Study On The Response Of Neyraudia Reynaudiana And Paspalum Wettsteinii To Acid Stress In Rare Earth Mine Wasteland

The ecological restoration of mining and smelting wasteland is an urgent environmental problem.Among them,rare earth has been exploited as an important strategic resource,resulting in a large number of wasteland.During the mining process of Changting Ion-type rare earth ore in Fujian Province,the soil not only destroys vegetation and soil structure after being excavated,transported,heap immersed,and washed with rainwater,but also causes environmental degradation problems such as soil erosion,soil acidification and soil heavy metal pollution.There is an urgent need to take measures to govern.Studies have shown that there are many factors limiting the restoration of vegetation in the wasteland of Changting Rare Earth Mine.Among them,soil acidification is one of the important limiting factors limiting vegetation restoration.The Neyraudia reynaudiana and Paspalum wettsteinii can grow normally under the harsh conditions of Changting rare earth ore,and have been widely used in the restoration of Changting rare earth mines.The Neyraudia reynaudiana and Paspalum wettsteinii can adapt to soil acidification environment to complete seed germination and growth and development,showing strong adaptability.There is bound to be an adaptation strategy for acid stress,which is worth exploring.In view of this,the seeds and seedlings of Neyraudia reynaudiana and Paspalum wettsteinii were used as experimental materials,and different acid stress tests?pH 5.5,pH 4.5,pH 3.5?were set up.The acid stress simulation experiments were carried out in artificial climate chamber and glass greenhouse respectively.The germination index,plasma membrane integrity and cell ultrastructure of Neyraudia reynaudiana and Paspalum wettsteinii seeds under different stress conditions were determined.The photosynthetic characteristics,chlorophyll content,electrical conductivity,root activity,antioxidant enzymes,ASA,GSH,osmotic regulators and nutrient content of plants were also measured.The morphological and physiological indexes of seed germination and seedling growth of Neyraudia reynaudiana and Paspalum wettsteinii under different acid stress were compared.The morphological and physiological characteristics of the two plants under different acid stress were analyzed.The membership function comprehensively evaluated the different morphological and physiological indexes of the two plants treated by acid stress,and finally revealed the response strategies of the Neyraudia reynaudiana and Paspalum wettsteinii to acid stress,in order to provide a scientific basis for the ecological restoration of rare earth mines and similar mines.The main conclusions are as follows:?1?The acid stress had little effect on the germination rate of Neyraudia reynaudiana seeds,and the pH 5.5 and pH 4.5 treatments promoted the growth of the buds,the bud fresh weight and the dry weight of Neyraudia reynaudiana.Different acid stress treatments could increase the germination rate of Paspalum wettsteinii seeds,pH 5.5 treatment promoted the germination index and bud length of Paspalum wettsteinii seeds.pH 3.5 treatment significantly inhibited the seed germination and seedling growth of Neyraudia reynaudiana and Paspalum wettsteinii,and severely damaged the plasmalemma of root tip cells and subcellular structure of buds.The subordinate function analysis of each index of seed germination and seedling growth showed that the seed germination of Paspalum wettsteinii had stronger adaptability to the acid stress environment and it was suitable for the application of vegetation restoration in the wasteland of Changting Rare Earth Mine.?2?The plants of Neyraudia reynaudiana and Paspalum wettsteinii have strong tolerance to acid stress,but pH 3.5 is the“threshold”of the adaptation of the two plants to the acid environment.When pH is lower than 3.5,both plants can not survive.At pH 4.5,the tiller number,leaf length,leaf width,root morphological indices and biomass of Neyraudia reynaudiana and Paspalum wettsteinii were all higher than those of pH 5.5.It shows that these two plants are more suitable for the soil pH 4.5environment,which is similar