Study On Physiological Mechanism Of Phosphorus On Camellia Oleifera Seedling Under Aluminum Stress

Camellia oleifera is an important edible oil tree species in China.The development of C.oleifera industry has many benefits,such as alleviating the shortage of edible oil,consolidating the achievements of poverty alleviation,promoting rural revitalization and ecological construction.The planting area of C.oleifera is up to 4 million hectares which mainly distributed in the acid red soil area south of the Yangtze River in China.High aluminum(Al)concentration and low available phosphorus(P)content in acidic soils of southern China are two important limiting factors limited plant growth,which not only restrict the yield of C.oleifera,but also inhibit the growth and development of seedlings.In order to investigate the effect of P deficiency and Al stress on growth and physiological indices of C.oleifera seedlings,a pot experiment was carried out with one-year-old C.oleifera ’Huajin’ cuttings.The growth and antioxidant physiology,cell wall Al accumulation and cell wall characteristics,and root physiological indics and metabolism physiology were determined by setting up four treatments:+P-Al,-P-Al,+P+Al,and-P+Al.The aim of this paper is to provide reference for the mechanism of P application to alleviate Al stress and nutrient management of C.oleifera.The main results are as follows.(1)Effects of growth and antioxidant physiology of C.oleifera showed that-P+Al treatment significantly inhibited the biomass of C.oleifera plants,and the plant dry weight decreased by 39.81%,while the addition of P alleviated the inhibition of plant growth by Al stress,and the dry weight of C.oleifera plants increased by 36.94%.The-P+Al treatment significantly reduced chlorophyll content and inhibited photosynthesis,while P addition increased chlorophyll content,reduced light inhibition,increased light capture and electron transfer efficiency,and improved net photosynthetic efficiency.The-P+Al treatment increased the PPO activity of roots and leaves,decreased antioxidant enzyme activity,and led to the accumulation of reactive oxygen species,while P addition decreased the PPO activity,alleviated the inhibition of POD and APX activity by Al stress,and reduced the accumulation of reactive oxygen species.In addition,P addition reduced the increase of cell wall bound phenol content and reduced the rate of cell wall lignification.(2)The results of the study on the cell wall related indics of C.oleifera roots showed that showed that Al stress inhibited the root elongation of C.oleifera.About 80%of Al in the root tip is distributed on the cell wall under Al stress,while 80%of Al in the cell wall binds to pectin and HC1 components.The addition of P reduces Al accumulation in the cell wall.A1 stress significantly increases pectin content in the cell wall,induces a 4-fold increase in demethyl esterification and reduces the degree of methyl esterification of pectin,while the supply of P reduces the content of demethylated pectin and HC1 in the cell wall to reduce the binding site of Al in cell wall.Moreover,the addition of P alleviated the inhibition of xyloglucan endotransglucosylase and endo-β-1,4-glucanases activities under Al stress,which enhanced the loosening of the cell wall.Moreover,P addition under Al stress increases the loosening of cell wall by reducing the inhibition of XET and EGase activity and reduced the rate of lignification by reducing CPO activity,which improved the elongation ability of cell wall to alleviate the inhibition of root elongation by Al stress.(3)The results of the study on the root metabolomics of C.oleifera showed that showed that P deficiency and Al stress decreased soluble sugar and soluble protein content,increased the content of free amino acid and MDA,while the supply of P increased soluble sugar and soluble protein content under Al stress,and decreased free amino acid and MDA content.The profiles of 58 metabolites were significantly changed in roots of oil tea seedlings.Al toxicity increased various amino acids,but decreased many kinds of organic acids and carbohydrates.Interestingly,P addition reduced the amino acids accumulation which were induced by Al toxicity,while only a few organic acids changed under P supply.Most carbohydrates,including sucrose and glucose,significantly increased with P addition under Al toxicity.Results indicated that Al toxicity increased the accumulation of amino acids and reduced the accumulation of organic acids and carbohydrates,while the addition of P promoted root growth by alleviating the inhibition of protein synthesis and increasing carbohydrates content.To sum up,P deficiency and Al stress inhibited the growth and root elongation of C.oleifera seedlings,caused oxidative stress,increased Al accumulation in root tips and affected the metabolic process,while P supply alleviated Al stress by increasing antioxidant enzyme activity to reduce oxidative stress,changing cell wall characteristics to reduces Al binding sites,and accumulating carbohydrate.