,Cd-5 treatment and Schima superba at pH-5.5+Cd-5,pH-5.5,Cd-10 and Cd-5 were higher than CK.It could be seen that the above treatment could promote the seed germination and seedling growth of Liquidambar formosana,Pinus massoniana and Schima superba.However,both the pH-3.5 and Cd-20 had different inhibitory effects on Liquidambar formosana,Pinus massoniana and Schima superba.However,the membership function value of Lespedeza chinensis was lower than that of CK,and the overall performance was inhibition.In summary,the seeds of Liquidambar formosana,Schima superba,Lespedeza chinensis and Pinus massoniana had different stage response to Cd and acid stress.A certain concentration of acid and Cd stress was beneficial to seed germination and seedling growth of four tree species.In addition,the cell wall had a fixation effect on Cd²⁺and mercapto?S-H?was involved in the formation of metallothionein to limit cadmium ion toxicity.Antioxidant enzymes and osmotic adjustment substances could be induced in different germination periods to remove excess reactive oxygen species in the body and improved the antioxidant capacity of the plants.At the same time,amylase activity and gibberellin played a key role in seed germination of four tree species,and it promoted the germination of seeds of four tree species under acid and cadmium stress.It achieved detoxification and acid resistance to cadmium,thus adapting to cadmium and acid stress.