Response Of Root Development Of Phosphorus-enriched Plant Polygonum Hydropiper To Phosphorus Supply Level And Its Relationship With Phosphorus Accumulation

Phosphorus is an essential nutrient element for plant growth and development.In agricultural production,a large amount of phosphorus fertilizer is applied due to the easy fixation,difficult movement and low availability of phosphorus in soil,which leads to soil phosphorus enrichment and thus causes environmental problems such as non-point source pollution.Excavating and applying plant resources with specific absorption or enrichment characteristics of phosphorus,and studying their absorption and accumulation mechanisms can provide methods and basis for solving the above problems.In this study,the aquatic-terrestrial plant Polygonum hydropiper was taken as the research object.Based on the previous studies,it was found that the plant had normal growth and development under low phosphorus and high enrichment characteristics under high phosphorus.Taking the root development of Polygonum hydropiper as the starting point,the hydroponic experiments under different phosphorus supply levels were carried out.Combined with the comprehensive analysis of root morphological indexes,endogenous hormone content and transcriptomics,the relationship between root development and phosphorus absorption of Polygonum hydropiper and the regulation of hormones on root development were systematically studied.The main results are as follows:（1）After low phosphorus and high phosphorus treatment,the specific root length and specific root surface area of Polygonum hydropiper root system increased significantly.The relative thickness of adventitious root cortex was 1.46-1.56 times that of normal phosphorus,and the number of lateral root primordia was 2.64-3.25 times that of normal phosphorus,which was beneficial to the development of lateral roots of Polygonum hydropiper.The distribution ratio of lateral root surface area and volume of Polygonum hydropiper increased by 1.19%-13.49%compared with normal phosphorus,which was beneficial to promote the absorption of phosphorus by Polygonum hydropiper under low phosphorus and high phosphorus conditions.The growth of Polygonum hydropiper was inhibited under low phosphorus and high phosphorus treatments,but the enrichment coefficient of the aboveground and underground parts of Polygonum hydropiper under low phosphorus treatment was 3.36-6.68 times that of normal phosphorus,and its strong phosphorus absorption capacity enabled it to maintain normal growth;Under high phosphorus treatment,the phosphorus contents in the aboveground and underground parts of Polygonum hydropiper were as high as 8.09 g kg^-1 and 12.01 g kg^-1,respectively,and the phosphorus accumulation was not significantly lower than that of normal phosphorus,indicating that Polygonum hydropiper had strong tolerance and accumulation ability to phosphorus.（2）Under different phosphorus levels,15 plant hormones related to root development and stress resistance could be detected in the roots of Polygonum hydropiper.Among them,only the contents of cytokinin,gibberellin and 1-aminocyclopropanecarboxylic acid were significantly different due to different phosphorus levels.Under low phosphorus treatment,the contents of cytokinins（IPA,TZ,TZR）decreased significantly,which were 39.56%-57.36%of normal phosphorus,and the contents of gibberellin（GA3）and 1-aminocyclopropanecarboxylic acid increased significantly,which were 1.24 times and 1.48 times of normal phosphorus,respectively;Under high phosphorus treatment,the content of cytokinin（TZ）increased significantly,which was 1.40 times that of normal phosphorus treatment.The content of cytokinin（IP,IPA）decreased significantly,which was 35.23%-46.60%times that of normal phosphorus treatment.The content of gibberellin（GA3）decreased significantly,which was 86.17%of normal phosphorus.The content of 1-aminocyclopropanecarboxylic acid increased significantly,which was 1.77 times that of normal phosphorus treatment.Correlation analysis showed that among the 15 hormones,only cytokinin was significantly positively correlated with the morphological parameters of the lateral roots of Polygonum hydropiper.At the same time,under low and high phosphorus conditions,the expression of genes encoding isopentenyl transferase and cytokinin hydroxylase in the cytokinin synthesis pathway of Polygonum hydropiper roots and genes encoding A-type and B-type response regulators in the signal transduction pathway also changed significantly,indicating that cytokinin is a key hormone to promote the development of Polygonum hydropiper roots.（3）Exogenous addition of cytokinin can increase the content of endogenous cytokinin in the roots of Polygonum hydropiper and promote the development of Polygonum hydropiper roots.Under normal phosphorus conditions,after exogenous addition of cytokinin,the endogenous cytokinin content in the roots of Polygonum hydropiper was 1.19-1.51 times that of the unadded,and the root length,surface area and volume were 1.31-2.48 times that of the unadded;Under high phosphorus conditions,after exogenous addition of cytokinin,the content of endogenous cytokinin in the roots of Polygonum hydropiper was 1.23-1.46 times higher than that without addition,and the root length,surface area and volume were 1.72-3.14 times higher than those without addition.The underground biomass and phosphorus accumulation increased significantly,and the phosphorus accumulation in the aboveground part also increased significantly,indicating that the phosphorus accumulation in the aboveground part of Polygonum hydropiper was regulated by cytokinin and phosphorus concentration.