Study On The Characteristics Of Root Secretion And The Physiological Mechanism Of Organic Acid Alleviation On Pinus Massoniana Seedlings Under Aluminum Toxicity

Pinus massoniana is the Main Forestation pioneer species in the south of China.It has important use value in desert afforestation,gully control,garden greening and so on.It is also one of the main timber tree species in China,which is mainly used in providing furniture,building,wood fiber industry and other materials.But in recent years,the phenomenon of large area growth decline and even death of Pinus massoniana forest has been found.It is believed that the active aluminum in the acid soil is the main cause of the growth of Pinus massoniana and the large area of Masson Pine death.Active aluminum can not only inhibit the exchange and absorption of soil water and cation(Ca²⁺,Mg²⁺,K⁺,Cu²⁺,etc.),but also affect plant growth by destroying plant root cells and so on.The roots of the plants is the first by the toxicity of aluminum parts,showing spindle elongation was inhibited,root rough,brown,apical and lateral thick and brittle,shoot off,root epidermis and exodermis cell damage,root necrosis.Therefore,how to alleviate the toxicity of aluminum in masson pine and improve the aluminum tolerance of Masson pine is a scientific problem to be solved urgently.The root exudates of plant growth and development in the external environment to release all kinds of organic chemicals in general,including low molecular weight organic acids,amino acids,phenols,saccharides and high molecular weight,nutrient ions,enzymes such as viscose.Root exudates play an important role in plant stress recovery.Environmental stress will stimulate plants to regulate their own roots to secrete large amounts of organic matter and inorganic substances to alleviate the damage caused by adversity.Therefore,the study of the changes in the root exudates of the adversity plants has an important role in improving plant resistance and alleviating plant toxicity.Therefore,this study used the hydroponics experiment in the experimental group of different provenances of Pinus massoniana?29 genotypes?of Al tolerance based on the results of selected aluminum resistant FJ5 and aluminum sensitive GD20 Masson test materials,study characteristics of Pinus massoniana root exudates and the effect of aluminum acid on apical relief mechanism.The research mainly consists of two parts,one is to study under aluminum stress in root exudation characteristics,root exudates collected for Pinus massoniana Seedlings in different concentration of aluminum and the main components and their contents were determined to reveal under aluminum stress in masson pine root secretion differences and different characteristics of aluminum resistant root genotype the secretion characteristics of Pinus massoniana;Two is the mechanism of organic acids on root tips to alleviate Al toxicity,were determined by applying exogenous organic acids on root growth,root tip acid aluminum under the environment of H2O2,MDA,peroxidase activity,root cell wall polysaccharides and root organic acid synthase,to reveal the root exudates on soil acid aluminum environment the mechanism of alleviating aluminum toxicity.The main results are as follows:1?Low concentration aluminum treatment promoted the root growth of FJ5,while the root growth of GD20 continued to be inhibited under aluminum.The secretory characteristics of two genotypes of Masson pine at the concentration of 10 D and 20 d were compared.It was found that the secretion of organic acid,protein and amino acid in the root of aluminum tolerant Masson Pine under the action of aluminum concentration was higher than that of aluminum sensitive masson pine.At 20 d al treatment,the organic acid secretion of FJ5 increased significantly at the concentration of A3 and A5,while the content of organic acids secreted by the root increased gradually with the increase of the concentration of GD20.It shows that organic acids,proteins and amino acids play a major role in alleviating aluminum toxicity in aluminum type masson pine,and aluminum is one of the reasons that can induce more organic acids to be secreted in aluminum tolerant masson pine.The acid phosphatase activity of the root exudates of FJ5 was higher than that of GD20,and the enzyme activity of two species of Masson Pine increased first and then decreased with the increase of aluminum concentration.It shows that aluminum tolerant masson pine can promote the formation of inorganic phosphorus in soil by secreting more acid phosphatase,and reacts with excess aluminum ions in the soil to produce precipitation and environmental soil aluminum toxicity.2?Aluminum toxicity increases the content of H2O2 and MDA in Pinus massoniana root tips.After the addition of exogenous organic acids,the content of H₂O₂ and MDA in the root tips of 2 Pinus massoniana could be significantly reduced,and the alleviating effect of citric acid treatment was better than that of oxalic acid treatment.The activity of peroxidase?APX,POD,GR?of Pinus massoniana root apex was increased under the action of single aluminum,The increase in the activity of FJ5in POD and GR is higher than that of GD20,After citric acid and oxalic acid addition,the changes of APX and POD activities were relieved.Citric acid treatment had a better effect on FJ5,while oxalic acid treatment had better effect on GD20.The activity of GD20 root tip GR decreased after adding organic acids,and the alleviating effect of the two acids had little difference.Citric acid treatment increased the activity of FJ5 GR enzyme,and oxalic acid treatment reduced the activity of FJ5 root tip enzyme.3?Under the action of aluminum,the activity of glycolate oxidase and NAD-IDH in the root apex of FJ5 increased significantly.The activity of PEPCase and CS in the root apex of GD20 increased,while the activity of NAD-IDH became smaller.Citric acid treatment had an effect on the activity of glycolate oxidase,CS and NAD-IDH at the root tip of FJ5,and significantly reduced the PEPCase activity of GD20.Oxalic acid treatment had effects on the activity of glycolate oxidase,PEPCase,CS and NAD-IDH at the root tip of FJ5,and was related to the PEPCase activity of GD20 root apex.It can be seen that the PEPCase activity of Pinus massoniana is closely related to the aluminum tolerance of organic acids.Aluminum treatment reduced the activity of FJ5 apical acid phosphatase,increased the activity of GD2O,increased the activity of FJ5 after adding organic acids,and citric acid treatment significantly decreased the activity of GD20 acid phosphatase.4?Under aluminum stress,the content of total sugar and aluronic acid in the root segments of Pinus massoniana was generally increased,and the change of polysaccharide in HC1 was more obvious,indicating that HC1 should be the main binding site of the root tip of Masson Pine in HC1.Aluminum sensitive GD20increased the cell wall polysaccharides in aluminum treatment,resulting in a greater degree of inhibition of root cells.After the addition of exogenous organic acids,the content of total sugar and aluronic acid in the pectin,HC1 and HC2 of GD20 root segments were alleviated in varying degrees.The alleviating effect of oxalic acid treatment was better than that of citric acid.After the addition of organic acids,the contents of HC1,HC2 uronic acid and the total HC1 content of the root segments of the 0¹0mm segment of the root tip cell wall were alleviated after the addition of FJ5.In general,the effect of organic acids on GD20 is more effective.