Comparative Study On Leaf Nutrient Reuse Of Wild Soybean And Soybean Seedlings Under Low Phosphorus Conditions

Phosphorus plays an important role in plant growth and reproduction.Phosphorus deficiency in crops can lead to a decrease in their yield.The application of a large amount of phosphorus fertilizer in agricultural production will cause the shortage of phosphorus resources and environmental pollution.Therefore,in order to reduce the dependence of crops on phosphorus,it is urgent to cultivate new varieties of low phosphorus tolerant crops.Wild soybean is a relative wild species of soybean,which has the characteristics of barren resistance.Its tolerance to phosphorus limited environment is higher than that of soybean.It is an excellent wild resource for improving stress tolerance in soybean.In this study,wild soybean and soybean were used as experimental materials.Under low phosphorus conditions,compared with the control,the changes and differences of ion content and the kinds,number,and metabolic pathways of small molecule metabolites in the top and basal leaves of wild soybean and soybean were analyzed,in order to compare the differences between the responses of wild soybeans and soybeans to low phosphorus conditions at the levels of inorganic mineral nutrition and organic nutrition.The tolerance mechanism of wild soybean to low phosphorus and the damage of soybean under low phosphorus conditions were revealed from the perspective of nutrient reuse.The results showed that,in inorganic mineral nutrition,compared with the control,under low phosphorus condition,Mg²⁺and Fe³⁺significantly accumulated in top and basal leaves of wild soybean,but the opposite was true in the top and base leaves of soybean.The content of SO₄^2-in the top and basal leaves of wild soybean and soybean increased significantly,and the increase was greater in wild soybean.The content of K⁺was relatively stable in the top and basal leaves of wild soybean,but the content of K⁺decreased significantly in top and basal leaves of soybean.NO₃^-increased in top leaves and decreased in basal leaves of wild soybean.H₂PO₄^-was relatively stable in top leaves of wild soybean,but decreased in basal leaves of wild soybean.H₂PO₄^-decreased significantly in top and basal leaves of soybean.This showed that wild soybean can maintain good mineral nutrient absorption to make up for the nutrient deficit under low phosphorus conditions.Under low phosphorus conditions,compared with the control,the experimental results of small molecular organic nutrients showed that the content of intermediate metabolites of TCA cycle in top and basal leaves of wild soybean increased significantly,and the metabolism of TCA cycle was enhanced,but the metabolism of TCA cycle in top and basal leaves of soybean was inhibited.In top and basal leaves of wild soybean,the contents of aspartic acid family amino acids such as paragine,threonine and lysine,glutamate family amino acids including glutamine,serine family amino acids including glycine,and aromatic amino acids including tyrosine,tryptophan and phenylalanine increased significantly,but these showed a downward trend in top leaves of soybean.The content of amino acids in basal leaves of soybean increased,and the increaing range was lower than that of basal leaves of wild soybean.Compared with the control,disaccharide metabolites such as maltose and sucrose accumulated in top leaves of wild soybean and soybean,and the increase was higher in wild soybean.The contents of hexose phosphate metabolites,including fructose-6-phosphate,glucose-6-phosphate,6-phosphogluconic acid and 2,6-diphosphate fructose in top and basal leaves of wild soybean decreased significantly compared with the control,and the decrease range of these substances in the top leaves was smaller than that in the basal leaves.The hexose phosphate metabolites in top and basal leaves of soybean also decreased,but these dropped more in top leaves.The experimental results showed that:（1）In terms of inorganic mineral nutrition,wild soybean maintained the normal growth of top leaves through the accumulation of inorganic mineral nutrients such as Mg²⁺,Fe³⁺and SO₄^2-and the relative stability of K⁺in top and basal leaves and through the relative stability of H₂PO₄^-in top leaves.However,the contents of inorganic mineral nutrients such as Mg²⁺,Fe³⁺and K⁺in the top and basal leaves of soybean were inhibited,and the reuse of H₂PO₄^-was inhibited,which caused an imbalance of inorganic mineral nutrition and damage.（2）In terms of organic nutrition,wild soybean resisted low phosphorus conditions by enhancing the TCA cycle metabolism of top and basal leaves and providing more energy for metabolic activities,while the TCA cycle metabolism in top and basal leaves of soybean was inhibited and its energy supply process was damaged.（3）Wild soybean could promote the reuse of amino acids by enhancing the metabolism of aspartate family amino acids,glutamate family amino acids,serine family amino acids and aromatic amino acids in basal leaves under low phosphorus conditions.The amino acid metabolism in top leaves of soybean was significantly inhibited,and the ability of amino acid reuse was impaired.The growth of young organs in soybean was inhibited.（4）By enhancing the disaccharide metabolism in the top leaves,wild soybean can promote the reuse of sucrose,save Pi and carry out osmotic protection to maintain the growth of the top leaves.Wild soybean can promote the reuse of Pi by inhibiting the metabolism of hexose phosphate in the basal leaves,so as to resist low phosphorus conditions.This study has laid a new research idea and theoretical foundation for the study of low phosphorus tolerance of wild soybean and the cultivation of low phosphorus tolerant soybean new varieties.It is of great significance to promote the formation of environment-friendly and sustainable agriculture in China.