The Stoichiometrc Relationship And Metabolic Regulation Strategy Of Suaeda Salsa In Different Coastal Habitats

Carbon(C),nitrogen(N)and phosphorus(P)are the main components of biological molecules,such as nucleic acid,proteins and carbohydrates,which are essential to plant growth and metabolism.Many research findings that there is a significant quantitative relationship between plant metabolic rates and ecological stoichiometry.Metabolism is an important way for plants to adapt environmental stresses,and also has a significant correlation with environmental changes.Therefore,the species of Suaeda salsa in the supratidal and intertidal habitats of coastal wetland were selected as the research objects.Based on the skills of ecological stoichiometry and metabolomics,we hope to explore the responses and adaptation strategies of Suaeda salsa under the different abiotic stresses,so as to provide theoretical basis and scientific data for understanding the ecological strategies of wetland plants under climate changes.The main results are as follows:(1)The Relative growth rate(RGR)of up-ground part of Suaeda salsa was higher than that of below-ground part in both of the two habitats.The RGR of Suaeda salsa in the supratidal habitat was higher than that in the intertidal habitat.The soil salinity of the intertidal habitat was significantly higher than that in the supratidal habitat,indicating the flooding and the salinity stress had opposite effects on the growth of Suaeda salsa.The biomass allocation strategies of Suaeda salsa in the two habitats were also significantly different.The leaf mass ratio,root mass ratio and root/shoot in the intertidal habitat were significantly higher than those in the supratidal habitat,while the stem mass ratio was contrary.Those finds were similar with the phenotypic characters of the two habitats.(2)The concentrations of N and P in leaves were higher than roots in the supratidal habitat,while in the intertidal habitat those concentrations in leaves were lower than roots,which suggested that the nutrient allocation strategies of Suaeda salsa were different under the two different habitats.The concentrations of N and P,and N/P ratios in roots,stems and leaves in the supratidal habitat were significantly higher than those in the intertidal habitat.The concentrations of N and P in the soil of the intertidal habitat were significantly higher than those in the supratidal habitat,which suggested that the differences of C/N,C/P and N/P ratios of Suaeda salsa in different habitats might come from the difference of N,P absorption strategies and their use efficiencies;The N/P ratios of leaves in the two habitats were higher than the critical threshold of 16,indicating the plant productivity in the two habitats might be limited by P.(3)UHPLC-QTOF/MS was used to analyze the metabolites of Suaeda salsa in different habitats and organs,and 61 differential metabolites were obtained.Sugar is the main product of plant photosynthesis,and the content of sugar in roots is significantly higher than that in leaves in the two habitats.This indicates that Suaeda salsa distributes sugar to roots,which is not only convenient for plant fixation,but also can absorb more nutrients from the surrounding environment for their growth.Amino acids(glutamine,D-proline,phenylalanine,etc.)of leaves in the supratidal habitats were significantly higher than those in the intertidal habitat,which was consistent with the variations of N and P in the leaves since the proportion of the two elements are high in amino acids.Glycine betaine,D-proline and choline are the main metabolites for Suaeda salsa to adapted to the salt stress in the coastal wetland.Sucrose,maltose,mannose and other soluble sugars are the main metabolites produced by Suaeda salsa to adapt to the flooding stress.(4)The principal component analysis(PCA)was used to analyze the correlations between stoichiometry and differential metabolites of different organs of Suaeda salsa in different habitats.The ratio of N/P was positively correlated with salt resistance,while C/N and C/P were positively correlated with C-rich metabolites(lipid),indicating that C/N and C/P were positively correlated with the C-fixation strategy of Suaeda salsa.The Suaeda salsa leaves in different habitats can use betaine to regulate cell osmotic pressure,then to absorb and utilize sodium-ion(Na~+),which is also an adaptive strategy for Suaeda salsa to adapt salt stress.The materials(differential metabolites,N and P)participation for Suaeda salsa in the supratidal habitat was relatively balanced in different organs,however more materials were allocated to the roots than the leaves of Suaeda salsa in the intertidal habitat.This finding can explain the coupling relationships of C-N and C-P between the different habitats or the different organs(leaves and roots).The contents of betaine,choline,4-aminobutyric acid and the value of N/P of the root in the intertidal habitat were lower than those in the supratidal habitat,indicating that the flooding may weaken the environmental stress intensity of salt in the coastal wetland.