to the soil pH of the Changting rare earth ore heap leaching wasteland.?3?With the increase of stress time,the photosynthesis indexes of the leaves of Neyraudia reynaudiana and Paspalum wettsteinii showed a decreasing trend.The diurnal changes of photosynthesis of Neyraudia reynaudiana leaves showed that the diurnal changes of Pn,Gs and Tr were"double peak"curves,which were valley values at 12:00 noon,and Ci changed in the opposite direction.The diurnal variations in photosynthesis of Pn,Gs and Tr in the leaves of Paspalum wettsteinii were increased first and then decreased,which were larger at about 12:00 noon,and Ci changed in the opposite direction.Under the condition of acid stress,the fluorescence parameters of leaves of Neyraudia reynaudiana and Paspalum wettsteinii were increased,but the SPAD value and chlorophyll content were decreased.?4?Under the acid stress,with the increase of stress time,the relative conductivity,malondialdehyde and H₂O₂ content of the Neyraudia reynaudiana leaves were decreased,and the H₂O₂ content of the Paspalum wettsteinii leaves was also decreased.With the decrease of pH value,the malondialdehyde content and O₂^-production rate in the roots of Neyraudia reynaudiana and Paspalum wettsteinii and H₂O₂ content in the roots of Paspalum wettsteinii were gradually decreased,and the root activities of Neyraudia reynaudiana and Paspalum wettsteinii were increased.It indicated that the two plants could eliminate active oxygen free radicals in the body under acid stress and reduce the harm of stress.?5?With the increase of stress time,the contents of SOD,CAT,APX,ASA and soluble protein in the leaves of Neyraudia reynaudiana and Paspalum wettsteinii under the same pH treatment were increased,and the POD activity changed inversely.With the decrease of pH value,the contents of SOD,POD,ASA,proline and soluble protein in the leaves of Neyraudia reynaudiana were increased gradually at 60 d.And the activities of antioxidant enzymes,ASA and GSH in the leaves of Neyraudia reynaudiana were decreased gradually,while the content of proline and soluble sugar were increased at 90 d.The contents of CAT,ASA,GSH,proline,soluble sugar and soluble protein in the leaves of Paspalum wettsteinii were increased gradually with the decrease of pH.With the decrease of pH value,the content of APX,ASA and soluble sugar in the roots of Neyraudia reynaudiana were increased,and the contents of CAT,soluble sugar and soluble protein in the roots of Paspalum wettsteinii were also increased.?6?The absorption and transport capacity of C,N,P,K,Mg and Ca by Neyraudia reynaudiana and Paspalum wettsteinii at pH 4.5 was higher than that at pH 5.5,and the absorption and transport capacity of nutrient elements by Paspalum wettsteinii was greater than that by Neyraudia reynaudiana.?7?Through the statistical analysis of the correlations between the above-ground indicators of the Neyraudia reynaudiana and Paspalum wettsteinii,it was found that for Neyraudia reynaudiana,there were significant positive correlations among total chlorophyll content,H₂O₂,relative conductivity and MDA.And Fv/Fo and Fv were positively correlated with plant height and soluble sugar,respectively.And there was a significant negative correlation between OFR and GSH.For Paspalum wettsteinii,the tiller number and GSH were negatively correlated with total chlorophyll content and relative conductivity,respectively.Pn was negatively correlated with proline and CAT,and soluble sugar was positively correlated with Fo.The membership function analysis of various morphological and physiological indexes of N.reynaudiana and P.wettsteinii showed that both plants grew better in the soil environment of pH 4.5,and the Paspalum wettsteinii is more resistant to acid.In summary,the Neyraudia reynaudiana and Paspalum wettsteinii can adapt to the acid stress environment by accelerating the growth of leaf and root morphological indicators,promoting tillering and increasing biomass.At the same time,they can resist and repair the peroxidation damage of cells by promoting the fluorescence parameters of leaves,increasing the contents of SOD,CAT,APX,ASA,GSH and osmotic regulators and promoting the absorption and transportation of C,N,P,K,Mg and Ca.